HybridDictionary.Item[Object] 屬性
定義
重要
部分資訊涉及發行前產品，在發行之前可能會有大幅修改。 Microsoft 對此處提供的資訊，不做任何明確或隱含的瑕疵擔保。
取得或設定與指定之索引鍵相關聯的值。
public:
property System::Object ^ default[System::Object ^] { System::Object ^ get(System::Object ^ key); void set(System::Object ^ key, System::Object ^ value); };public object this[object key] { get; set; }public object? this[object key] { get; set; }member this.Item(obj) : obj with get, setDefault Public Property Item(key As Object) As Object參數
- key
- Object
索引鍵，要讀取或設定其值。
屬性值
與指定之索引鍵關聯的值。 如果找不到指定的索引鍵，嘗試取得它將傳回 null，而嘗試設定它將以指定的索引鍵建立新的項目。
實作
例外狀況
key 為 null。
範例
下列程式代碼範例會列舉 的 HybridDictionary元素。
#using <System.dll>
using namespace System;
using namespace System::Collections;
using namespace System::Collections::Specialized;
void PrintKeysAndValues1( IDictionary^ myCol );
void PrintKeysAndValues2( IDictionary^ myCol );
void PrintKeysAndValues3( HybridDictionary^ myCol );
int main()
{
// Creates and initializes a new HybridDictionary.
HybridDictionary^ myCol = gcnew HybridDictionary;
myCol->Add( "Braeburn Apples", "1.49" );
myCol->Add( "Fuji Apples", "1.29" );
myCol->Add( "Gala Apples", "1.49" );
myCol->Add( "Golden Delicious Apples", "1.29" );
myCol->Add( "Granny Smith Apples", "0.89" );
myCol->Add( "Red Delicious Apples", "0.99" );
myCol->Add( "Plantain Bananas", "1.49" );
myCol->Add( "Yellow Bananas", "0.79" );
myCol->Add( "Strawberries", "3.33" );
myCol->Add( "Cranberries", "5.98" );
myCol->Add( "Navel Oranges", "1.29" );
myCol->Add( "Grapes", "1.99" );
myCol->Add( "Honeydew Melon", "0.59" );
myCol->Add( "Seedless Watermelon", "0.49" );
myCol->Add( "Pineapple", "1.49" );
myCol->Add( "Nectarine", "1.99" );
myCol->Add( "Plums", "1.69" );
myCol->Add( "Peaches", "1.99" );
// Display the contents of the collection using for each. This is the preferred method.
Console::WriteLine( "Displays the elements using for each:" );
PrintKeysAndValues1( myCol );
// Display the contents of the collection using the enumerator.
Console::WriteLine( "Displays the elements using the IDictionaryEnumerator:" );
PrintKeysAndValues2( myCol );
// Display the contents of the collection using the Keys, Values, Count, and Item properties.
Console::WriteLine( "Displays the elements using the Keys, Values, Count, and Item properties:" );
PrintKeysAndValues3( myCol );
}
// Uses the foreach statement which hides the complexity of the enumerator.
// NOTE: The foreach statement is the preferred way of enumerating the contents of a collection.
void PrintKeysAndValues1( IDictionary^ myCol ) {
Console::WriteLine( " KEY VALUE" );
for each ( DictionaryEntry^ de in myCol )
Console::WriteLine( " {0,-25} {1}", de->Key, de->Value );
Console::WriteLine();
}
// Uses the enumerator.
void PrintKeysAndValues2( IDictionary^ myCol )
{
IDictionaryEnumerator^ myEnumerator = myCol->GetEnumerator();
Console::WriteLine( " KEY VALUE" );
while ( myEnumerator->MoveNext() )
Console::WriteLine( " {0,-25} {1}", myEnumerator->Key, myEnumerator->Value );
Console::WriteLine();
}
// Uses the Keys, Values, Count, and Item properties.
