# ReadOnlyCollection(Of T) Class

**.NET Framework 4.5**

Provides the base class for a generic read-only collection.

System.Collections.ObjectModel.ReadOnlyCollection(Of T)

System.Collections.ObjectModel.ReadOnlyObservableCollection(Of T)

System.Data.Metadata.Edm.ReadOnlyMetadataCollection(Of T)

System.Security.Cryptography.ManifestSignatureInformationCollection

System.ServiceModel.Channels.AddressHeaderCollection

System.Windows.Input.StylusButtonCollection

System.Windows.Input.StylusDeviceCollection

**Namespace:**System.Collections.ObjectModel

**Assembly:**mscorlib (in mscorlib.dll)

'Declaration <SerializableAttribute> _ <ComVisibleAttribute(False)> _ Public Class ReadOnlyCollection(Of T) _ Implements IList(Of T), ICollection(Of T), _ IList, ICollection, IReadOnlyList(Of T), IReadOnlyCollection(Of T), _ IEnumerable(Of T), IEnumerable

#### Type Parameters

- T
The type of elements in the collection.

The ReadOnlyCollection(Of T) type exposes the following members.

Name | Description | |
---|---|---|

ReadOnlyCollection(Of T) | Initializes a new instance of the ReadOnlyCollection(Of T) class that is a read-only wrapper around the specified list. |

Name | Description | |
---|---|---|

Count | Gets the number of elements contained in the ReadOnlyCollection(Of T) instance. | |

Item | Gets the element at the specified index. | |

Items | Returns the IList(Of T) that the ReadOnlyCollection(Of T) wraps. |

Name | Description | |
---|---|---|

Contains | Determines whether an element is in the ReadOnlyCollection(Of T). | |

CopyTo | Copies the entire ReadOnlyCollection(Of T) to a compatible one-dimensional Array, starting at the specified index of the target array. | |

Equals(Object) | Determines whether the specified object is equal to the current object. (Inherited from Object.) | |

Finalize | Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.) | |

GetEnumerator | Returns an enumerator that iterates through the ReadOnlyCollection(Of T). | |

GetHashCode | Serves as the default hash function. (Inherited from Object.) | |

GetType | Gets the Type of the current instance. (Inherited from Object.) | |

IndexOf | Searches for the specified object and returns the zero-based index of the first occurrence within the entire ReadOnlyCollection(Of T). | |

MemberwiseClone | Creates a shallow copy of the current Object. (Inherited from Object.) | |

ToString | Returns a string that represents the current object. (Inherited from Object.) |

Name | Description | |
---|---|---|

Aggregate(Of T)(Func(Of T, T, T)) | Overloaded. Applies an accumulator function over a sequence. (Defined by Enumerable.) | |

Aggregate(Of T, TAccumulate)(TAccumulate, Func(Of TAccumulate, T, TAccumulate)) | Overloaded. Applies an accumulator function over a sequence. The specified seed value is used as the initial accumulator value. (Defined by Enumerable.) | |

Aggregate(Of T, TAccumulate, TResult)(TAccumulate, Func(Of TAccumulate, T, TAccumulate), Func(Of 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.) | |

All(Of T) | Determines whether all elements of a sequence satisfy a condition. (Defined by Enumerable.) | |

Any(Of T) | Overloaded. Determines whether a sequence contains any elements. (Defined by Enumerable.) | |

Any(Of T)(Func(Of T, Boolean)) | Overloaded. Determines whether any element of a sequence satisfies a condition. (Defined by Enumerable.) | |

AsEnumerable(Of T) | Returns the input typed as IEnumerable(Of T). (Defined by Enumerable.) | |

AsParallel | Overloaded. Enables parallelization of a query. (Defined by ParallelEnumerable.) | |

AsParallel(Of T) | Overloaded. Enables parallelization of a query. (Defined by ParallelEnumerable.) | |

AsQueryable | Overloaded. Converts an IEnumerable to an IQueryable. (Defined by Queryable.) | |

