IDictionary<TKey,TValue>.TryGetValue(TKey, TValue) Method

Reference

Definition

Namespace:: System.Collections.Generic

Assembly:: System.Runtime.dll

Assembly:: mscorlib.dll

Assembly:: netstandard.dll

Important

Some information relates to prerelease product that may be substantially modified before it’s released. Microsoft makes no warranties, express or implied, with respect to the information provided here.

Gets the value associated with the specified key.

public:
 bool TryGetValue(TKey key, [Runtime::InteropServices::Out] TValue % value);

public bool TryGetValue (TKey key, out TValue value);

abstract member TryGetValue : 'Key * 'Value -> bool

Public Function TryGetValue (key As TKey, ByRef value As TValue) As Boolean

Parameters

key: TKey

The key whose value to get.

value: 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.

Returns

Boolean

true if the object that implements IDictionary<TKey,TValue> contains an element with the specified key; otherwise, false.

Exceptions

ArgumentNullException

key is null.

Examples

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<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.
String^ value = "";
if (openWith->TryGetValue("tif", value))
{
    Console::WriteLine("For key = \"tif\", value = {0}.", value);
}
else
{
    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", out value))
{
    Console.WriteLine("For key = \"tif\", value = {0}.", value);
}
else
{
    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.
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 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.");
}

// 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.");
}

' 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

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 type TValue; for example, zero (0) for integer types, false for Boolean types, and null for reference types.

Applies to

Deila með