IDictionary Interface
Represents a nongeneric collection of key/value pairs.
Assembly: mscorlib (in mscorlib.dll)
The IDictionary type exposes the following members.
| Name | Description | |
|---|---|---|
![]() ![]() | Count | Gets the number of elements contained in the ICollection. (Inherited from ICollection.) |
![]() ![]() | IsFixedSize | Gets a value indicating whether the IDictionary object has a fixed size. |
![]() ![]() | IsReadOnly | Gets a value indicating whether the IDictionary object is read-only. |
![]() ![]() | IsSynchronized | Gets a value indicating whether access to the ICollection is synchronized (thread safe). (Inherited from ICollection.) |
![]() ![]() | Item | Gets or sets the element with the specified key. |
![]() ![]() | Keys | Gets an ICollection object containing the keys of the IDictionary object. |
![]() ![]() | SyncRoot | Gets an object that can be used to synchronize access to the ICollection. (Inherited from ICollection.) |
![]() ![]() | Values | Gets an ICollection object containing the values in the IDictionary object. |
| Name | Description | |
|---|---|---|
![]() ![]() | Add | Adds an element with the provided key and value to the IDictionary object. |
![]() ![]() | Clear | Removes all elements from the IDictionary object. |
![]() ![]() | Contains | Determines whether the IDictionary object contains an element with the specified key. |
![]() ![]() | CopyTo | Copies the elements of the ICollection to an Array, starting at a particular Array index. (Inherited from ICollection.) |
![]() ![]() | GetEnumerator | Returns an IDictionaryEnumerator object for the IDictionary object. |
![]() ![]() | Remove | Removes the element with the specified key from the IDictionary object. |
| Name | Description | |
|---|---|---|
![]() | AsParallel | Enables parallelization of a query. (Defined by ParallelEnumerable.) |
![]() | AsQueryable | Converts an IEnumerable to an IQueryable. (Defined by Queryable.) |
![]() ![]() | Cast<TResult> | Casts the elements of an IEnumerable to the specified type. (Defined by Enumerable.) |
![]() ![]() | OfType<TResult> | Filters the elements of an IEnumerable based on a specified type. (Defined by Enumerable.) |
The IDictionary interface is the base interface for nongeneric collections of key/value pairs. For the generic version of this interface, see System.Collections.Generic::IDictionary<TKey, TValue>.
Each element is a key/value pair stored in a DictionaryEntry object.
Each pair must have a unique key. Implementations can vary in whether they allow the key to be null. The value can be null and does not have to be unique. The IDictionary interface allows the contained keys and values to be enumerated, but it does not imply any particular sort order.
IDictionary implementations fall into three categories: read-only, fixed-size, variable-size. A read-only IDictionary object cannot be modified. A fixed-size IDictionary object does not allow the addition or removal of elements, but does allow the modification of existing elements. A variable-size IDictionary object allows the addition, removal, and modification of elements.
The foreach statement of the C# language (For Each in Visual Basic) requires the type of each element in the collection. Since each element of the IDictionary object is a key/value pair, the element type is not the type of the key or the type of the value. Instead, the element type is DictionaryEntry. For example:
The foreach statement is a wrapper around the enumerator, which allows only reading from but not writing to the collection.
Notes to ImplementersThe implementing class must have a means to compare keys.
The following code example demonstrates how to define a simple dictionary class that implements the IDictionary interface.
using namespace System; using namespace System::Collections; // This class implements a simple dictionary using an array of // DictionaryEntry objects (key/value pairs). public ref class SimpleDictionary : public IDictionary { // The array of items private: array<DictionaryEntry^>^ items; private: int itemsInUse; // Construct the SimpleDictionary with the desired number of // items. The number of items cannot change for the life time of // this SimpleDictionary. public: SimpleDictionary(int size) { items = gcnew array<DictionaryEntry^>(size); } #pragma region IDictionary Members public: property virtual bool IsReadOnly { bool get() { return false; } } public: virtual bool Contains(Object^ key) { int index; return TryGetIndexOfKey(key, &index); } public: virtual property bool IsFixedSize { bool get() { return false; } } public: virtual void Remove(Object^ key) { if (key == nullptr) { throw gcnew ArgumentNullException("key"); } // Try to find the key in the DictionaryEntry array int index; if (TryGetIndexOfKey(key, &index)) { // If the key is found, slide all the items down. Array::Copy(items, index + 1, items, index, itemsInUse - index - 1); itemsInUse--; } else { // If the key is not in the dictionary, just return. return; } } public: virtual void Clear() { itemsInUse = 0; } public: virtual void Add(Object^ key, Object^ value) { // Add the new key/value pair even if this key already exists // in the dictionary. if (itemsInUse == items->Length) { throw gcnew InvalidOperationException ("The dictionary cannot hold any more items."); } items[itemsInUse++] = gcnew DictionaryEntry(key, value); } public: virtual property ICollection^ Keys { ICollection^ get() { // Return an array where each item is a key. array<Object^>^ keys = gcnew array<Object^>(itemsInUse); for (int i = 0; i < itemsInUse; i++) { keys[i] = items[i]->Key; } return keys; } } public: virtual property ICollection^ Values { ICollection^ get() { // Return an array where each item is a value. array<Object^>^ values = gcnew array<Object^>(itemsInUse); for (int i = 0; i < itemsInUse; i++) { values[i] = items[i]->Value; } return values; } } public: virtual property Object^ default[Object^] { Object^ get(Object^ key) { // If this key is in the dictionary, return its value. int index; if (TryGetIndexOfKey(key, &index)) { // The key was found; return its value. return items[index]->Value; } else { // The key was not found; return null. return nullptr; } } void set(Object^ key, Object^ value) { // If this key is in the dictionary, change its value. int index; if (TryGetIndexOfKey(key, &index)) { // The key was found; change its value. items[index]->Value = value; } else { // This key is not in the dictionary; add this // key/value pair. Add(key, value); } } } private: bool TryGetIndexOfKey(Object^ key, int* index) { for (*index = 0; *index < itemsInUse; *index++) { // If the key is found, return true (the index is also // returned). if (items[*index]->Key->Equals(key)) { return true; } } // Key not found, return false (index should be ignored by // the caller). return false; } private: ref class SimpleDictionaryEnumerator : public IDictionaryEnumerator { // A copy of the SimpleDictionary object's key/value pairs. private: array<DictionaryEntry^>^ items; private: int index; public: SimpleDictionaryEnumerator(SimpleDictionary^ sd) { // Make a copy of the dictionary entries currently in the // SimpleDictionary object. items = gcnew array<DictionaryEntry^>(sd->Count); Array::Copy(sd->items, 0, items, 0, sd->Count); index = -1; } // Return the current item. public: virtual property Object^ Current { Object^ get() { ValidateIndex(); return items[index]; } } // Return the current dictionary entry. public: virtual property DictionaryEntry Entry { DictionaryEntry get() { return (DictionaryEntry) Current; } } // Return the key of the current item. public: virtual property Object^ Key { Object^ get() { ValidateIndex(); return items[index]->Key; } } // Return the value of the current item. public: virtual property Object^ Value { Object^ get() { ValidateIndex(); return items[index]->Value; } } // Advance to the next item. public: virtual bool MoveNext() { if (index < items->Length - 1) { index++; return true; } return false; } // Validate the enumeration index and throw an exception if // the index is out of range. private: void ValidateIndex() { if (index < 0 || index >= items->Length) { throw gcnew InvalidOperationException ("Enumerator is before or after the collection."); } } // Reset the index to restart the enumeration. public: virtual void Reset() { index = -1; } }; public: virtual IDictionaryEnumerator^ GetEnumerator() { // Construct and return an enumerator. return gcnew SimpleDictionaryEnumerator(this); } #pragma endregion #pragma region ICollection Members public: virtual property bool IsSynchronized { bool get() { return false; } } public: virtual property Object^ SyncRoot { Object^ get() { throw gcnew NotImplementedException(); } } public: virtual property int Count { int get() { return itemsInUse; } } public: virtual void CopyTo(Array^ array, int index) { throw gcnew NotImplementedException(); } #pragma endregion #pragma region IEnumerable Members virtual IEnumerator^ IEnumerable_GetEnumerator() = IEnumerable::GetEnumerator { // Construct and return an enumerator. return ((IDictionary^)this)->GetEnumerator(); } #pragma endregion }; int main() { // Create a dictionary that contains no more than three // entries. IDictionary^ d = gcnew SimpleDictionary(3); // Add three people and their ages to the dictionary. d->Add("Jeff", 40); d->Add("Kristin", 34); d->Add("Aidan", 1); Console::WriteLine("Number of elements in dictionary = {0}", d->Count); Console::WriteLine("Does dictionary contain 'Jeff'? {0}", d->Contains("Jeff")); Console::WriteLine("Jeff's age is {0}", d["Jeff"]); // Display every entry's key and value. for each (DictionaryEntry^ de in d) { Console::WriteLine("{0} is {1} years old.", de->Key, de->Value); } // Remove an entry that exists. d->Remove("Jeff"); // Remove an entry that does not exist, but do not throw an // exception. d->Remove("Max"); // Show the names (keys) of the people in the dictionary. for each (String^ s in d->Keys) { Console::WriteLine(s); } // Show the ages (values) of the people in the dictionary. for each (int age in d->Values) { Console::WriteLine(age); } } // This code produces the following output. // // Number of elements in dictionary = 3 // Does dictionary contain 'Jeff'? True // Jeff's age is 40 // Jeff is 40 years old. // Kristin is 34 years old. // Aidan is 1 years old. // Kristin // Aidan // 34 // 1
Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