AsQueryable(Of T) | Overloaded. Converts a generic IEnumerable(Of T) to a generic IQueryable(Of T). (Defined by Queryable.) | |

Average(Of T)(Func(Of T, 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.) | |

Average(Of T)(Func(Of T, Nullable(Of 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.) | |

Average(Of T)(Func(Of T, 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.) | |

Average(Of T)(Func(Of T, Nullable(Of 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.) | |

Average(Of T)(Func(Of T, 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.) | |

Average(Of T)(Func(Of T, Nullable(Of 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.) | |

Average(Of T)(Func(Of T, 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.) | |

Average(Of T)(Func(Of T, Nullable(Of 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.) | |

Average(Of T)(Func(Of T, 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.) | |

Average(Of T)(Func(Of T, Nullable(Of 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.) | |

Cast(Of TResult) | Casts the elements of an IEnumerable to the specified type. (Defined by Enumerable.) | |

Concat(Of T) | Concatenates two sequences. (Defined by Enumerable.) | |

Contains(Of T)(T) | Overloaded. Determines whether a sequence contains a specified element by using the default equality comparer. (Defined by Enumerable.) | |

Contains(Of T)(T, IEqualityComparer(Of T)) | Overloaded. Determines whether a sequence contains a specified element by using a specified IEqualityComparer(Of T). (Defined by Enumerable.) | |

Count(Of T) | Overloaded. Returns the number of elements in a sequence. (Defined by Enumerable.) | |

Count(Of T)(Func(Of T, Boolean)) | Overloaded. Returns a number that represents how many elements in the specified sequence satisfy a condition. (Defined by Enumerable.) | |

DefaultIfEmpty(Of T) | 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.) | |

DefaultIfEmpty(Of T)(T) | Overloaded. Returns the elements of the specified sequence or the specified value in a singleton collection if the sequence is empty. (Defined by Enumerable.) | |

Distinct(Of T) | Overloaded. Returns distinct elements from a sequence by using the default equality comparer to compare values. (Defined by Enumerable.) | |

Distinct(Of T)(IEqualityComparer(Of T)) | Overloaded. Returns distinct elements from a sequence by using a specified IEqualityComparer(Of T) to compare values. (Defined by Enumerable.) | |

ElementAt(Of T) | Returns the element at a specified index in a sequence. (Defined by Enumerable.) | |

ElementAtOrDefault(Of T) | Returns the element at a specified index in a sequence or a default value if the index is out of range. (Defined by Enumerable.) | |

Except(Of T)(IEnumerable(Of T)) | Overloaded. Produces the set difference of two sequences by using the default equality comparer to compare values. (Defined by Enumerable.) | |

Except(Of T)(IEnumerable(Of T), IEqualityComparer(Of T)) | Overloaded. Produces the set difference of two sequences by using the specified IEqualityComparer(Of T) to compare values. (Defined by Enumerable.) | |

First(Of T) | Overloaded. Returns the first element of a sequence. (Defined by Enumerable.) | |

First(Of T)(Func(Of T, Boolean)) | Overloaded. Returns the first element in a sequence that satisfies a specified condition. (Defined by Enumerable.) | |

FirstOrDefault(Of T) | Overloaded. Returns the first element of a sequence, or a default value if the sequence contains no elements. (Defined by Enumerable.) | |

FirstOrDefault(Of T)(Func(Of T, 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.) | |

GroupBy(Of T, TKey)(Func(Of T, TKey)) | Overloaded. Groups the elements of a sequence according to a specified key selector function. (Defined by Enumerable.) | |

GroupBy(Of T, TKey)(Func(Of T, TKey), IEqualityComparer(Of 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.) | |

GroupBy(Of T, TKey, TElement)(Func(Of T, TKey), Func(Of T, 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.) | |

GroupBy(Of T, TKey, TResult)(Func(Of T, TKey), Func(Of TKey, IEnumerable(Of T), 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.) | |

GroupBy(Of T, TKey, TElement)(Func(Of T, TKey), Func(Of T, TElement), IEqualityComparer(Of 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.) | |

