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

定義

指定したキーが Dictionary<TKey,TValue> に格納されているかどうかを判断します。 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
パラメーター
key
TKey TKey TKey TKey

Dictionary<TKey,TValue> 内で検索されるキー。 The key to locate in the Dictionary<TKey,TValue>.

戻り値

指定したキーを持つ要素が true に格納されている場合は Dictionary<TKey,TValue>。それ以外の場合は false true if the Dictionary<TKey,TValue> contains an element with the specified key; otherwise, false.

実装
例外

次のコード例を使用する方法を示しています、ContainsKeyメソッドを呼び出す前に、キーが存在するかどうかをテストする、Addメソッド。The following code example shows how to use the ContainsKey method to test whether a key exists prior to calling the Add method. 使用する方法も示します、TryGetValueプログラムは、ディクショナリにないキーを頻繁に試行するときに、値を取得する、効率的な方法は、値を取得するメソッド。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. 最後に、表示をテストする最も非効率的な方法では、Item[TKey]プロパティ (c# のインデクサー)。Finally, it shows the least efficient way to test whether keys exist, by using the Item[TKey] property (the indexer in C#).

このコード例が示されている例の一部、Dictionary<TKey,TValue>クラス (openWithはこの例で使用されるディクショナリの名前です)。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

注釈

このメソッドは、o (1) 操作に近くなります。This method approaches an O(1) operation.

適用対象

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