Export (0) Print
Expand All

Dictionary(Of TKey, TValue).TryGetValue Method

Gets the value associated with the specified key.

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

'Declaration
Public Function TryGetValue ( _
	key As TKey, _
	<OutAttribute> ByRef value As TValue _
) As Boolean

Parameters

key
Type: TKey

The key of the value to get.

value
Type: TValue

When this method returns, contains the value associated with the specified key, if the key is found; otherwise, the default value for the type of the value parameter. This parameter is passed uninitialized.

Return Value

Type: System.Boolean
true if the Dictionary(Of TKey, TValue) contains an element with the specified key; otherwise, false.

Implements

IDictionary(Of TKey, TValue).TryGetValue(TKey, TValue)
IReadOnlyDictionary(Of TKey, TValue).TryGetValue(TKey, TValue)

ExceptionCondition
ArgumentNullException

key is Nothing.

This method combines the functionality of the ContainsKey method and the Item property.

If the key is not found, then the value parameter gets the appropriate default value for the type TValue; for example, 0 (zero) for integer types, false for Boolean types, and Nothing for reference types.

Use the TryGetValue method if your code frequently attempts to access keys that are not in the dictionary. Using this method is more efficient than catching the KeyNotFoundException thrown by the Item property.

This method approaches an O(1) operation.

The example shows how to use the TryGetValue method as a more efficient way to retrieve values in a program that frequently tries keys that are not in the dictionary. For contrast, the example also shows how the Item property (the indexer in C#) throws exceptions when attempting to retrieve nonexistent keys.

This code example is part of a larger example provided for the Dictionary(Of TKey, TValue) class.

' When a program often has to try keys that turn out not to 
' be in the dictionary, TryGetValue can be a more efficient  
' way to retrieve values. 
Dim value As String = "" 
If openWith.TryGetValue("tif", value) Then
    Console.WriteLine("For key = ""tif"", value = {0}.", value)
Else
    Console.WriteLine("Key = ""tif"" is not found.")
End If


...


' The default Item property throws an exception if the requested 
' key is not in the dictionary. 
Try
    Console.WriteLine("For key = ""tif"", value = {0}.", _
        openWith("tif"))
Catch 
    Console.WriteLine("Key = ""tif"" is not found.")
End Try

.NET Framework

Supported in: 4.5, 4, 3.5, 3.0, 2.0

.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

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone Silverlight 8.1, 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.

Show:
© 2014 Microsoft