Dictionary<TKey,TValue>.ContainsKey(TKey) Method

Definition

Bestimmt, ob das Dictionary<TKey,TValue> den angegebenen Schlüssel enthält.Determines whether the Dictionary<TKey,TValue> contains the specified key.

public:
 virtual bool ContainsKey(TKey key);
public bool ContainsKey (TKey key);
abstract member ContainsKey : 'Key -> bool
override this.ContainsKey : 'Key -> bool
Public Function ContainsKey (key As TKey) As Boolean

Parameters

key
TKey

Der Schlüssel, der in der Dictionary<TKey,TValue> gesucht werden soll.The key to locate in the Dictionary<TKey,TValue>.

Returns

Boolean

true, wenn die Dictionary<TKey,TValue> ein Element mit dem angegebenen Schlüssel enthält; andernfalls false.true if the Dictionary<TKey,TValue> contains an element with the specified key; otherwise, false.

Implements

Exceptions

key ist nullkey is null.

Examples

Im folgenden Codebeispiel wird gezeigt, wie die ContainsKey-Methode verwendet wird, um zu testen, ob ein Schlüssel vorhanden ist, bevor die Add-Methode aufgerufen wird.The following code example shows how to use the ContainsKey method to test whether a key exists prior to calling the Add method. Außerdem wird gezeigt, wie die TryGetValue-Methode zum Abrufen von Werten verwendet wird. Dies ist eine effiziente Methode zum Abrufen von Werten, wenn ein Programm häufig Schlüssel verwendet, die nicht im Wörterbuch vorhanden sind.It also shows how to use the TryGetValue method to retrieve values, which is an efficient way to retrieve values when a program frequently tries keys that are not in the dictionary. Zum Schluss zeigt es die geringste effiziente Methode, um zu testen, ob Schlüssel vorhanden sind, indem die Item[]-Eigenschaft ( C#der Indexer in) verwendet wird.Finally, it shows the least efficient way to test whether keys exist, by using the Item[] property (the indexer in C#).

Dieses Codebeispiel ist Teil eines größeren Beispiels, das für die Dictionary<TKey,TValue>-Klasse bereitgestellt wird (openWith ist der Name des Wörterbuchs, das in diesem Beispiel verwendet wird).This code example is part of a larger example provided for the Dictionary<TKey,TValue> class (openWith is the name of the Dictionary used in this example).

// ContainsKey can be used to test keys before inserting
// them.
if (!openWith->ContainsKey("ht"))
{
    openWith->Add("ht", "hypertrm.exe");
    Console::WriteLine("Value added for key = \"ht\": {0}",
        openWith["ht"]);
}
// ContainsKey can be used to test keys before inserting
// them.
if (!openWith.ContainsKey("ht"))
{
    openWith.Add("ht", "hypertrm.exe");
    Console.WriteLine("Value added for key = \"ht\": {0}",
        openWith["ht"]);
}
' ContainsKey can be used to test keys before inserting 
' them.
If Not openWith.ContainsKey("ht") Then
    openWith.Add("ht", "hypertrm.exe")
    Console.WriteLine("Value added for key = ""ht"": {0}", _
        openWith("ht"))
End If
// 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

Diese Methode nähert sich einem O (1)-Vorgang.This method approaches an O(1) operation.

Applies to

See also