IDictionary::Item Property
Gets or sets the element with the specified key.
Assembly: mscorlib (in mscorlib.dll)
property Object^ Item[Object^ key] { Object^ get (Object^ key); void set (Object^ key, Object^ value); }
Parameters
- key
- Type: System::Object
The key of the element to get or set.
| Exception | Condition |
|---|---|
| ArgumentNullException | key is nullptr. |
| NotSupportedException | The property is set and the IDictionary object is read-only. -or- The property is set, key does not exist in the collection, and the IDictionary has a fixed size. |
This property provides the ability to access a specific element in the collection by using the following syntax: myCollection[key].
You can also use the Item property to add new elements by setting the value of a key that does not exist in the dictionary (for example, myCollection["myNonexistentKey"] = myValue). However, if the specified key already exists in the dictionary, setting the Item property overwrites the old value. In contrast, the Add method does not modify existing elements.
Implementations can vary in whether they allow the key to be nullptr.
The C# language uses the this keyword to define the indexers instead of implementing the Item property. Visual Basic implements Item as a default property, which provides the same indexing functionality.
The following code example demonstrates how to implement the Item property. This code example is part of a larger example provided for the IDictionary class.
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); } } }
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.