IDictionary(Of TKey, TValue).TryGetValue Method
Gets the value associated with the specified key.
Namespace: System.Collections.Generic
Assembly: mscorlib (in mscorlib.dll)
'Declaration Function TryGetValue ( _ key As TKey, _ <OutAttribute> ByRef value As TValue _ ) As Boolean
Parameters
- key
- Type: TKey
The key whose value to get.
- value
- Type: TValue%
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
Type: System.Booleantrue if the object that implements IDictionary(Of TKey, TValue) contains an element with the specified key; otherwise, false.
| Exception | Condition |
|---|---|
| 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 value type V; for example, zero (0) for integer types, false for Boolean types, and Nothing 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(Of TKey, TValue).
' 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 outputBlock.Text &= String.Format("For key = ""tif"", value = {0}.", value) & vbCrLf Else outputBlock.Text &= "Key = ""tif"" is not found." & vbCrLf End If ... ' The default Item property throws an exception if the requested ' key is not in the dictionary. Try outputBlock.Text &= String.Format("For key = ""tif"", value = {0}.", _ openWith("tif")) & vbCrLf Catch outputBlock.Text &= "Key = ""tif"" is not found." & vbCrLf End Try
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