IDictionary::Item Property (Object^)


Gets or sets the element with the specified key.

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

property Object^ default[
	Object^ key
] {
	Object^ get(Object^ key);
	void set(Object^ key, Object^ value);


Type: System::Object^

The key of the element to get or set.

Property Value

Type: System::Object^

The element with the specified key, or null if the key does not exist.

Exception Condition

key is null.


The property is set and the IDictionary object is read-only.


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 null.

The C# language uses the thisthis (C# Reference) 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.

    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;
                // 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;
                // This key is not in the dictionary; add this
                // key/value pair.
                Add(key, value);

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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