ConcurrentDictionary(Of TKey, TValue).TryUpdate Method (TKey, TValue, TValue)

.NET Framework (current version)
 
System_CAPS_noteNote

The .NET API Reference documentation has a new home. Visit the .NET API Browser on docs.microsoft.com to see the new experience.

Compares the existing value for the specified key with a specified value, and if they are equal, updates the key with a third value.

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

Public Function TryUpdate (
	key As TKey,
	newValue As TValue,
	comparisonValue As TValue
) As Boolean

Parameters

key
Type: TKey

The key whose value is compared with comparisonValue and possibly replaced.

newValue
Type: TValue

The value that replaces the value of the element that has the specified key if the comparison results in equality.

comparisonValue
Type: TValue

The value that is compared to the value of the element that has the specified key.

Return Value

Type: System.Boolean

true if the value with key was equal to comparisonValue and was replaced with newValue; otherwise, false.

Exception Condition
ArgumentNullException

key is null.

The following example shows how to call the TryUpdate method:

'Imports System.Collections.Concurrent

Class CD_TryXYZ

    ' Demonstrates:
    ' ConcurrentDictionary<TKey, TValue>.TryAdd()
    ' ConcurrentDictionary<TKey, TValue>.TryUpdate()
    ' ConcurrentDictionary<TKey, TValue>.TryRemove()
    Shared Sub Main()
        Dim numFailures As Integer = 0
        ' for bookkeeping
        ' Construct an empty dictionary
        Dim cd As ConcurrentDictionary(Of Integer, [String]) = New ConcurrentDictionary(Of Integer, String)()

        ' This should work
        If Not cd.TryAdd(1, "one") Then
            Console.WriteLine("CD.TryAdd() failed when it should have succeeded")
            numFailures += 1
        End If

        ' This shouldn't work -- key 1 is already in use
        If cd.TryAdd(1, "uno") Then
            Console.WriteLine("CD.TryAdd() succeeded when it should have failed")
            numFailures += 1
        End If

        ' Now change the value for key 1 from "one" to "uno" -- should work
        If Not cd.TryUpdate(1, "uno", "one") Then
            Console.WriteLine("CD.TryUpdate() failed when it should have succeeded")
            numFailures += 1
        End If

        ' Try to change the value for key 1 from "eine" to "one" 
        ' -- this shouldn't work, because the current value isn't "eine"
        If cd.TryUpdate(1, "one", "eine") Then
            Console.WriteLine("CD.TryUpdate() succeeded when it should have failed")
            numFailures += 1
        End If

        ' Remove key/value for key 1. Should work.
        Dim value1 As String = ""
        If Not cd.TryRemove(1, value1) Then
            Console.WriteLine("CD.TryRemove() failed when it should have succeeded")
            numFailures += 1
        End If

        ' Remove key/value for key 1. Shouldn't work, because I already removed it
        Dim value2 As String = ""
        If cd.TryRemove(1, value2) Then
            Console.WriteLine("CD.TryRemove() succeeded when it should have failed")
            numFailures += 1
        End If

        ' If nothing went wrong, say so
        If numFailures = 0 Then
            Console.WriteLine(" OK!")
        End If
    End Sub
End Class

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone
Available since 8.1
Return to top
Show: