Dictionary<TKey, TValue> Class

July 28, 2014

Represents a collection of keys and values.

System.Object
  System.Collections.Generic.Dictionary<TKey, TValue>

Namespace:  System.Collections.Generic
Assembly:  mscorlib (in mscorlib.dll)

public class Dictionary<TKey, TValue> : IDictionary<TKey, TValue>, 
	ICollection<KeyValuePair<TKey, TValue>>, IReadOnlyDictionary<TKey, TValue>, 
	IReadOnlyCollection<KeyValuePair<TKey, TValue>>, IEnumerable<KeyValuePair<TKey, TValue>>, 
	IDictionary, ICollection, IEnumerable

Type Parameters

TKey

The type of the keys in the dictionary.

TValue

The type of the values in the dictionary.

The Dictionary<TKey, TValue> type exposes the following members.

  NameDescription
Public methodDictionary<TKey, TValue>()Initializes a new instance of the Dictionary<TKey, TValue> class that is empty, has the default initial capacity, and uses the default equality comparer for the key type.
Public methodDictionary<TKey, TValue>(IDictionary<TKey, TValue>)Initializes a new instance of the Dictionary<TKey, TValue> class that contains elements copied from the specified IDictionary<TKey, TValue> and uses the default equality comparer for the key type.
Public methodDictionary<TKey, TValue>(IEqualityComparer<TKey>)Initializes a new instance of the Dictionary<TKey, TValue> class that is empty, has the default initial capacity, and uses the specified IEqualityComparer<T>.
Public methodDictionary<TKey, TValue>(Int32)Initializes a new instance of the Dictionary<TKey, TValue> class that is empty, has the specified initial capacity, and uses the default equality comparer for the key type.
Public methodDictionary<TKey, TValue>(IDictionary<TKey, TValue>, IEqualityComparer<TKey>)Initializes a new instance of the Dictionary<TKey, TValue> class that contains elements copied from the specified IDictionary<TKey, TValue> and uses the specified IEqualityComparer<T>.
Public methodDictionary<TKey, TValue>(Int32, IEqualityComparer<TKey>)Initializes a new instance of the Dictionary<TKey, TValue> class that is empty, has the specified initial capacity, and uses the specified IEqualityComparer<T>.
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  NameDescription
Public propertyComparerGets the IEqualityComparer<T> that is used to determine equality of keys for the dictionary.
Public propertyCountGets the number of key/value pairs contained in the Dictionary<TKey, TValue>.
Public propertyItemGets or sets the value associated with the specified key.
Public propertyKeysGets a collection containing the keys in the Dictionary<TKey, TValue>.
Public propertyValuesGets a collection containing the values in the Dictionary<TKey, TValue>.
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  NameDescription
Public methodAddAdds the specified key and value to the dictionary.
Public methodClearRemoves all keys and values from the Dictionary<TKey, TValue>.
Public methodContainsKeyDetermines whether the Dictionary<TKey, TValue> contains the specified key.
Public methodContainsValueDetermines whether the Dictionary<TKey, TValue> contains a specific value.
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before the Object is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetEnumeratorReturns an enumerator that iterates through the Dictionary<TKey, TValue>.
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodRemoveRemoves the value with the specified key from the Dictionary<TKey, TValue>.
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)
Public methodTryGetValueGets the value associated with the specified key.
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  NameDescription
Public Extension MethodAggregate<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, KeyValuePair<TKey, TValue>, KeyValuePair<TKey, TValue>>)Overloaded. Applies an accumulator function over a sequence. (Defined by Enumerable.)
Public Extension MethodAggregate<KeyValuePair<TKey, TValue>, TAccumulate>(TAccumulate, Func<TAccumulate, KeyValuePair<TKey, TValue>, TAccumulate>)Overloaded. Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value. (Defined by Enumerable.)
Public Extension MethodAggregate<KeyValuePair<TKey, TValue>, TAccumulate, TResult>(TAccumulate, Func<TAccumulate, KeyValuePair<TKey, TValue>, TAccumulate>, Func<TAccumulate, TResult>)Overloaded. Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value, and the specified function is used to select the result value. (Defined by Enumerable.)
Public Extension MethodAll<KeyValuePair<TKey, TValue>>Determines whether all elements of a sequence satisfy a condition. (Defined by Enumerable.)
Public Extension MethodAny<KeyValuePair<TKey, TValue>>()Overloaded. Determines whether a sequence contains any elements. (Defined by Enumerable.)
Public Extension MethodAny<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Boolean>)Overloaded. Determines whether any element of a sequence satisfies a condition. (Defined by Enumerable.)
Public Extension MethodAsEnumerable<KeyValuePair<TKey, TValue>>Returns the input typed as IEnumerable<T>. (Defined by Enumerable.)
Public Extension MethodAsQueryable()Overloaded. Converts an IEnumerable to an IQueryable. (Defined by Queryable.)
Public Extension MethodAsQueryable<KeyValuePair<TKey, TValue>>()Overloaded. Converts a generic IEnumerable<T> to a generic IQueryable<T>. (Defined by Queryable.)