void PrintKeysAndValues3( HybridDictionary^ myCol )
{
array<String^>^myKeys = gcnew array<String^>(myCol->Count);
myCol->Keys->CopyTo( myKeys, 0 );
Console::WriteLine( " INDEX KEY VALUE" );
for ( int i = 0; i < myCol->Count; i++ )
Console::WriteLine( " {0,-5} {1,-25} {2}", i, myKeys[ i ], myCol[ myKeys[ i ] ] );
Console::WriteLine();
}
/*
This code produces output similar to the following:
Displays the elements using for each:
KEY VALUE
Seedless Watermelon 0.49
Nectarine 1.99
Cranberries 5.98
Plantain Bananas 1.49
Honeydew Melon 0.59
Pineapple 1.49
Strawberries 3.33
Grapes 1.99
Braeburn Apples 1.49
Peaches 1.99
Red Delicious Apples 0.99
Golden Delicious Apples 1.29
Yellow Bananas 0.79
Granny Smith Apples 0.89
Gala Apples 1.49
Plums 1.69
Navel Oranges 1.29
Fuji Apples 1.29
Displays the elements using the IDictionaryEnumerator:
KEY VALUE
Seedless Watermelon 0.49
Nectarine 1.99
Cranberries 5.98
Plantain Bananas 1.49
Honeydew Melon 0.59
Pineapple 1.49
Strawberries 3.33
Grapes 1.99
Braeburn Apples 1.49
Peaches 1.99
Red Delicious Apples 0.99
Golden Delicious Apples 1.29
Yellow Bananas 0.79
Granny Smith Apples 0.89
Gala Apples 1.49
Plums 1.69
Navel Oranges 1.29
Fuji Apples 1.29
Displays the elements using the Keys, Values, Count, and Item properties:
INDEX KEY VALUE
0 Seedless Watermelon 0.49
1 Nectarine 1.99
2 Cranberries 5.98
3 Plantain Bananas 1.49
4 Honeydew Melon 0.59
5 Pineapple 1.49
6 Strawberries 3.33
7 Grapes 1.99
8 Braeburn Apples 1.49
9 Peaches 1.99
10 Red Delicious Apples 0.99
11 Golden Delicious Apples 1.29
12 Yellow Bananas 0.79
13 Granny Smith Apples 0.89
14 Gala Apples 1.49
15 Plums 1.69
16 Navel Oranges 1.29
17 Fuji Apples 1.29
*/
using System;
using System.Collections;
using System.Collections.Specialized;
public class SamplesHybridDictionary {
public static void Main() {
// Creates and initializes a new HybridDictionary.
HybridDictionary myCol = new HybridDictionary();
myCol.Add( "Braeburn Apples", "1.49" );
myCol.Add( "Fuji Apples", "1.29" );
myCol.Add( "Gala Apples", "1.49" );
myCol.Add( "Golden Delicious Apples", "1.29" );
myCol.Add( "Granny Smith Apples", "0.89" );
myCol.Add( "Red Delicious Apples", "0.99" );
myCol.Add( "Plantain Bananas", "1.49" );
myCol.Add( "Yellow Bananas", "0.79" );
myCol.Add( "Strawberries", "3.33" );
myCol.Add( "Cranberries", "5.98" );
myCol.Add( "Navel Oranges", "1.29" );
myCol.Add( "Grapes", "1.99" );
myCol.Add( "Honeydew Melon", "0.59" );
myCol.Add( "Seedless Watermelon", "0.49" );
myCol.Add( "Pineapple", "1.49" );
myCol.Add( "Nectarine", "1.99" );
myCol.Add( "Plums", "1.69" );
myCol.Add( "Peaches", "1.99" );
// Display the contents of the collection using foreach. This is the preferred method.
Console.WriteLine( "Displays the elements using foreach:" );
PrintKeysAndValues1( myCol );
// Display the contents of the collection using the enumerator.
Console.WriteLine( "Displays the elements using the IDictionaryEnumerator:" );
PrintKeysAndValues2( myCol );
// Display the contents of the collection using the Keys, Values, Count, and Item properties.
Console.WriteLine( "Displays the elements using the Keys, Values, Count, and Item properties:" );
PrintKeysAndValues3( myCol );
}
// Uses the foreach statement which hides the complexity of the enumerator.
// NOTE: The foreach statement is the preferred way of enumerating the contents of a collection.
public static void PrintKeysAndValues1( IDictionary myCol ) {
Console.WriteLine( " KEY VALUE" );
foreach ( DictionaryEntry de in myCol )
Console.WriteLine( " {0,-25} {1}", de.Key, de.Value );
Console.WriteLine();
}
// Uses the enumerator.
