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IDictionary.Add Method

Adds an element with the provided key and value to the IDictionary object.

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

void Add(
	Object key,
	Object value
)

Parameters

key
Type: System.Object

The Object to use as the key of the element to add.

value
Type: System.Object

The Object to use as the value of the element to add.

ExceptionCondition
ArgumentNullException

key is null.

ArgumentException

An element with the same key already exists in the IDictionary object.

NotSupportedException

The IDictionary is read-only.

-or-

The IDictionary has a fixed size.

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 following code example demonstrates how to implement the Add method. This code example is part of a larger example provided for the IDictionary class.

public 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 new InvalidOperationException("The dictionary cannot hold any more items.");
    items[ItemsInUse++] = new DictionaryEntry(key, value);
}

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.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

Supported in: Windows Phone 8.1

Supported in: Windows Phone Silverlight 8.1

Supported in: Windows Phone Silverlight 8

Windows 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.

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