Public Extension MethodAverage<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Decimal>>)Overloaded. Computes the average of a sequence of nullable Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodAverage<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Double>>)Overloaded. Computes the average of a sequence of nullable Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodAverage<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Decimal>)Overloaded. Computes the average of a sequence of Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodAverage<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Double>)Overloaded. Computes the average of a sequence of Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodAverage<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Int32>)Overloaded. Computes the average of a sequence of Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodAverage<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Int64>)Overloaded. Computes the average of a sequence of Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodAverage<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Int32>>)Overloaded. Computes the average of a sequence of nullable Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodAverage<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Int64>>)Overloaded. Computes the average of a sequence of nullable Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodAverage<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Single>>)Overloaded. Computes the average of a sequence of nullable Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodAverage<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Single>)Overloaded. Computes the average of a sequence of Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodCast<TResult>Converts the elements of an IEnumerable to the specified type. (Defined by Enumerable.)
Public Extension MethodConcat<KeyValuePair<TKey, TValue>>Concatenates two sequences. (Defined by Enumerable.)
Public Extension MethodContains<KeyValuePair<TKey, TValue>>(KeyValuePair<TKey, TValue>)Overloaded. Determines whether a sequence contains a specified element by using the default equality comparer. (Defined by Enumerable.)
Public Extension MethodContains<KeyValuePair<TKey, TValue>>(KeyValuePair<TKey, TValue>, IEqualityComparer<KeyValuePair<TKey, TValue>>)Overloaded. Determines whether a sequence contains a specified element by using a specified IEqualityComparer<T>. (Defined by Enumerable.)
Public Extension MethodCount<KeyValuePair<TKey, TValue>>()Overloaded. Returns the number of elements in a sequence. (Defined by Enumerable.)
Public Extension MethodCount<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Boolean>)Overloaded. Returns a number that represents how many elements in the specified sequence satisfy a condition. (Defined by Enumerable.)
Public Extension MethodDefaultIfEmpty<KeyValuePair<TKey, TValue>>()Overloaded. Returns the elements of the specified sequence or the type parameter's default value in a singleton collection if the sequence is empty. (Defined by Enumerable.)
Public Extension MethodDefaultIfEmpty<KeyValuePair<TKey, TValue>>(KeyValuePair<TKey, TValue>)Overloaded. Returns the elements of the specified sequence or the specified value in a singleton collection if the sequence is empty. (Defined by Enumerable.)
Public Extension MethodDistinct<KeyValuePair<TKey, TValue>>()Overloaded. Returns distinct elements from a sequence by using the default equality comparer to compare values. (Defined by Enumerable.)
Public Extension MethodDistinct<KeyValuePair<TKey, TValue>>(IEqualityComparer<KeyValuePair<TKey, TValue>>)Overloaded. Returns distinct elements from a sequence by using a specified IEqualityComparer<T> to compare values. (Defined by Enumerable.)
Public Extension MethodElementAt<KeyValuePair<TKey, TValue>>Returns the element at a specified index in a sequence. (Defined by Enumerable.)
Public Extension MethodElementAtOrDefault<KeyValuePair<TKey, TValue>>Returns the element at a specified index in a sequence or a default value if the index is out of range. (Defined by Enumerable.)
Public Extension MethodExcept<KeyValuePair<TKey, TValue>>(IEnumerable<KeyValuePair<TKey, TValue>>)Overloaded. Produces the set difference of two sequences by using the default equality comparer to compare values. (Defined by Enumerable.)
Public Extension MethodExcept<KeyValuePair<TKey, TValue>>(IEnumerable<KeyValuePair<TKey, TValue>>, IEqualityComparer<KeyValuePair<TKey, TValue>>)Overloaded. Produces the set difference of two sequences by using the specified IEqualityComparer<T> to compare values. (Defined by Enumerable.)
Public Extension MethodFirst<KeyValuePair<TKey, TValue>>()Overloaded. Returns the first element of a sequence. (Defined by Enumerable.)
Public Extension MethodFirst<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Boolean>)Overloaded. Returns the first element in a sequence that satisfies a specified condition. (Defined by Enumerable.)
Public Extension MethodFirstOrDefault<KeyValuePair<TKey, TValue>>()Overloaded. Returns the first element of a sequence, or a default value if the sequence contains no elements. (Defined by Enumerable.)
Public Extension MethodFirstOrDefault<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Boolean>)Overloaded. Returns the first element of the sequence that satisfies a condition or a default value if no such element is found. (Defined by Enumerable.)
Public Extension MethodGroupBy<KeyValuePair<TKey, TValue>, TKey>(Func<KeyValuePair<TKey, TValue>, TKey>)Overloaded. Groups the elements of a sequence according to a specified key selector function. (Defined by Enumerable.)
Public Extension MethodGroupBy<KeyValuePair<TKey, TValue>, TKey>(Func<KeyValuePair<TKey, TValue>, TKey>, IEqualityComparer<TKey>)Overloaded. Groups the elements of a sequence according to a specified key selector function and compares the keys by using a specified comparer. (Defined by Enumerable.)
Public Extension MethodGroupBy<KeyValuePair<TKey, TValue>, TKey, TElement>(Func<KeyValuePair<TKey, TValue>, TKey>, Func<KeyValuePair<TKey, TValue>, TElement>)Overloaded. Groups the elements of a sequence according to a specified key selector function and projects the elements for each group by using a specified function. (Defined by Enumerable.)
Public Extension MethodGroupBy<KeyValuePair<TKey, TValue>, TKey, TResult>(Func<KeyValuePair<TKey, TValue>, TKey>, Func<TKey, IEnumerable<KeyValuePair<TKey, TValue>>, TResult>)Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. (Defined by Enumerable.)
Public Extension MethodGroupBy<KeyValuePair<TKey, TValue>, TKey, TElement>(Func<KeyValuePair<TKey, TValue>, TKey>, Func<KeyValuePair<TKey, TValue>, TElement>, IEqualityComparer<TKey>)Overloaded. Groups the elements of a sequence according to a key selector function. The keys are compared by using a comparer and each group's elements are projected by using a specified function. (Defined by Enumerable.)