GroupBy(Of T, TKey, TResult)(Func(Of T, TKey), Func(Of TKey, IEnumerable(Of T), TResult), IEqualityComparer(Of 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.) | |

GroupBy(Of T, TKey, TElement, TResult)(Func(Of T, TKey), Func(Of T, TElement), Func(Of TKey, IEnumerable(Of 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.) | |

GroupBy(Of T, TKey, TElement, TResult)(Func(Of T, TKey), Func(Of T, TElement), Func(Of TKey, IEnumerable(Of TElement), TResult), IEqualityComparer(Of 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.) | |

GroupJoin(Of T, TInner, TKey, TResult)(IEnumerable(Of TInner), Func(Of T, TKey), Func(Of TInner, TKey), Func(Of T, IEnumerable(Of 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.) | |

GroupJoin(Of T, TInner, TKey, TResult)(IEnumerable(Of TInner), Func(Of T, TKey), Func(Of TInner, TKey), Func(Of T, IEnumerable(Of TInner), TResult), IEqualityComparer(Of TKey)) | Overloaded. Correlates the elements of two sequences based on key equality and groups the results. A specified IEqualityComparer(Of T) is used to compare keys. (Defined by Enumerable.) | |

Intersect(Of T)(IEnumerable(Of T)) | Overloaded. Produces the set intersection of two sequences by using the default equality comparer to compare values. (Defined by Enumerable.) | |

Intersect(Of T)(IEnumerable(Of T), IEqualityComparer(Of T)) | Overloaded. Produces the set intersection of two sequences by using the specified IEqualityComparer(Of T) to compare values. (Defined by Enumerable.) | |

Join(Of T, TInner, TKey, TResult)(IEnumerable(Of TInner), Func(Of T, TKey), Func(Of TInner, TKey), Func(Of T, 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.) | |

Join(Of T, TInner, TKey, TResult)(IEnumerable(Of TInner), Func(Of T, TKey), Func(Of TInner, TKey), Func(Of T, TInner, TResult), IEqualityComparer(Of TKey)) | Overloaded. Correlates the elements of two sequences based on matching keys. A specified IEqualityComparer(Of T) is used to compare keys. (Defined by Enumerable.) | |

Last(Of T) | Overloaded. Returns the last element of a sequence. (Defined by Enumerable.) | |

Last(Of T)(Func(Of T, Boolean)) | Overloaded. Returns the last element of a sequence that satisfies a specified condition. (Defined by Enumerable.) | |

LastOrDefault(Of T) | Overloaded. Returns the last element of a sequence, or a default value if the sequence contains no elements. (Defined by Enumerable.) | |

LastOrDefault(Of T)(Func(Of T, 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.) | |

LongCount(Of T) | Overloaded. Returns an Int64 that represents the total number of elements in a sequence. (Defined by Enumerable.) | |

LongCount(Of T)(Func(Of T, Boolean)) | Overloaded. Returns an Int64 that represents how many elements in a sequence satisfy a condition. (Defined by Enumerable.) | |

Max(Of T) | Overloaded. Returns the maximum value in a generic sequence. (Defined by Enumerable.) | |

Max(Of T)(Func(Of T, Decimal)) | Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Decimal value. (Defined by Enumerable.) | |

Max(Of T)(Func(Of T, Nullable(Of Decimal))) | Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Decimal value. (Defined by Enumerable.) | |

Max(Of T)(Func(Of T, Double)) | Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Double value. (Defined by Enumerable.) | |

Max(Of T)(Func(Of T, Nullable(Of Double))) | Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Double value. (Defined by Enumerable.) | |

Max(Of T)(Func(Of T, Int32)) | Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Int32 value. (Defined by Enumerable.) | |

Max(Of T)(Func(Of T, Nullable(Of Int32))) | Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Int32 value. (Defined by Enumerable.) | |

Max(Of T)(Func(Of T, Int64)) | Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Int64 value. (Defined by Enumerable.) | |

Max(Of T)(Func(Of T, Nullable(Of Int64))) | Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Int64 value. (Defined by Enumerable.) | |

