HybridDictionary.Item[Object] Vlastnost
Definice
Důležité
Některé informace platí pro předběžně vydaný produkt, který se může zásadně změnit, než ho výrobce nebo autor vydá. Microsoft neposkytuje žádné záruky, výslovné ani předpokládané, týkající se zde uváděných informací.
Získá nebo nastaví hodnotu přidruženou k zadanému klíči.
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 ObjectParametry
- key
- Object
Klíč, jehož hodnotu chcete získat nebo nastavit.
Hodnota vlastnosti
Hodnota přidružená k zadanému klíči. Pokud se zadaný klíč nenajde, při pokusu o jeho získání se vrátí nulla při pokusu o jeho nastavení se vytvoří nová položka pomocí zadaného klíče.
Implementuje
Výjimky
key je null.
Příklady
Následující příklad kódu vytvoří výčet prvků objektu HybridDictionary.
#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
Poznámky
Tato vlastnost poskytuje možnost přístupu ke konkrétnímu prvku v kolekci pomocí následující syntaxe: myCollection[key].
Vlastnost můžete také použít Item[] k přidání nových prvků nastavením hodnoty klíče, který v objektu HybridDictionaryneexistuje, myCollection["myNonexistentKey"] = myValuenapříklad . Pokud však zadaný klíč již existuje v HybridDictionary, nastavení Item[] vlastnosti přepíše starou hodnotu. Naproti tomu Add metoda neupravuje existující prvky.
Klíč nemůže být null, ale hodnota může být . Chcete-li rozlišovat mezi null vrácenou hodnotou, protože zadaný klíč nebyl nalezen a null který je vrácen, protože hodnota zadaného klíče je null, pomocí Contains metody zjistěte, zda klíč existuje v seznamu.
Jazyk C# používá toto klíčové slovo k definování indexerů místo implementace Item[] vlastnosti . Visual Basic implementuje Item[] jako výchozí vlastnost, která poskytuje stejné funkce indexování.
Načtení hodnoty této vlastnosti je O(1) operace; nastavení vlastnosti je také operace O(1).
Platí pro
Viz také
Spolupracujte s námi na GitHubu
Zdroj tohoto obsahu najdete na GitHubu, kde můžete také vytvářet a kontrolovat problémy a žádosti o přijetí změn. Další informace najdete v našem průvodci pro přispěvatele.