Public Extension MethodGroupBy<KeyValuePair<TKey, TValue>, TKey, TResult>(Func<KeyValuePair<TKey, TValue>, TKey>, Func<TKey, IEnumerable<KeyValuePair<TKey, TValue>>, TResult>, IEqualityComparer<TKey>)Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. The keys are compared by using a specified comparer. (Defined by Enumerable.)
Public Extension MethodGroupBy<KeyValuePair<TKey, TValue>, TKey, TElement, TResult>(Func<KeyValuePair<TKey, TValue>, TKey>, Func<KeyValuePair<TKey, TValue>, TElement>, Func<TKey, IEnumerable<TElement>, TResult>)Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. The elements of each group are projected by using a specified function. (Defined by Enumerable.)
Public Extension MethodGroupBy<KeyValuePair<TKey, TValue>, TKey, TElement, TResult>(Func<KeyValuePair<TKey, TValue>, TKey>, Func<KeyValuePair<TKey, TValue>, TElement>, Func<TKey, IEnumerable<TElement>, TResult>, IEqualityComparer<TKey>)Overloaded. Groups the elements of a sequence according to a specified key selector function and creates a result value from each group and its key. Key values are compared by using a specified comparer, and the elements of each group are projected by using a specified function. (Defined by Enumerable.)
Public Extension MethodGroupJoin<KeyValuePair<TKey, TValue>, TInner, TKey, TResult>(IEnumerable<TInner>, Func<KeyValuePair<TKey, TValue>, TKey>, Func<TInner, TKey>, Func<KeyValuePair<TKey, TValue>, IEnumerable<TInner>, TResult>)Overloaded. Correlates the elements of two sequences based on equality of keys and groups the results. The default equality comparer is used to compare keys. (Defined by Enumerable.)
Public Extension MethodGroupJoin<KeyValuePair<TKey, TValue>, TInner, TKey, TResult>(IEnumerable<TInner>, Func<KeyValuePair<TKey, TValue>, TKey>, Func<TInner, TKey>, Func<KeyValuePair<TKey, TValue>, IEnumerable<TInner>, TResult>, IEqualityComparer<TKey>)Overloaded. Correlates the elements of two sequences based on key equality and groups the results. A specified IEqualityComparer<T> is used to compare keys. (Defined by Enumerable.)
Public Extension MethodIntersect<KeyValuePair<TKey, TValue>>(IEnumerable<KeyValuePair<TKey, TValue>>)Overloaded. Produces the set intersection of two sequences by using the default equality comparer to compare values. (Defined by Enumerable.)
Public Extension MethodIntersect<KeyValuePair<TKey, TValue>>(IEnumerable<KeyValuePair<TKey, TValue>>, IEqualityComparer<KeyValuePair<TKey, TValue>>)Overloaded. Produces the set intersection of two sequences by using the specified IEqualityComparer<T> to compare values. (Defined by Enumerable.)
Public Extension MethodJoin<KeyValuePair<TKey, TValue>, TInner, TKey, TResult>(IEnumerable<TInner>, Func<KeyValuePair<TKey, TValue>, TKey>, Func<TInner, TKey>, Func<KeyValuePair<TKey, TValue>, TInner, TResult>)Overloaded. Correlates the elements of two sequences based on matching keys. The default equality comparer is used to compare keys. (Defined by Enumerable.)
Public Extension MethodJoin<KeyValuePair<TKey, TValue>, TInner, TKey, TResult>(IEnumerable<TInner>, Func<KeyValuePair<TKey, TValue>, TKey>, Func<TInner, TKey>, Func<KeyValuePair<TKey, TValue>, TInner, TResult>, IEqualityComparer<TKey>)Overloaded. Correlates the elements of two sequences based on matching keys. A specified IEqualityComparer<T> is used to compare keys. (Defined by Enumerable.)
Public Extension MethodLast<KeyValuePair<TKey, TValue>>()Overloaded. Returns the last element of a sequence. (Defined by Enumerable.)
Public Extension MethodLast<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Boolean>)Overloaded. Returns the last element of a sequence that satisfies a specified condition. (Defined by Enumerable.)
Public Extension MethodLastOrDefault<KeyValuePair<TKey, TValue>>()Overloaded. Returns the last element of a sequence, or a default value if the sequence contains no elements. (Defined by Enumerable.)
Public Extension MethodLastOrDefault<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Boolean>)Overloaded. Returns the last element of a sequence that satisfies a condition or a default value if no such element is found. (Defined by Enumerable.)
Public Extension MethodLongCount<KeyValuePair<TKey, TValue>>()Overloaded. Returns an Int64 that represents the total number of elements in a sequence. (Defined by Enumerable.)
Public Extension MethodLongCount<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Boolean>)Overloaded. Returns an Int64 that represents how many elements in a sequence satisfy a condition. (Defined by Enumerable.)
Public Extension MethodMax<KeyValuePair<TKey, TValue>>()Overloaded. Returns the maximum value in a generic sequence. (Defined by Enumerable.)
Public Extension MethodMax<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Decimal>>)Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Decimal value. (Defined by Enumerable.)
Public Extension MethodMax<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Double>>)Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Double value. (Defined by Enumerable.)
Public Extension MethodMax<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Decimal>)Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Decimal value. (Defined by Enumerable.)
Public Extension MethodMax<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Double>)Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Double value. (Defined by Enumerable.)
Public Extension MethodMax<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Int32>)Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Int32 value. (Defined by Enumerable.)
Public Extension MethodMax<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Int64>)Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Int64 value. (Defined by Enumerable.)
Public Extension MethodMax<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Int32>>)Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Int32 value. (Defined by Enumerable.)