Max(Of T)(Func(Of T, Single)) | Overloaded. Invokes a transform function on each element of a sequence and returns the maximum Single value. (Defined by Enumerable.) | |

Max(Of T)(Func(Of T, Nullable(Of Single))) | Overloaded. Invokes a transform function on each element of a sequence and returns the maximum nullable Single value. (Defined by Enumerable.) | |

Max(Of T, TResult)(Func(Of T, TResult)) | Overloaded. Invokes a transform function on each element of a generic sequence and returns the maximum resulting value. (Defined by Enumerable.) | |

Min(Of T) | Overloaded. Returns the minimum value in a generic sequence. (Defined by Enumerable.) | |

Min(Of T)(Func(Of T, Decimal)) | Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Decimal value. (Defined by Enumerable.) | |

Min(Of T)(Func(Of T, Nullable(Of Decimal))) | Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Decimal value. (Defined by Enumerable.) | |

Min(Of T)(Func(Of T, Double)) | Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Double value. (Defined by Enumerable.) | |

Min(Of T)(Func(Of T, Nullable(Of Double))) | Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Double value. (Defined by Enumerable.) | |

Min(Of T)(Func(Of T, Int32)) | Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Int32 value. (Defined by Enumerable.) | |

Min(Of T)(Func(Of T, Nullable(Of Int32))) | Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Int32 value. (Defined by Enumerable.) | |

Min(Of T)(Func(Of T, Int64)) | Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Int64 value. (Defined by Enumerable.) | |

Min(Of T)(Func(Of T, Nullable(Of Int64))) | Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Int64 value. (Defined by Enumerable.) | |

Min(Of T)(Func(Of T, Single)) | Overloaded. Invokes a transform function on each element of a sequence and returns the minimum Single value. (Defined by Enumerable.) | |

Min(Of T)(Func(Of T, Nullable(Of Single))) | Overloaded. Invokes a transform function on each element of a sequence and returns the minimum nullable Single value. (Defined by Enumerable.) | |

Min(Of T, TResult)(Func(Of T, TResult)) | Overloaded. Invokes a transform function on each element of a generic sequence and returns the minimum resulting value. (Defined by Enumerable.) | |

OfType(Of TResult) | Filters the elements of an IEnumerable based on a specified type. (Defined by Enumerable.) | |

OrderBy(Of T, TKey)(Func(Of T, TKey)) | Overloaded. Sorts the elements of a sequence in ascending order according to a key. (Defined by Enumerable.) | |

OrderBy(Of T, TKey)(Func(Of T, TKey), IComparer(Of TKey)) | Overloaded. Sorts the elements of a sequence in ascending order by using a specified comparer. (Defined by Enumerable.) | |

OrderByDescending(Of T, TKey)(Func(Of T, TKey)) | Overloaded. Sorts the elements of a sequence in descending order according to a key. (Defined by Enumerable.) | |

OrderByDescending(Of T, TKey)(Func(Of T, TKey), IComparer(Of TKey)) | Overloaded. Sorts the elements of a sequence in descending order by using a specified comparer. (Defined by Enumerable.) | |

Reverse(Of T) | Inverts the order of the elements in a sequence. (Defined by Enumerable.) | |

Select(Of T, TResult)(Func(Of T, TResult)) | Overloaded. Projects each element of a sequence into a new form. (Defined by Enumerable.) | |

Select(Of T, TResult)(Func(Of T, Int32, TResult)) | Overloaded. Projects each element of a sequence into a new form by incorporating the element's index. (Defined by Enumerable.) | |

SelectMany(Of T, TResult)(Func(Of T, IEnumerable(Of TResult))) | Overloaded. Projects each element of a sequence to an IEnumerable(Of T) and flattens the resulting sequences into one sequence. (Defined by Enumerable.) | |

SelectMany(Of T, TResult)(Func(Of T, Int32, IEnumerable(Of TResult))) | Overloaded. Projects each element of a sequence to an IEnumerable(Of 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.) | |

