Dictionary<TKey,TValue>.Item[TKey] Dictionary<TKey,TValue>.Item[TKey] Dictionary<TKey,TValue>.Item[TKey] Dictionary<TKey,TValue>.Item[TKey] Property

定義

指定されたキーに関連付けられている値を取得または設定します。Gets or sets the value associated with the specified key.

public:
 property TValue default[TKey] { TValue get(TKey key); void set(TKey key, TValue value); };
public TValue this[TKey key] { get; set; }
member this.Item('Key) : 'Value with get, set
Default Public Property Item(key As TKey) As TValue

パラメーター

key
TKey TKey TKey TKey

取得または設定する値のキー。The key of the value to get or set.

プロパティ値

TValue TValue TValue TValue

指定されたキーに関連付けられている値。The value associated with the specified key. 指定したキーが見つからなかった場合、get 操作は KeyNotFoundException をスローし、set 操作は指定したキーを持つ新しい要素を作成します。If the specified key is not found, a get operation throws a KeyNotFoundException, and a set operation creates a new element with the specified key.

実装

例外

プロパティが取得され、key がコレクションに存在しません。The property is retrieved and key does not exist in the collection.

次のコード例では、Item[TKey]プロパティ (c# のインデクサー) を示す値を取得する、KeyNotFoundException要求されたキーが存在しないと置き換えることができます、値がキーに関連付けられていることを示す場合にスローされます。The following code example uses the Item[TKey] property (the indexer in C#) to retrieve values, demonstrating that a KeyNotFoundException is thrown when a requested key is not present, and showing that the value associated with a key can be replaced.

使用する方法も示します、TryGetValue場合は、プログラムは多くの場合、ディクショナリではありません。 キーの値を試みる必要があります値を取得するより効率的な方法としてのメソッド。The example also shows how to use the TryGetValue method as a more efficient way to retrieve values if a program often must try key values that are not in the dictionary.

このコード例が示されている例の一部、Dictionary<TKey,TValue>クラス。This code example is part of a larger example provided for the Dictionary<TKey,TValue> class. openWith この例で使用されるディクショナリの名前です。openWith is the name of the Dictionary used in this example.

// Create a new dictionary of strings, with string keys.
//
Dictionary<String^, String^>^ openWith =
    gcnew Dictionary<String^, String^>();

// Add some elements to the dictionary. There are no
// duplicate keys, but some of the values are duplicates.
openWith->Add("txt", "notepad.exe");
openWith->Add("bmp", "paint.exe");
openWith->Add("dib", "paint.exe");
openWith->Add("rtf", "wordpad.exe");

// The Add method throws an exception if the new key is
// already in the dictionary.
try
{
    openWith->Add("txt", "winword.exe");
}
catch (ArgumentException^)
{
    Console::WriteLine("An element with Key = \"txt\" already exists.");
}
// Create a new dictionary of strings, with string keys.
//
Dictionary<string, string> openWith = 
    new Dictionary<string, string>();

// Add some elements to the dictionary. There are no 
// duplicate keys, but some of the values are duplicates.
openWith.Add("txt", "notepad.exe");
openWith.Add("bmp", "paint.exe");
openWith.Add("dib", "paint.exe");
openWith.Add("rtf", "wordpad.exe");

// The Add method throws an exception if the new key is 
// already in the dictionary.
try
{
    openWith.Add("txt", "winword.exe");
}
catch (ArgumentException)
{
    Console.WriteLine("An element with Key = \"txt\" already exists.");
}
' Create a new dictionary of strings, with string keys.
'
Dim openWith As New Dictionary(Of String, String)

' Add some elements to the dictionary. There are no 
' duplicate keys, but some of the values are duplicates.
openWith.Add("txt", "notepad.exe")
openWith.Add("bmp", "paint.exe")
openWith.Add("dib", "paint.exe")
openWith.Add("rtf", "wordpad.exe")

' The Add method throws an exception if the new key is 
' already in the dictionary.
Try
    openWith.Add("txt", "winword.exe")
Catch 
    Console.WriteLine("An element with Key = ""txt"" already exists.")
End Try
// The Item property is another name for the indexer, so you
// can omit its name when accessing elements.
Console::WriteLine("For key = \"rtf\", value = {0}.",
    openWith["rtf"]);

// The indexer can be used to change the value associated
// with a key.
openWith["rtf"] = "winword.exe";
Console::WriteLine("For key = \"rtf\", value = {0}.",
    openWith["rtf"]);

// If a key does not exist, setting the indexer for that key
// adds a new key/value pair.
openWith["doc"] = "winword.exe";
// The Item property is another name for the indexer, so you 
// can omit its name when accessing elements. 
Console.WriteLine("For key = \"rtf\", value = {0}.", 
    openWith["rtf"]);

// The indexer can be used to change the value associated
// with a key.
openWith["rtf"] = "winword.exe";
Console.WriteLine("For key = \"rtf\", value = {0}.", 
    openWith["rtf"]);

// If a key does not exist, setting the indexer for that key
// adds a new key/value pair.
openWith["doc"] = "winword.exe";
' The Item property is the default property, so you 
' can omit its name when accessing elements. 
Console.WriteLine("For key = ""rtf"", value = {0}.", _
    openWith("rtf"))

' The default Item property can be used to change the value
' associated with a key.
openWith("rtf") = "winword.exe"
Console.WriteLine("For key = ""rtf"", value = {0}.", _
    openWith("rtf"))

' If a key does not exist, setting the default Item property
' for that key adds a new key/value pair.
openWith("doc") = "winword.exe"
// 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
// 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

注釈

このプロパティは、次の c# の構文を使用して、コレクション内の特定の要素にアクセスする機能を提供します。 myCollection[key] (myCollection(key) Visual Basic で)。This property provides the ability to access a specific element in the collection by using the following C# syntax: myCollection[key] (myCollection(key) in Visual Basic).

使用することも、Item[TKey]にキーの値を設定して、新しい要素を追加するプロパティが存在しません、Dictionary<TKey,TValue>します。You can also use the Item[TKey] property to add new elements by setting the value of a key that does not exist in the Dictionary<TKey,TValue>. キーがである場合に、プロパティの値を設定すると、 Dictionary<TKey,TValue>、そのキーに関連付けられている値が割り当てられている値に置き換えします。When you set the property value, if the key is in the Dictionary<TKey,TValue>, the value associated with that key is replaced by the assigned value. キーがない場合、Dictionary<TKey,TValue>キーと値がディクショナリに追加します。If the key is not in the Dictionary<TKey,TValue>, the key and value are added to the dictionary. これに対し、Addメソッドでは、既存の要素は変更しません。In contrast, the Add method does not modify existing elements.

キーにはnull、ですが、値を入力する場合の値がTValueは参照型です。A key cannot be null, but a value can be, if the value type TValue is a reference type.

C#使用する言語、 this キーワードを実装する代わりに、インデクサーの定義、Item[TKey]プロパティ。The C# language uses the this keyword to define the indexers instead of implementing the Item[TKey] property. Visual Basic は、Item[TKey] を既定のプロパティとして実装しており、同様のインデックス機能を提供します。Visual Basic implements Item[TKey] as a default property, which provides the same indexing functionality.

このプロパティの値の設定を取得または o (1) 操作に近くなります。Getting or setting the value of this property approaches an O(1) operation.

適用対象

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