// NOTE: The foreach statement is the preferred way of enumerating the contents of a collection.
public static void PrintKeysAndValues2( IDictionary myCol ) {
IDictionaryEnumerator myEnumerator = myCol.GetEnumerator();
Console.WriteLine( " KEY VALUE" );
while ( myEnumerator.MoveNext() )
Console.WriteLine( " {0,-25} {1}", myEnumerator.Key, myEnumerator.Value );
Console.WriteLine();
}
// Uses the Keys, Values, Count, and Item properties.
public static void PrintKeysAndValues3( HybridDictionary myCol ) {
String[] myKeys = new String[myCol.Count];
myCol.Keys.CopyTo( myKeys, 0 );
Console.WriteLine( " INDEX KEY VALUE" );
for ( int i = 0; i < myCol.Count; i++ )
Console.WriteLine( " {0,-5} {1,-25} {2}", i, myKeys[i], myCol[myKeys[i]] );
Console.WriteLine();
}
}
/*
This code produces output similar to the following:
Displays the elements using foreach:
KEY VALUE
Seedless Watermelon 0.49
Nectarine 1.99
Cranberries 5.98
Plantain Bananas 1.49
Honeydew Melon 0.59
Pineapple 1.49
Strawberries 3.33
Grapes 1.99
Braeburn Apples 1.49
Peaches 1.99
Red Delicious Apples 0.99
Golden Delicious Apples 1.29
Yellow Bananas 0.79
Granny Smith Apples 0.89
Gala Apples 1.49
Plums 1.69
Navel Oranges 1.29
Fuji Apples 1.29
Displays the elements using the IDictionaryEnumerator:
KEY VALUE
Seedless Watermelon 0.49
Nectarine 1.99
Cranberries 5.98
Plantain Bananas 1.49
Honeydew Melon 0.59
Pineapple 1.49
Strawberries 3.33
Grapes 1.99
Braeburn Apples 1.49
Peaches 1.99
Red Delicious Apples 0.99
Golden Delicious Apples 1.29
Yellow Bananas 0.79
Granny Smith Apples 0.89
Gala Apples 1.49
Plums 1.69
Navel Oranges 1.29
Fuji Apples 1.29
Displays the elements using the Keys, Values, Count, and Item properties:
INDEX KEY VALUE
0 Seedless Watermelon 0.49
1 Nectarine 1.99
2 Cranberries 5.98
3 Plantain Bananas 1.49
4 Honeydew Melon 0.59
5 Pineapple 1.49
6 Strawberries 3.33
7 Grapes 1.99
8 Braeburn Apples 1.49
9 Peaches 1.99
10 Red Delicious Apples 0.99
11 Golden Delicious Apples 1.29
12 Yellow Bananas 0.79
13 Granny Smith Apples 0.89
14 Gala Apples 1.49
15 Plums 1.69
16 Navel Oranges 1.29
17 Fuji Apples 1.29
*/
Imports System.Collections
Imports System.Collections.Specialized
Public Class SamplesHybridDictionary
Public Shared Sub Main()
' Creates and initializes a new HybridDictionary.
Dim myCol As New HybridDictionary()
myCol.Add("Braeburn Apples", "1.49")
myCol.Add("Fuji Apples", "1.29")
myCol.Add("Gala Apples", "1.49")
myCol.Add("Golden Delicious Apples", "1.29")
myCol.Add("Granny Smith Apples", "0.89")
myCol.Add("Red Delicious Apples", "0.99")
myCol.Add("Plantain Bananas", "1.49")
myCol.Add("Yellow Bananas", "0.79")
myCol.Add("Strawberries", "3.33")
myCol.Add("Cranberries", "5.98")
myCol.Add("Navel Oranges", "1.29")
myCol.Add("Grapes", "1.99")
myCol.Add("Honeydew Melon", "0.59")
myCol.Add("Seedless Watermelon", "0.49")
myCol.Add("Pineapple", "1.49")
myCol.Add("Nectarine", "1.99")
myCol.Add("Plums", "1.69")
myCol.Add("Peaches", "1.99")
' Display the contents of the collection using For Each. This is the preferred method.
Console.WriteLine("Displays the elements using For Each:")
PrintKeysAndValues1(myCol)
' Display the contents of the collection using the enumerator.
Console.WriteLine("Displays the elements using the IDictionaryEnumerator:")
PrintKeysAndValues2(myCol)
' Display the contents of the collection using the Keys, Values, Count, and Item properties.
Console.WriteLine("Displays the elements using the Keys, Values, Count, and Item properties:")
PrintKeysAndValues3(myCol)
End Sub
' Uses the For Each statement which hides the complexity of the enumerator.
' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection.