Public Extension MethodMax<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Int64>>)Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Int64 value. (Defined by Enumerable.)
Public Extension MethodMax<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Single>>)Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Single value. (Defined by Enumerable.)
Public Extension MethodMax<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Single>)Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Single value. (Defined by Enumerable.)
Public Extension MethodMax<KeyValuePair<TKey, TValue>, TResult>(Func<KeyValuePair<TKey, TValue>, TResult>)Overloaded. Invokes a transform function on each element of a generic sequence and returns the maximum resulting value. (Defined by Enumerable.)
Public Extension MethodMin<KeyValuePair<TKey, TValue>>()Overloaded. Returns the minimum value in a generic sequence. (Defined by Enumerable.)
Public Extension MethodMin<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Decimal>>)Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Decimal value. (Defined by Enumerable.)
Public Extension MethodMin<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Double>>)Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Double value. (Defined by Enumerable.)
Public Extension MethodMin<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Decimal>)Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Decimal value. (Defined by Enumerable.)
Public Extension MethodMin<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Double>)Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Double value. (Defined by Enumerable.)
Public Extension MethodMin<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Int32>)Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Int32 value. (Defined by Enumerable.)
Public Extension MethodMin<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Int64>)Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Int64 value. (Defined by Enumerable.)
Public Extension MethodMin<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Int32>>)Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Int32 value. (Defined by Enumerable.)
Public Extension MethodMin<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Int64>>)Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Int64 value. (Defined by Enumerable.)
Public Extension MethodMin<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Single>>)Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Single value. (Defined by Enumerable.)
Public Extension MethodMin<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Single>)Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Single value. (Defined by Enumerable.)
Public Extension MethodMin<KeyValuePair<TKey, TValue>, TResult>(Func<KeyValuePair<TKey, TValue>, TResult>)Overloaded. Invokes a transform function on each element of a generic sequence and returns the minimum resulting value. (Defined by Enumerable.)
Public Extension MethodOfType<TResult>Filters the elements of an IEnumerable based on a specified type. (Defined by Enumerable.)
Public Extension MethodOrderBy<KeyValuePair<TKey, TValue>, TKey>(Func<KeyValuePair<TKey, TValue>, TKey>)Overloaded. Sorts the elements of a sequence in ascending order according to a key. (Defined by Enumerable.)
Public Extension MethodOrderBy<KeyValuePair<TKey, TValue>, TKey>(Func<KeyValuePair<TKey, TValue>, TKey>, IComparer<TKey>)Overloaded. Sorts the elements of a sequence in ascending order by using a specified comparer. (Defined by Enumerable.)
Public Extension MethodOrderByDescending<KeyValuePair<TKey, TValue>, TKey>(Func<KeyValuePair<TKey, TValue>, TKey>)Overloaded. Sorts the elements of a sequence in descending order according to a key. (Defined by Enumerable.)
Public Extension MethodOrderByDescending<KeyValuePair<TKey, TValue>, TKey>(Func<KeyValuePair<TKey, TValue>, TKey>, IComparer<TKey>)Overloaded. Sorts the elements of a sequence in descending order by using a specified comparer. (Defined by Enumerable.)
Public Extension MethodReverse<KeyValuePair<TKey, TValue>>Inverts the order of the elements in a sequence. (Defined by Enumerable.)
Public Extension MethodSelect<KeyValuePair<TKey, TValue>, TResult>(Func<KeyValuePair<TKey, TValue>, TResult>)Overloaded. Projects each element of a sequence into a new form. (Defined by Enumerable.)
Public Extension MethodSelect<KeyValuePair<TKey, TValue>, TResult>(Func<KeyValuePair<TKey, TValue>, Int32, TResult>)Overloaded. Projects each element of a sequence into a new form by incorporating the element's index. (Defined by Enumerable.)
Public Extension MethodSelectMany<KeyValuePair<TKey, TValue>, TResult>(Func<KeyValuePair<TKey, TValue>, IEnumerable<TResult>>)Overloaded. Projects each element of a sequence to an IEnumerable<T> and flattens the resulting sequences into one sequence. (Defined by Enumerable.)
Public Extension MethodSelectMany<KeyValuePair<TKey, TValue>, TResult>(Func<KeyValuePair<TKey, TValue>, Int32, IEnumerable<TResult>>)Overloaded. Projects each element of a sequence to an IEnumerable<T>, and flattens the resulting sequences into one sequence. The index of each source element is used in the projected form of that element. (Defined by Enumerable.)
Public Extension MethodSelectMany<KeyValuePair<TKey, TValue>, TCollection, TResult>(Func<KeyValuePair<TKey, TValue>, IEnumerable<TCollection>>, Func<KeyValuePair<TKey, TValue>, TCollection, TResult>)Overloaded. Projects each element of a sequence to an IEnumerable<T>, flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein. (Defined by Enumerable.)
Public Extension MethodSelectMany<KeyValuePair<TKey, TValue>, TCollection, TResult>(Func<KeyValuePair<TKey, TValue>, Int32, IEnumerable<TCollection>>, Func<KeyValuePair<TKey, TValue>, TCollection, TResult>)Overloaded. Projects each element of a sequence to an IEnumerable<T>, flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein. The index of each source element is used in the intermediate projected form of that element. (Defined by Enumerable.)
