Dictionary(Of TKey, TValue).TryGetValue Method

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

Implements

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

.NET Framework Client Profile

Portable Class Library

.NET for Windows Store apps

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.

Reference