SelectMany(Of T, TCollection, TResult)(Func(Of T, Int32, IEnumerable(Of TCollection)), Func(Of T, TCollection, TResult)) | Overloaded. Projects each element of a sequence to an IEnumerable(Of 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.) | |

SelectMany(Of T, TCollection, TResult)(Func(Of T, IEnumerable(Of TCollection)), Func(Of T, TCollection, TResult)) | Overloaded. Projects each element of a sequence to an IEnumerable(Of T), flattens the resulting sequences into one sequence, and invokes a result selector function on each element therein. (Defined by Enumerable.) | |

SequenceEqual(Of T)(IEnumerable(Of T)) | Overloaded. Determines whether two sequences are equal by comparing the elements by using the default equality comparer for their type. (Defined by Enumerable.) | |

SequenceEqual(Of T)(IEnumerable(Of T), IEqualityComparer(Of T)) | Overloaded. Determines whether two sequences are equal by comparing their elements by using a specified IEqualityComparer(Of T). (Defined by Enumerable.) | |

Single(Of T) | 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.) | |

Single(Of T)(Func(Of T, 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.) | |

SingleOrDefault(Of T) | 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.) | |

SingleOrDefault(Of T)(Func(Of T, 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.) | |

Skip(Of T) | Bypasses a specified number of elements in a sequence and then returns the remaining elements. (Defined by Enumerable.) | |

SkipWhile(Of T)(Func(Of T, Boolean)) | Overloaded. Bypasses elements in a sequence as long as a specified condition is true and then returns the remaining elements. (Defined by Enumerable.) | |

SkipWhile(Of T)(Func(Of T, 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.) | |

Sum(Of T)(Func(Of T, 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.) | |

Sum(Of T)(Func(Of T, Nullable(Of 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.) | |

Sum(Of T)(Func(Of T, 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.) | |

Sum(Of T)(Func(Of T, Nullable(Of 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.) | |

Sum(Of T)(Func(Of T, 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.) | |

Sum(Of T)(Func(Of T, Nullable(Of 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.) | |

Sum(Of T)(Func(Of T, 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.) | |

Sum(Of T)(Func(Of T, Nullable(Of 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.) | |

Sum(Of T)(Func(Of T, 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.) | |

Sum(Of T)(Func(Of T, Nullable(Of 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.) | |

Take(Of T) | Returns a specified number of contiguous elements from the start of a sequence. (Defined by Enumerable.) | |

TakeWhile(Of T)(Func(Of T, Boolean)) | Overloaded. Returns elements from a sequence as long as a specified condition is true. (Defined by Enumerable.) | |

TakeWhile(Of T)(Func(Of T, 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.) | |

ToArray(Of T) | Creates an array from a IEnumerable(Of T). (Defined by Enumerable.) | |

ToDictionary(Of T, TKey)(Func(Of T, TKey)) | Overloaded. Creates a Dictionary(Of TKey, TValue) from an IEnumerable(Of T) according to a specified key selector function. (Defined by Enumerable.) | |

ToDictionary(Of T, TKey)(Func(Of T, TKey), IEqualityComparer(Of TKey)) | Overloaded. Creates a Dictionary(Of TKey, TValue) from an IEnumerable(Of T) according to a specified key selector function and key comparer. (Defined by Enumerable.) | |

ToDictionary(Of T, TKey, TElement)(Func(Of T, TKey), Func(Of T, TElement)) | Overloaded. Creates a Dictionary(Of TKey, TValue) from an IEnumerable(Of T) according to specified key selector and element selector functions. (Defined by Enumerable.) | |

ToDictionary(Of T, TKey, TElement)(Func(Of T, TKey), Func(Of T, TElement), IEqualityComparer(Of TKey)) | Overloaded. Creates a Dictionary(Of TKey, TValue) from an IEnumerable(Of T) according to a specified key selector function, a comparer, and an element selector function. (Defined by Enumerable.) | |

ToList(Of T) | Creates a List(Of T) from an IEnumerable(Of T). (Defined by Enumerable.) | |