Public Extension MethodSequenceEqual<KeyValuePair<TKey, TValue>>(IEnumerable<KeyValuePair<TKey, TValue>>)Overloaded. Determines whether two sequences are equal by comparing the elements by using the default equality comparer for their type. (Defined by Enumerable.)
Public Extension MethodSequenceEqual<KeyValuePair<TKey, TValue>>(IEnumerable<KeyValuePair<TKey, TValue>>, IEqualityComparer<KeyValuePair<TKey, TValue>>)Overloaded. Determines whether two sequences are equal by comparing their elements by using a specified IEqualityComparer<T>. (Defined by Enumerable.)
Public Extension MethodSingle<KeyValuePair<TKey, TValue>>()Overloaded. Returns the only element of a sequence, and throws an exception if there is not exactly one element in the sequence. (Defined by Enumerable.)
Public Extension MethodSingle<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Boolean>)Overloaded. Returns the only element of a sequence that satisfies a specified condition, and throws an exception if more than one such element exists. (Defined by Enumerable.)
Public Extension MethodSingleOrDefault<KeyValuePair<TKey, TValue>>()Overloaded. Returns the only element of a sequence, or a default value if the sequence is empty; this method throws an exception if there is more than one element in the sequence. (Defined by Enumerable.)
Public Extension MethodSingleOrDefault<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Boolean>)Overloaded. Returns the only element of a sequence that satisfies a specified condition or a default value if no such element exists; this method throws an exception if more than one element satisfies the condition. (Defined by Enumerable.)
Public Extension MethodSkip<KeyValuePair<TKey, TValue>>Bypasses a specified number of elements in a sequence and then returns the remaining elements. (Defined by Enumerable.)
Public Extension MethodSkipWhile<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Boolean>)Overloaded. Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements. (Defined by Enumerable.)
Public Extension MethodSkipWhile<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Int32, Boolean>)Overloaded. Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements. The element's index is used in the logic of the predicate function. (Defined by Enumerable.)
Public Extension MethodSum<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Decimal>>)Overloaded. Computes the sum of the sequence of nullable Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodSum<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Double>>)Overloaded. Computes the sum of the sequence of nullable Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodSum<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Decimal>)Overloaded. Computes the sum of the sequence of Decimal values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodSum<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Double>)Overloaded. Computes the sum of the sequence of Double values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodSum<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Int32>)Overloaded. Computes the sum of the sequence of Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodSum<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Int64>)Overloaded. Computes the sum of the sequence of Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodSum<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Int32>>)Overloaded. Computes the sum of the sequence of nullable Int32 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodSum<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Int64>>)Overloaded. Computes the sum of the sequence of nullable Int64 values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodSum<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Nullable<Single>>)Overloaded. Computes the sum of the sequence of nullable Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodSum<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Single>)Overloaded. Computes the sum of the sequence of Single values that are obtained by invoking a transform function on each element of the input sequence. (Defined by Enumerable.)
Public Extension MethodTake<KeyValuePair<TKey, TValue>>Returns a specified number of contiguous elements from the start of a sequence. (Defined by Enumerable.)
Public Extension MethodTakeWhile<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Boolean>)Overloaded. Returns elements from a sequence as long as a specified condition is true. (Defined by Enumerable.)
Public Extension MethodTakeWhile<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Int32, Boolean>)Overloaded. Returns elements from a sequence as long as a specified condition is true. The element's index is used in the logic of the predicate function. (Defined by Enumerable.)
Public Extension MethodToArray<KeyValuePair<TKey, TValue>>Creates an array from a IEnumerable<T>. (Defined by Enumerable.)
Public Extension MethodToDictionary<KeyValuePair<TKey, TValue>, TKey>(Func<KeyValuePair<TKey, TValue>, TKey>)Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to a specified key selector function. (Defined by Enumerable.)
Public Extension MethodToDictionary<KeyValuePair<TKey, TValue>, TKey>(Func<KeyValuePair<TKey, TValue>, TKey>, IEqualityComparer<TKey>)Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to a specified key selector function and key comparer. (Defined by Enumerable.)
Public Extension MethodToDictionary<KeyValuePair<TKey, TValue>, TKey, TElement>(Func<KeyValuePair<TKey, TValue>, TKey>, Func<KeyValuePair<TKey, TValue>, TElement>)Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to specified key selector and element selector functions. (Defined by Enumerable.)
Public Extension MethodToDictionary<KeyValuePair<TKey, TValue>, TKey, TElement>(Func<KeyValuePair<TKey, TValue>, TKey>, Func<KeyValuePair<TKey, TValue>, TElement>, IEqualityComparer<TKey>)Overloaded. Creates a Dictionary<TKey, TValue> from an IEnumerable<T> according to a specified key selector function, a comparer, and an element selector function. (Defined by Enumerable.)
Public Extension MethodToList<KeyValuePair<TKey, TValue>>Creates a List<T> from an IEnumerable<T>. (Defined by Enumerable.)
