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

定義

指定したキーの値を取得または設定します。Gets or sets the value with the specified key.

property System::Object ^ System::Collections::IDictionary::Item[System::Object ^] { System::Object ^ get(System::Object ^ key); void set(System::Object ^ key, System::Object ^ value); };
object System.Collections.IDictionary.Item[object key] { get; set; }
 Property Item(key As Object) As Object Implements IDictionary.Item

パラメーター

key
Object Object Object

取得する値のキー。The key of the value to get.

プロパティ値

key がディクショナリにない場合、または keyDictionary<TKey,TValue> のキー型 TKey に代入できる型ではない場合は、指定したキーに関連付けられた値または nullThe value associated with the specified key, or null if key is not in the dictionary or key is of a type that is not assignable to the key type TKey of the Dictionary<TKey,TValue>.

実装

例外

値を代入しようとしていますが、key は、Dictionary<TKey,TValue> のキーの型 TKey に代入できない型です。A value is being assigned, and key is of a type that is not assignable to the key type TKey of the Dictionary<TKey,TValue>.

または-or- 値を代入しようとしていますが、value は、Dictionary<TKey,TValue> の値の型 TValue に代入できない型です。A value is being assigned, and value is of a type that is not assignable to the value type TValue of the Dictionary<TKey,TValue>.

次のコード例は、 IDictionary.Item[Object] System.Collections.IDictionaryインターフェイスのプロパティ (のインデクサー C#) をと共Dictionary<TKey,TValue>に使用する方法を示しています。また、 Dictionary<TKey,TValue>.Item[TKey]プロパティとプロパティの違いについて説明します。The following code example shows how to use the IDictionary.Item[Object] property (the indexer in C#) of the System.Collections.IDictionary interface with a Dictionary<TKey,TValue>, and ways the property differs from the Dictionary<TKey,TValue>.Item[TKey] property.

この例では、 Dictionary<TKey,TValue>.Item[TKey]プロパティDictionary<TKey,TValue>.IDictionary.Item[Object]と同様に、プロパティは既存のキーに関連付けられている値を変更でき、指定されたキーがディクショナリにない場合に新しいキーと値のペアを追加するために使用できます。The example shows that, like the Dictionary<TKey,TValue>.Item[TKey] property, the Dictionary<TKey,TValue>.IDictionary.Item[Object] property can change the value associated with an existing key and can be used to add a new key/value pair if the specified key is not in the dictionary. また、この例では、 Dictionary<TKey,TValue>.Item[TKey]プロパティDictionary<TKey,TValue>.IDictionary.Item[Object]とは異なり、がディクショナリに含まれkeyておらず、代わりに null 参照を返す場合に、プロパティが例外をスローしないことも示しています。The example also shows that unlike the Dictionary<TKey,TValue>.Item[TKey] property, the Dictionary<TKey,TValue>.IDictionary.Item[Object] property does not throw an exception if key is not in the dictionary, returning a null reference instead. 最後に、この例では、 Dictionary<TKey,TValue>.IDictionary.Item[Object]が正しいデータ型でないkey場合に、プロパティを取得すると null 参照が返されることを示しkeyています。また、が正しいデータ型でない場合は、プロパティを設定すると例外がスローされます。Finally, the example demonstrates that getting the Dictionary<TKey,TValue>.IDictionary.Item[Object] property returns a null reference if key is not the correct data type, and that setting the property throws an exception if key is not the correct data type.

このコード例は、 IDictionary.Addメソッドに指定された出力を含む、より大きな例の一部です。The code example is part of a larger example, including output, provided for the IDictionary.Add method.

using System;
using System.Collections;
using System.Collections.Generic;

public class Example
{
    public static void Main()
    {
        // Create a new dictionary of strings, with string keys,
        // and access it using the IDictionary interface.
        //
        IDictionary openWith = new Dictionary<string, string>();

        // Add some elements to the dictionary. There are no 
        // duplicate keys, but some of the values are duplicates.
        // IDictionary.Add throws an exception if incorrect types
        // are supplied for key or value.
        openWith.Add("txt", "notepad.exe");
        openWith.Add("bmp", "paint.exe");
        openWith.Add("dib", "paint.exe");
        openWith.Add("rtf", "wordpad.exe");
Imports System
Imports System.Collections
Imports System.Collections.Generic

Public Class Example
    
    Public Shared Sub Main() 

        ' Create a new dictionary of strings, with string keys,
        ' and access it using the IDictionary interface.
        '
        Dim openWith As IDictionary = _
            New Dictionary(Of String, String)
        
        ' Add some elements to the dictionary. There are no 
        ' duplicate keys, but some of the values are duplicates.
        ' IDictionary.Add throws an exception if incorrect types
        ' are supplied for key or value.
        openWith.Add("txt", "notepad.exe")
        openWith.Add("bmp", "paint.exe")
        openWith.Add("dib", "paint.exe")
        openWith.Add("rtf", "wordpad.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 indexer returns null if the key is of the wrong data 
// type.
Console.WriteLine("The indexer returns null" 
    + " if the key is of the wrong type:");
Console.WriteLine("For key = 2, value = {0}.", 
    openWith[2]);

// The indexer throws an exception when setting a value
// if the key is of the wrong data type.
try
{
    openWith[2] = "This does not get added.";
}
catch (ArgumentException)
{
    Console.WriteLine("A key of the wrong type was specified" 
        + " when assigning to the indexer.");
}
' 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 default Item property returns Nothing if the key
' is of the wrong data type.
Console.WriteLine("The default Item property returns Nothing" _
    & " if the key is of the wrong type:")
Console.WriteLine("For key = 2, value = {0}.", _
    openWith(2))

' The default Item property throws an exception when setting
' a value if the key is of the wrong data type.
Try
    openWith(2) = "This does not get added."
Catch 
    Console.WriteLine("A key of the wrong type was specified" _
        & " when setting the default Item property.")
End Try
// Unlike the default Item property on the Dictionary class
// itself, IDictionary.Item does not throw an exception
// if the requested key is not in the dictionary.
Console.WriteLine("For key = \"tif\", value = {0}.", 
    openWith["tif"]);
' Unlike the default Item property on the Dictionary class
' itself, IDictionary.Item does not throw an exception
' if the requested key is not in the dictionary.
Console.WriteLine("For key = ""tif"", value = {0}.", _
    openWith("tif"))
    }
}

    End Sub

End Class

注釈

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

また、 Item[Object]プロパティを使用して、ディクショナリに存在しないキーの値 (など) myCollection["myNonexistentKey"] = myValueを設定することによって、新しい要素を追加することもできます。You can also use the Item[Object] property to add new elements by setting the value of a key that does not exist in the dictionary; for example, myCollection["myNonexistentKey"] = myValue. ただし、指定したキーがディクショナリに既に存在する場合Item[Object]は、プロパティを設定すると古い値が上書きされます。However, if the specified key already exists in the dictionary, setting the Item[Object] property overwrites the old value. これに対してAdd 、メソッドは既存の要素を変更しません。In contrast, the Add method does not modify existing elements.

このC#言語ではIDictionary.Item[Object]プロパティを実装する代わりに、this キーワードを使用してインデクサーを定義します。The C# language uses the this keyword to define the indexers instead of implementing the IDictionary.Item[Object] property. Visual Basic は、IDictionary.Item[Object] 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 IDictionary.Item[Object] as a default property, which provides the same indexing functionality.

このプロパティの値を取得または設定すると、O (1) 操作に近づくことになります。Getting or setting the value of this property approaches an O(1) operation.

適用対象

こちらもご覧ください