Public Shared Sub PrintKeysAndValues1(myCol As IDictionary)
Console.WriteLine(" KEY VALUE")
Dim de As DictionaryEntry
For Each de In myCol
Console.WriteLine(" {0,-25} {1}", de.Key, de.Value)
Next de
Console.WriteLine()
End Sub
' Uses the enumerator.
' NOTE: The For Each statement is the preferred way of enumerating the contents of a collection.
Public Shared Sub PrintKeysAndValues2(myCol As IDictionary)
Dim myEnumerator As IDictionaryEnumerator = myCol.GetEnumerator()
Console.WriteLine(" KEY VALUE")
While myEnumerator.MoveNext()
Console.WriteLine(" {0,-25} {1}", myEnumerator.Key, myEnumerator.Value)
End While
Console.WriteLine()
End Sub
' Uses the Keys, Values, Count, and Item properties.
Public Shared Sub PrintKeysAndValues3(myCol As HybridDictionary)
Dim myKeys(myCol.Count) As [String]
myCol.Keys.CopyTo(myKeys, 0)
Console.WriteLine(" INDEX KEY VALUE")
Dim i As Integer
For i = 0 To myCol.Count - 1
Console.WriteLine(" {0,-5} {1,-25} {2}", i, myKeys(i), myCol(myKeys(i)))
Next i
Console.WriteLine()
End Sub
End Class
'This code produces output similar to the following:
'
'Displays the elements using For Each:
' KEY VALUE
' Seedless Watermelon 0.49
' Nectarine 1.99
' Cranberries 5.98
' Plantain Bananas 1.49
' Honeydew Melon 0.59
' Pineapple 1.49
' Strawberries 3.33
' Grapes 1.99
' Braeburn Apples 1.49
' Peaches 1.99
' Red Delicious Apples 0.99
' Golden Delicious Apples 1.29
' Yellow Bananas 0.79
' Granny Smith Apples 0.89
' Gala Apples 1.49
' Plums 1.69
' Navel Oranges 1.29
' Fuji Apples 1.29
'
'Displays the elements using the IDictionaryEnumerator:
' KEY VALUE
' Seedless Watermelon 0.49
' Nectarine 1.99
' Cranberries 5.98
' Plantain Bananas 1.49
' Honeydew Melon 0.59
' Pineapple 1.49
' Strawberries 3.33
' Grapes 1.99
' Braeburn Apples 1.49
' Peaches 1.99
' Red Delicious Apples 0.99
' Golden Delicious Apples 1.29
' Yellow Bananas 0.79
' Granny Smith Apples 0.89
' Gala Apples 1.49
' Plums 1.69
' Navel Oranges 1.29
' Fuji Apples 1.29
'
'Displays the elements using the Keys, Values, Count, and Item properties:
' INDEX KEY VALUE
' 0 Seedless Watermelon 0.49
' 1 Nectarine 1.99
' 2 Cranberries 5.98
' 3 Plantain Bananas 1.49
' 4 Honeydew Melon 0.59
' 5 Pineapple 1.49
' 6 Strawberries 3.33
' 7 Grapes 1.99
' 8 Braeburn Apples 1.49
' 9 Peaches 1.99
' 10 Red Delicious Apples 0.99
' 11 Golden Delicious Apples 1.29
' 12 Yellow Bananas 0.79
' 13 Granny Smith Apples 0.89
' 14 Gala Apples 1.49
' 15 Plums 1.69
' 16 Navel Oranges 1.29
' 17 Fuji Apples 1.29
備註
這個屬性可透過下列語法存取集合中的特定元素：myCollection[key]。
您也可以藉由設定不存在於 中的HybridDictionary索引鍵值，來使用 Item[] 屬性來加入新元素，例如 myCollection["myNonexistentKey"] = myValue。 不過，如果指定的索引鍵已存在於 中 HybridDictionary，則設定 Item[] 屬性會覆寫舊值。 相反地， Add 方法不會修改現有的專案。
索引鍵不能是 null，但值可以。 若要區別 null 傳回的 ，因為找不到指定的索引鍵，而且 null 因為指定索引鍵的值是 null傳回，請使用 Contains 方法來判斷索引鍵是否存在於清單中。
C# 語言會使用此 關鍵詞來定義索引器，而不是實作 Item[] 屬性。 Visual Basic 會將 Item[] 實作為預設屬性，這樣會提供相同的索引功能。
擷取此屬性的值是 O (1) 作業;設定 屬性也是 O (1) 作業。