Public Extension MethodToLookup<KeyValuePair<TKey, TValue>, TKey>(Func<KeyValuePair<TKey, TValue>, TKey>)Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to a specified key selector function. (Defined by Enumerable.)
Public Extension MethodToLookup<KeyValuePair<TKey, TValue>, TKey>(Func<KeyValuePair<TKey, TValue>, TKey>, IEqualityComparer<TKey>)Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to a specified key selector function and key comparer. (Defined by Enumerable.)
Public Extension MethodToLookup<KeyValuePair<TKey, TValue>, TKey, TElement>(Func<KeyValuePair<TKey, TValue>, TKey>, Func<KeyValuePair<TKey, TValue>, TElement>)Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to specified key selector and element selector functions. (Defined by Enumerable.)
Public Extension MethodToLookup<KeyValuePair<TKey, TValue>, TKey, TElement>(Func<KeyValuePair<TKey, TValue>, TKey>, Func<KeyValuePair<TKey, TValue>, TElement>, IEqualityComparer<TKey>)Overloaded. Creates a Lookup<TKey, TElement> from an IEnumerable<T> according to a specified key selector function, a comparer and an element selector function. (Defined by Enumerable.)
Public Extension MethodUnion<KeyValuePair<TKey, TValue>>(IEnumerable<KeyValuePair<TKey, TValue>>)Overloaded. Produces the set union of two sequences by using the default equality comparer. (Defined by Enumerable.)
Public Extension MethodUnion<KeyValuePair<TKey, TValue>>(IEnumerable<KeyValuePair<TKey, TValue>>, IEqualityComparer<KeyValuePair<TKey, TValue>>)Overloaded. Produces the set union of two sequences by using a specified IEqualityComparer<T>. (Defined by Enumerable.)
Public Extension MethodWhere<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Boolean>)Overloaded. Filters a sequence of values based on a predicate. (Defined by Enumerable.)
Public Extension MethodWhere<KeyValuePair<TKey, TValue>>(Func<KeyValuePair<TKey, TValue>, Int32, Boolean>)Overloaded. Filters a sequence of values based on a predicate. Each element's index is used in the logic of the predicate function. (Defined by Enumerable.)
Public Extension MethodZip<KeyValuePair<TKey, TValue>, TSecond, TResult>Merges two sequences by using the specified predicate function. (Defined by Enumerable.)
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  NameDescription
Explicit interface implemetationPrivate methodICollection<KeyValuePair<TKey, TValue>>.AddAdds the specified value to the ICollection<T> with the specified key.
Explicit interface implemetationPrivate methodICollection<KeyValuePair<TKey, TValue>>.ContainsDetermines whether the ICollection<T> contains a specific key and value.
Explicit interface implemetationPrivate methodICollection<KeyValuePair<TKey, TValue>>.CopyToCopies the elements of the ICollection<T> to an array of type KeyValuePair<TKey, TValue>, starting at the specified array index.
Explicit interface implemetationPrivate methodICollection.CopyToCopies the elements of the ICollection<T> to an array, starting at the specified array index.
Explicit interface implemetationPrivate propertyICollection<KeyValuePair<TKey, TValue>>.IsReadOnlyGets a value indicating whether the dictionary is read-only.
Explicit interface implemetationPrivate propertyICollection.IsSynchronizedGets a value indicating whether access to the ICollection is synchronized (thread safe).
Explicit interface implemetationPrivate methodICollection<KeyValuePair<TKey, TValue>>.RemoveRemoves a key and value from the dictionary.
Explicit interface implemetationPrivate propertyICollection.SyncRootGets an object that can be used to synchronize access to the ICollection.
Explicit interface implemetationPrivate methodIDictionary.AddAdds the specified key and value to the dictionary.
Explicit interface implemetationPrivate methodIDictionary.ContainsDetermines whether the IDictionary contains an element with the specified key.
Explicit interface implemetationPrivate methodIDictionary.GetEnumeratorReturns an IDictionaryEnumerator for the IDictionary.
Explicit interface implemetationPrivate propertyIDictionary.IsFixedSizeGets a value indicating whether the IDictionary has a fixed size.
Explicit interface implemetationPrivate propertyIDictionary.IsReadOnlyGets a value indicating whether the IDictionary is read-only.
Explicit interface implemetationPrivate propertyIDictionary.ItemGets or sets the value with the specified key.
Explicit interface implemetationPrivate propertyIDictionary<TKey, TValue>.KeysGets an ICollection<T> containing the keys of the IDictionary<TKey, TValue>.
Explicit interface implemetationPrivate propertyIDictionary.KeysGets an ICollection containing the keys of the IDictionary.
Explicit interface implemetationPrivate methodIDictionary.RemoveRemoves the element with the specified key from the IDictionary.
Explicit interface implemetationPrivate propertyIDictionary<TKey, TValue>.ValuesGets an ICollection<T> containing the values in the IDictionary<TKey, TValue>.
Explicit interface implemetationPrivate propertyIDictionary.ValuesGets an ICollection containing the values in the IDictionary.
Explicit interface implemetationPrivate methodIEnumerable<KeyValuePair<TKey, TValue>>.GetEnumeratorReturns an enumerator that iterates through the collection.
Explicit interface implemetationPrivate methodIEnumerable.GetEnumeratorReturns an enumerator that iterates through the collection.
Explicit interface implemetationPrivate propertyIReadOnlyDictionary<TKey, TValue>.KeysGets a collection containing the keys of the IReadOnlyDictionary<TKey, TValue>.
Explicit interface implemetationPrivate propertyIReadOnlyDictionary<TKey, TValue>.ValuesGets a collection containing the values of the IReadOnlyDictionary<TKey, TValue>.
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The Dictionary<TKey, TValue> generic class provides a mapping from a set of keys to a set of values. Each addition to the dictionary consists of a value and its associated key. Retrieving a value by using its key is very fast, close to O(1), because the Dictionary<TKey, TValue> class is implemented as a hash table.

