Gets the value associated with the specified key.
Assembly: mscorlib (in mscorlib.dll)
Public Function TryGetValue ( _
key As TKey, _
<[%$TOPIC/bb347013_en-us_VS_110_1_0_0_0_0%]> ByRef value As TValue _
) As [%$TOPIC/bb347013_en-us_VS_110_1_0_0_0_1%]public [%$TOPIC/bb347013_en-us_VS_110_1_0_1_0_0%] TryGetValue(
TKey key,
out TValue value
)public:
virtual [%$TOPIC/bb347013_en-us_VS_110_1_0_2_0_0%] TryGetValue(
TKey key,
[[%$TOPIC/bb347013_en-us_VS_110_1_0_2_0_1%]] TValue% value
) sealedabstract TryGetValue :
key:'TKey *
value:'TValue byref -> [%$TOPIC/bb347013_en-us_VS_110_1_0_3_0_0%]
override TryGetValue :
key:'TKey *
value:'TValue byref -> [%$TOPIC/bb347013_en-us_VS_110_1_0_3_0_1%]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: SystemBooleantrue if the DictionaryTKey, TValue contains an element with the specified key; otherwise, false.
Implements
IDictionaryTKey, TValueTryGetValue(TKey, TValue)IReadOnlyDictionaryTKey, TValueTryGetValue(TKey, TValue)
| Exception | Condition |
|---|---|
| ArgumentNullException | key is . |
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 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 DictionaryTKey, 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// 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))
{
Console.WriteLine("For key = \"tif\", value = {0}.", value);
}
else
{
Console.WriteLine("Key = \"tif\" is not found.");
}
...
// The indexer throws an exception if the requested key is
// not in the dictionary.
try
{
Console.WriteLine("For key = \"tif\", value = {0}.",
openWith["tif"]);
}
catch (KeyNotFoundException)
{
Console.WriteLine("Key = \"tif\" is not found.");
}// 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", value))
{
Console::WriteLine("For key = \"tif\", value = {0}.", value);
}
else
{
Console::WriteLine("Key = \"tif\" is not found.");
}
...
// The indexer throws an exception if the requested key is
// not in the dictionary.
try
{
Console::WriteLine("For key = \"tif\", value = {0}.",
openWith["tif"]);
}
catch (KeyNotFoundException^)
{
Console::WriteLine("Key = \"tif\" is not found.");
}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.
