IDictionary.TryGetValue Method
Assembly: mscorlib (in mscorlib.dll)
'Declaration Function TryGetValue ( _ key As TKey, _ <OutAttribute> ByRef value As TValue _ ) As Boolean 'Usage Dim instance As IDictionary(Of TKey, TValue) Dim key As TKey Dim value As TValue Dim returnValue As Boolean returnValue = instance.TryGetValue(key, value)
boolean TryGetValue ( TKey key, /** @attribute OutAttribute() */ /** @ref */ TValue value )
Not applicable.
Parameters
- key
The key whose value to get.
- value
When this method returns, 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
true if the object that implements IDictionary contains an element with the specified key; otherwise, false.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 value type V; for example, zero (0) for integer types, false for Boolean types, and a null reference (Nothing in Visual Basic) for reference types.
The example shows how to use the TryGetValue method to retrieve values. If a program frequently tries key values that are not in a dictionary, the TryGetValue method can be more efficient than using the Item property (the indexer in C#), which throws exceptions when attempting to retrieve nonexistent keys.
This code is part of a larger example that can be compiled and executed. See System.Collections.Generic.IDictionary.
' 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
Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.