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ConcurrentDictionary<TKey, TValue>.AddOrUpdate Method (TKey, TValue, Func<TKey, TValue, TValue>)

Adds a key/value pair to the ConcurrentDictionary<TKey, TValue> if the key does not already exist, or uses the specified function to update a key/value pair in the ConcurrentDictionary<TKey, TValue> if the key already exists.

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

public TValue AddOrUpdate(
	TKey key,
	TValue addValue,
	Func<TKey, TValue, TValue> updateValueFactory


Type: TKey
The key to be added or whose value should be updated
Type: TValue
The value to be added for an absent key
Type: System.Func<TKey, TValue, TValue>
The function used to generate a new value for an existing key based on the key's existing value

Return Value

Type: TValue
The new value for the key. This will be either be addValue (if the key was absent) or the result of updateValueFactory (if the key was present).


key is a null reference (Nothing in Visual Basic).


updateValueFactory is a null reference (Nothing in Visual Basic).


The dictionary already contains the maximum number of elements, MaxValue.

.NET Framework

Supported in: 4

.NET Framework Client Profile

Supported in: 4

Windows 7, Windows Vista SP1 or later, Windows XP SP3, 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.