NoteNote:

The speed of retrieval depends on the quality of the hashing algorithm of the type specified for TKey.

As long as an object is used as a key in the Dictionary<TKey, TValue>, it must not change in any way that affects its hash value. Every key in a Dictionary<TKey, TValue> must be unique according to the dictionary's equality comparer. A key cannot be null, but a value can be, if the value type TValue is a reference type.

Dictionary<TKey, TValue> requires an equality implementation to determine whether keys are equal. You can specify an implementation of the IEqualityComparer<T> generic interface by using a constructor that accepts a comparer parameter; if you do not specify an implementation, the default generic equality comparer EqualityComparer<T>.Default is used. If type TKey implements the System.IEquatable<T> generic interface, the default equality comparer uses that implementation.

NoteNote:

For example, you can use the case-insensitive string comparers provided by the StringComparer class to create dictionaries with case-insensitive string keys.

The capacity of a Dictionary<TKey, TValue> is the number of elements the Dictionary<TKey, TValue> can hold. As elements are added to a Dictionary<TKey, TValue>, the capacity is automatically increased as required by reallocating the internal array.

For purposes of enumeration, each item in the dictionary is treated as a KeyValuePair<TKey, TValue> structure representing a value and its key. The order in which the items are returned is undefined.

The foreach statement of the C# language (for each in C++, For Each in Visual Basic) requires the type of each element in the collection. Since the Dictionary<TKey, TValue> is a collection of keys and values, the element type is not the type of the key or the type of the value. Instead, the element type is a KeyValuePair<TKey, TValue> of the key type and the value type. For example:

foreach (KeyValuePair<int, string> kvp in myDictionary) {...}

The foreach statement is a wrapper around the enumerator, which allows only reading from the collection, not writing to it.

NoteNote:

Because keys can be inherited and their behavior changed, their absolute uniqueness cannot be guaranteed by comparisons using the Equals method.

Version Notes

Windows Phone

 An exception is thrown when deriving a class from Dictionary where the TKey parameter is an enumeration.

There are two examples for this class. This first example uses a Dictionary<TKey, TValue> object to contain cast member information for the play "Othello". The names of the characters are the keys of the dictionary and the names of the actors are the values of the dictionary. This dictionary (OthelloDict) is contained in a class (OthelloCast) that is derived from a List<T> class. The constructor for the OthelloCast object populates its list with the keys of the OthelloDict dictionary. The OthelloCast object is bound to a ListBox control. The binding in this example is one-way; see Data binding for Windows Phone 8 for a discussion of other binding options and scenarios.

The following code shows the OthelloCast class. Add this class to the partial Page class of your project.


// Make sure this class is
// within the C# namespace.
public class OthelloCast : List<string>
{
    // Use a dictionary to contain
    // cast names (key) and actor names (value).
    public Dictionary<string, string> OthelloDict =
        new Dictionary<string, string>();

    public OthelloCast()
    {
        // Add data to the dictionary.
        OthelloDict.Add("Bianca", "Gretchen Rivas");
        OthelloDict.Add("Brabantio", "Carlos Lacerda");
        OthelloDict.Add("Cassio", "Steve Masters");
        OthelloDict.Add("Clown", "Michael Ludwig");
        OthelloDict.Add("Desdemona", "Catherine Autier Miconi");
        OthelloDict.Add("Duke of Venice", "Ken Circeo");
        OthelloDict.Add("Emilia", "Eva Valverde");
        OthelloDict.Add("Gratiano", "Akos Kozari");
        OthelloDict.Add("Iago", "Darius Stasevicius");
        OthelloDict.Add("Lodovico", "Fernando Souza");
        OthelloDict.Add("Montano", "Jeff Hay");
        OthelloDict.Add("Othello", "Marco Tanara");
        OthelloDict.Add("Roderigo", "Pedro Ruivo");

        // Populate the list with character names.
        foreach (KeyValuePair<string, string> kvp in OthelloDict)
        {
            this.Add(kvp.Key);
        }
    }
}


When you select a character in the ListBox control, the actor who plays that character is displayed in a TextBlock control. The following code shows how this is done by the event handler for the SelectionChanged event for the ListBox control. Add this handler to the partial Page class. For information on how to compile and run this example code, see Building examples that have static TextBlock controls for Windows Phone 8.


private void ListCharacters_SelectionChanged(object sender,
    SelectionChangedEventArgs e)
{
    // Create an instance of OthelloCast to
    // look up an actor by their character.
    OthelloCast othello = new OthelloCast();

    // Get the selected character name (key).
    string key = ListCharacters.SelectedItem.ToString();

    // Get the key's value (actor name) and display it.
    ShowActor.Text = othello.OthelloDict[key].ToString();
}


The following XAML references and elements perform the data binding:

  • xmlns:my="clr-namespace:CastMembers"

    This is a reference to the common language runtime (CLR) namespace, which is automatically declared within the assembly and exposes its public types. Replace CsatMembers with the name of your assembly (project name).

  • <my:OthelloCast x:Name="Characters"/>

    This is a resource dictionary reference specified in the <Grid.Resources> element. It specifies the object to bind to (OthelloCast) and its name (Characters) is specified by controls, such as a ListBox control, that use this resource.

  • <ListBox Margin ="5,5,5,5" SelectionChanged="ListCharacters_SelectionChanged" Grid.Row="1" Grid.Column="0" x:Name="ListCharacters" ItemsSource="{Binding Source={StaticResource Characters}}"/>

    This element defines a ListBox control with the ItemsSource property set to the bound object. Note that it includes the event handler defined for the SelectionChanged event.

The complete XAML is as follows. For information on how to compile and run this example code, see Building examples that have static TextBlock controls for Windows Phone 8.


 <UserControl x:Class="CastMembers.Page"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:my="clr-namespace:CastMembers"
    Width="400" Height="400">
    <Grid x:Name="LayoutRoot" Background="White" ShowGridLines="False">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition Width="Auto"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>
        <Grid.Resources>
            <my:OthelloCast x:Name="Characters"/>
        </Grid.Resources>
        <TextBlock Margin ="5,5,5,5" Grid.Row="0" Grid.Column="0" Text="Othello Cast:" FontWeight="Bold" />
        <ListBox Margin ="5,5,5,5" SelectionChanged="ListCharacters_SelectionChanged" Grid.Row="1" Grid.Column="0" x:Name="ListCharacters"  ItemsSource="{Binding Source={StaticResource Characters}}"/>
        <TextBlock Margin ="5,5,5,5" Grid.Row="0" Grid.Column="1" Text="Actor:" FontWeight="Bold" />
        <TextBlock Margin ="5,5,5,5" Grid.Row="1" Grid.Column="1" x:Name="ShowActor" Text=""/> 
    </Grid>
</UserControl>


The next example creates an empty Dictionary<TKey, TValue> of strings with string keys and uses the Add method to add some elements. The example demonstrates that the Add method throws an ArgumentException when attempting to add a duplicate key.

