Dictionary<TKey, TValue>.TryGetValue Method
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Gets the value associated with the specified key.
Namespace: System.Collections.Generic
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
Public Function TryGetValue ( _
key As TKey, _
<OutAttribute> ByRef value As TValue _
) As Boolean
public bool TryGetValue(
TKey key,
out TValue value
)
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<TKey, TValue> contains an element with the specified key; otherwise, false.
Implements
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | key is nulla null reference (Nothing in Visual Basic). |
Remarks
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 TValue; for example, 0 (zero) for integer types, false for Boolean types, and nulla null reference (Nothing in Visual Basic) 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.
Examples
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<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
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
// 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.
string value = "";
if (openWith.TryGetValue("tif", out value))
{
outputBlock.Text += String.Format("For key = \"tif\", value = {0}.", value) + "\n";
}
else
{
outputBlock.Text += "Key = \"tif\" is not found." + "\n";
}
...
// The indexer throws an exception if the requested key is
// not in the dictionary.
try
{
outputBlock.Text += String.Format("For key = \"tif\", value = {0}.",
openWith["tif"]) + "\n";
}
catch (KeyNotFoundException)
{
outputBlock.Text += "Key = \"tif\" is not found." + "\n";
}
Version Information
Silverlight
Supported in: 5, 4, 3
Silverlight for Windows Phone
Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0
XNA Framework
Supported in: Xbox 360, Windows Phone OS 7.0
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.
See Also