ToLookup(Of T, TKey)(Func(Of T, TKey)) | Overloaded. Creates a Lookup(Of TKey, TElement) from an IEnumerable(Of T) according to a specified key selector function. (Defined by Enumerable.) | |

ToLookup(Of T, TKey)(Func(Of T, TKey), IEqualityComparer(Of TKey)) | Overloaded. Creates a Lookup(Of TKey, TElement) from an IEnumerable(Of T) according to a specified key selector function and key comparer. (Defined by Enumerable.) | |

ToLookup(Of T, TKey, TElement)(Func(Of T, TKey), Func(Of T, TElement)) | Overloaded. Creates a Lookup(Of TKey, TElement) from an IEnumerable(Of T) according to specified key selector and element selector functions. (Defined by Enumerable.) | |

ToLookup(Of T, TKey, TElement)(Func(Of T, TKey), Func(Of T, TElement), IEqualityComparer(Of TKey)) | Overloaded. Creates a Lookup(Of TKey, TElement) from an IEnumerable(Of T) according to a specified key selector function, a comparer and an element selector function. (Defined by Enumerable.) | |

Union(Of T)(IEnumerable(Of T)) | Overloaded. Produces the set union of two sequences by using the default equality comparer. (Defined by Enumerable.) | |

Union(Of T)(IEnumerable(Of T), IEqualityComparer(Of T)) | Overloaded. Produces the set union of two sequences by using a specified IEqualityComparer(Of T). (Defined by Enumerable.) | |

Where(Of T)(Func(Of T, Boolean)) | Overloaded. Filters a sequence of values based on a predicate. (Defined by Enumerable.) | |

Where(Of T)(Func(Of T, 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.) | |

Zip(Of T, TSecond, TResult) | Applies a specified function to the corresponding elements of two sequences, producing a sequence of the results. (Defined by Enumerable.) |

Name | Description | |
---|---|---|

ICollection(Of T).Add | Adds an item to the ICollection(Of T). This implementation always throws NotSupportedException. | |

ICollection(Of T).Clear | Removes all items from the ICollection(Of T). This implementation always throws NotSupportedException. | |

ICollection.CopyTo | Copies the elements of the ICollection to an Array, starting at a particular Array index. | |

ICollection(Of T).IsReadOnly | Gets a value indicating whether the ICollection(Of T) is read-only. | |

ICollection.IsSynchronized | Gets a value indicating whether access to the ICollection is synchronized (thread safe). | |

ICollection(Of T).Remove | Removes the first occurrence of a specific object from the ICollection(Of T). This implementation always throws NotSupportedException. | |

ICollection.SyncRoot | Gets an object that can be used to synchronize access to the ICollection. | |

IEnumerable.GetEnumerator | Returns an enumerator that iterates through a collection. | |

IList.Add | Adds an item to the IList. This implementation always throws NotSupportedException. | |

IList.Clear | Removes all items from the IList. This implementation always throws NotSupportedException. | |

IList.Contains | Determines whether the IList contains a specific value. | |

IList.IndexOf | Determines the index of a specific item in the IList. | |

IList(Of T).Insert | Inserts an item to the IList(Of T) at the specified index. This implementation always throws NotSupportedException. | |

IList.Insert | Inserts an item to the IList at the specified index. This implementation always throws NotSupportedException. | |

IList.IsFixedSize | Gets a value indicating whether the IList has a fixed size. | |

IList.IsReadOnly | Gets a value indicating whether the IList is read-only. | |

IList(Of T).Item | Gets the element at the specified index. An NotSupportedException occurs if you try to set the item at the specified index. | |

IList.Item | Gets the element at the specified index. A NotSupportedException occurs if you try to set the item at the specified index. | |

IList.Remove | Removes the first occurrence of a specific object from the IList. This implementation always throws NotSupportedException. | |

IList(Of T).RemoveAt | Removes the IList(Of T) item at the specified index. This implementation always throws NotSupportedException. | |

IList.RemoveAt | Removes the IList item at the specified index. This implementation always throws NotSupportedException. |

An instance of the ReadOnlyCollection(Of T) generic class is always read-only. A collection that is read-only is simply a collection with a wrapper that prevents modifying the collection; therefore, if changes are made to the underlying collection, the read-only collection reflects those changes. See Collection(Of T) for a modifiable version of this class.