The example uses the Item property (the indexer in C#) to retrieve values, demonstrating that a KeyNotFoundException is thrown when a requested key is not present, and showing that the value associated with a key can be replaced.

The example shows how to use the TryGetValue method as a more efficient way to retrieve values if a program often must try key values that are not in the dictionary, and it shows how to use the ContainsKey method to test whether a key exists before calling the Add method.

The example shows how to enumerate the keys and values in the dictionary and how to enumerate the keys and values alone using the Keys property and the Values property.

Finally, the example demonstrates the Remove method.


using System;
using System.Collections.Generic;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      // Create a new dictionary of strings, with string keys.
      //
      Dictionary<string, string> openWith =
          new Dictionary<string, string>();

      // Add some elements to the dictionary. There are no 
      // duplicate keys, but some of the values are duplicates.
      openWith.Add("txt", "notepad.exe");
      openWith.Add("bmp", "paint.exe");
      openWith.Add("dib", "paint.exe");
      openWith.Add("rtf", "wordpad.exe");

      // The Add method throws an exception if the new key is 
      // already in the dictionary.
      try
      {
         openWith.Add("txt", "winword.exe");
      }
      catch (ArgumentException)
      {
         outputBlock.Text += "An element with Key = \"txt\" already exists." + "\n";
      }

      // The Item property is another name for the indexer, so you 
      // can omit its name when accessing elements. 
      outputBlock.Text += String.Format("For key = \"rtf\", value = {0}.",
          openWith["rtf"]) + "\n";

      // The indexer can be used to change the value associated
      // with a key.
      openWith["rtf"] = "winword.exe";
      outputBlock.Text += String.Format("For key = \"rtf\", value = {0}.",
          openWith["rtf"]) + "\n";

      // If a key does not exist, setting the indexer for that key
      // adds a new key/value pair.
      openWith["doc"] = "winword.exe";

      // The indexer throws an exception if the requested key is
      // not in the dictionary.
      try
      {
         outputBlock.Text += String.Format("For key = \"tif\", value = {0}.",
             openWith["tif"]) + "\n";
      }
      catch (KeyNotFoundException)
      {
         outputBlock.Text += "Key = \"tif\" is not found." + "\n";
      }

      // When a program often has to try keys that turn out not to
      // be in the dictionary, TryGetValue can be a more efficient 
      // way to retrieve values.
      string value = "";
      if (openWith.TryGetValue("tif", out value))
      {
         outputBlock.Text += String.Format("For key = \"tif\", value = {0}.", value) + "\n";
      }
      else
      {
         outputBlock.Text += "Key = \"tif\" is not found." + "\n";
      }

      // ContainsKey can be used to test keys before inserting 
      // them.
      if (!openWith.ContainsKey("ht"))
      {
         openWith.Add("ht", "hypertrm.exe");
         outputBlock.Text += String.Format("Value added for key = \"ht\": {0}",
             openWith["ht"]) + "\n";
      }

      // When you use foreach to enumerate dictionary elements,
      // the elements are retrieved as KeyValuePair objects.
      outputBlock.Text += "\n";
      foreach (KeyValuePair<string, string> kvp in openWith)
      {
         outputBlock.Text += String.Format("Key = {0}, Value = {1}",
             kvp.Key, kvp.Value) + "\n";
      }

      // To get the values alone, use the Values property.
      Dictionary<string, string>.ValueCollection valueColl =
          openWith.Values;

      // The elements of the ValueCollection are strongly typed
      // with the type that was specified for dictionary values.
      outputBlock.Text += "\n";
      foreach (string s in valueColl)
      {
         outputBlock.Text += String.Format("Value = {0}", s) + "\n";
      }

      // To get the keys alone, use the Keys property.
      Dictionary<string, string>.KeyCollection keyColl =
          openWith.Keys;

      // The elements of the KeyCollection are strongly typed
      // with the type that was specified for dictionary keys.
      outputBlock.Text += "\n";
      foreach (string s in keyColl)
      {
         outputBlock.Text += String.Format("Key = {0}", s) + "\n";
      }

      // Use the Remove method to remove a key/value pair.
      outputBlock.Text += "\nRemove(\"doc\")" + "\n";
      openWith.Remove("doc");

      if (!openWith.ContainsKey("doc"))
      {
         outputBlock.Text += "Key \"doc\" is not found." + "\n";
      }
   }
}

/* This code example produces the following output:

An element with Key = "txt" already exists.
For key = "rtf", value = wordpad.exe.
For key = "rtf", value = winword.exe.
Key = "tif" is not found.
Key = "tif" is not found.
Value added for key = "ht": hypertrm.exe

Key = txt, Value = notepad.exe
Key = bmp, Value = paint.exe
Key = dib, Value = paint.exe
Key = rtf, Value = winword.exe
Key = doc, Value = winword.exe
Key = ht, Value = hypertrm.exe

Value = notepad.exe
Value = paint.exe
Value = paint.exe
Value = winword.exe
Value = winword.exe
Value = hypertrm.exe

Key = txt
Key = bmp
Key = dib
Key = rtf
Key = doc
Key = ht

Remove("doc")
Key "doc" is not found.
 */


Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Windows Phone

Public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

A Dictionary<TKey, TValue> can support multiple readers concurrently, as long as the collection is not modified. Even so, enumerating through a collection is intrinsically not a thread-safe procedure. In the rare case where an enumeration contends with write accesses, the collection must be locked during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization.

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