Notes to ImplementersThis base class is provided to make it easier for implementers to create a generic read-only custom collection. Implementers are encouraged to extend this base class instead of creating their own.

The following code example demonstrates several members of the ReadOnlyCollection(Of T) class. The code example creates a List(Of T) of strings and adds four dinosaur names to it. The code example then wraps the list in a ReadOnlyCollection(Of T).

After demonstrating the Count, Contains, Item, and IList.IndexOf members, the code example shows that the ReadOnlyCollection(Of T) is just a wrapper for the original List(Of T) by adding a new item to the List(Of T) and displaying the contents of the ReadOnlyCollection(Of T).

Finally, the code example creates an array larger than the collection and uses the CopyTo method to insert the elements of the collection into the middle of the array.

Imports System Imports System.Collections.Generic Imports System.Collections.ObjectModel Public Class Example Public Shared Sub Main() Dim dinosaurs As New List(Of String) dinosaurs.Add("Tyrannosaurus") dinosaurs.Add("Amargasaurus") dinosaurs.Add("Deinonychus") dinosaurs.Add("Compsognathus") Dim readOnlyDinosaurs As _ New ReadOnlyCollection(Of String)(dinosaurs) Console.WriteLine() For Each dinosaur As String In readOnlyDinosaurs Console.WriteLine(dinosaur) Next Console.WriteLine(vbLf & "Count: {0}", _ readOnlyDinosaurs.Count) Console.WriteLine(vbLf & "Contains(""Deinonychus""): {0}", _ readOnlyDinosaurs.Contains("Deinonychus")) Console.WriteLine(vbLf & _ "readOnlyDinosaurs(3): {0}", readOnlyDinosaurs(3)) Console.WriteLine(vbLf & "IndexOf(""Compsognathus""): {0}", _ readOnlyDinosaurs.IndexOf("Compsognathus")) Console.WriteLine(vbLf & "Insert into the wrapped List:") Console.WriteLine("Insert(2, ""Oviraptor"")") dinosaurs.Insert(2, "Oviraptor") Console.WriteLine() For Each dinosaur As String In readOnlyDinosaurs Console.WriteLine(dinosaur) Next Dim dinoArray(readOnlyDinosaurs.Count + 1) As String readOnlyDinosaurs.CopyTo(dinoArray, 1) Console.WriteLine(vbLf & "Copied array has {0} elements:", _ dinoArray.Length) For Each dinosaur As String In dinoArray Console.WriteLine("""{0}""", dinosaur) Next End Sub End Class ' This code example produces the following output: ' 'Tyrannosaurus 'Amargasaurus 'Deinonychus 'Compsognathus ' 'Count: 4 ' 'Contains("Deinonychus"): True ' 'readOnlyDinosaurs(3): Compsognathus ' 'IndexOf("Compsognathus"): 3 ' 'Insert into the wrapped List: 'Insert(2, "Oviraptor") ' 'Tyrannosaurus 'Amargasaurus 'Oviraptor 'Deinonychus 'Compsognathus ' 'Copied array has 7 elements: '"" '"Tyrannosaurus" '"Amargasaurus" '"Oviraptor" '"Deinonychus" '"Compsognathus" '""

#### .NET Framework

Supported in: 4.5.2, 4.5.1, 4.5, 4, 3.5, 3.0, 2.0#### .NET Framework Client Profile

Supported in: 4, 3.5 SP1#### Portable Class Library

Supported in: Portable Class Library#### .NET for Windows Store apps

Supported in: Windows 8#### .NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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

A ReadOnlyCollection(Of T) 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. To guarantee thread safety during enumeration, you can lock the collection during the entire enumeration. To allow the collection to be accessed by multiple threads for reading and writing, you must implement your own synchronization.