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CollectionBase.IList.Item-Eigenschaft

Aktualisiert: November 2007

Ruft das Element am angegebenen Index ab oder legt dieses fest.

Namespace:  System.Collections
Assembly:  mscorlib (in mscorlib.dll)

Object IList.Item[
	int index
] { get; set; }
J# unterstützt die Verwendung von expliziten Schnittstellenimplementierungen, aber nicht die Deklaration von neuen expliziten Schnittstellenimplementierungen.
JScript unterstützt keine expliziten Schnittstellenimplementierungen

Parameter

index
Typ: System.Int32
Der nullbasierte Index des Elements, das abgerufen oder festgelegt werden soll.

Eigenschaftenwert

Typ: System.Object
Das Element am angegebenen Index.

Implementiert

IList.Item[Int32]

AusnahmeBedingung
ArgumentOutOfRangeException

index ist kleiner als 0 (null).

- oder -

index ist größer oder gleich Count.

Diese Eigenschaft ermöglicht den Zugriff auf ein bestimmtes Element in der Auflistung mit folgender Syntax: myCollection[index].

Das Abrufen des Werts dieser Eigenschaft ist ebenso wie das Festlegen der Eigenschaft eine O(1)-Operation.

Hinweise zur Implementierung:

Wenn diese Eigenschaft festgelegt wird, werden die Methoden OnValidate, OnSet und OnSetComplete aufgerufen.

Im folgenden Codebeispiel wird die CollectionBase-Klasse implementiert und diese Implementierung zum Erstellen einer Auflistung von Int16-Objekten verwendet.

using System;
using System.Collections;

public class Int16Collection : CollectionBase  {

   public Int16 this[ int index ]  {
      get  {
         return( (Int16) List[index] );
      }
      set  {
         List[index] = value;
      }
   }

   public int Add( Int16 value )  {
      return( List.Add( value ) );
   }

   public int IndexOf( Int16 value )  {
      return( List.IndexOf( value ) );
   }

   public void Insert( int index, Int16 value )  {
      List.Insert( index, value );
   }

   public void Remove( Int16 value )  {
      List.Remove( value );
   }

   public bool Contains( Int16 value )  {
      // If value is not of type Int16, this will return false.
      return( List.Contains( value ) );
   }

   protected override void OnInsert( int index, Object value )  {
      // Insert additional code to be run only when inserting values.
   }

   protected override void OnRemove( int index, Object value )  {
      // Insert additional code to be run only when removing values.
   }

   protected override void OnSet( int index, Object oldValue, Object newValue )  {
      // Insert additional code to be run only when setting values.
   }

   protected override void OnValidate( Object value )  {
      if ( value.GetType() != typeof(System.Int16) )
         throw new ArgumentException( "value must be of type Int16.", "value" );
   }

}


public class SamplesCollectionBase  {

   public static void Main()  {

      // Create and initialize a new CollectionBase.
      Int16Collection myI16 = new Int16Collection();

      // Add elements to the collection.
      myI16.Add( (Int16) 1 );
      myI16.Add( (Int16) 2 );
      myI16.Add( (Int16) 3 );
      myI16.Add( (Int16) 5 );
      myI16.Add( (Int16) 7 );

      // Display the contents of the collection using foreach. This is the preferred method.
      Console.WriteLine( "Contents of the collection (using foreach):" );
      PrintValues1( myI16 );

      // Display the contents of the collection using the enumerator.
      Console.WriteLine( "Contents of the collection (using enumerator):" );
      PrintValues2( myI16 );

      // Display the contents of the collection using the Count property and the Item property.
      Console.WriteLine( "Initial contents of the collection (using Count and Item):" );
      PrintIndexAndValues( myI16 );

      // Search the collection with Contains and IndexOf.
      Console.WriteLine( "Contains 3: {0}", myI16.Contains( 3 ) );
      Console.WriteLine( "2 is at index {0}.", myI16.IndexOf( 2 ) );
      Console.WriteLine();

      // Insert an element into the collection at index 3.
      myI16.Insert( 3, (Int16) 13 );
      Console.WriteLine( "Contents of the collection after inserting at index 3:" );
      PrintIndexAndValues( myI16 );

      // Get and set an element using the index.
      myI16[4] = 123;
      Console.WriteLine( "Contents of the collection after setting the element at index 4 to 123:" );
      PrintIndexAndValues( myI16 );

      // Remove an element from the collection.
      myI16.Remove( (Int16) 2 );

      // Display the contents of the collection using the Count property and the Item property.
      Console.WriteLine( "Contents of the collection after removing the element 2:" );
      PrintIndexAndValues( myI16 );

   }

   // Uses the Count property and the Item property.
   public static void PrintIndexAndValues( Int16Collection myCol )  {
      for ( int i = 0; i < myCol.Count; i++ )
         Console.WriteLine( "   [{0}]:   {1}", i, myCol[i] );
      Console.WriteLine();
   }

   // 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 PrintValues1( Int16Collection myCol )  {
      foreach ( Int16 i16 in myCol )
         Console.WriteLine( "   {0}", i16 );
      Console.WriteLine();
   }

   // Uses the enumerator. 
   // NOTE: The foreach statement is the preferred way of enumerating the contents of a collection.
   public static void PrintValues2( Int16Collection myCol )  {
      System.Collections.IEnumerator myEnumerator = myCol.GetEnumerator();
      while ( myEnumerator.MoveNext() )
         Console.WriteLine( "   {0}", myEnumerator.Current );
      Console.WriteLine();
   }
}


/* 
This code produces the following output.

Contents of the collection (using foreach):
   1
   2
   3
   5
   7

Contents of the collection (using enumerator):
   1
   2
   3
   5
   7

Initial contents of the collection (using Count and Item):
   [0]:   1
   [1]:   2
   [2]:   3
   [3]:   5
   [4]:   7

Contains 3: True
2 is at index 1.

Contents of the collection after inserting at index 3:
   [0]:   1
   [1]:   2
   [2]:   3
   [3]:   13
   [4]:   5
   [5]:   7

Contents of the collection after setting the element at index 4 to 123:
   [0]:   1
   [1]:   2
   [2]:   3
   [3]:   13
   [4]:   123
   [5]:   7

Contents of the collection after removing the element 2:
   [0]:   1
   [1]:   3
   [2]:   13
   [3]:   123
   [4]:   7

*/



import System.* ;
import System.Collections.*;
import System.Collections.CollectionBase.*;

public class Int16Collection extends CollectionBase
{
    /** @property 
     */
    public short get_Value(int index)
    {
        short s = System.Convert.ToInt16(get_List().get_Item(index));
        return(s) ; 
    } //get_Value

    /** @property 
     */
    public void set_Value(int index,short value)
    {
        get_List().set_Item(index, (Int16)value);
    } //set_Value

    public int Add(short value) 
    {
        return get_List().Add((Int16)value);
    } //Add

    public int IndexOf(short value)
    {
        return get_List().IndexOf((Int16)value);
    } //IndexOf

    public void Insert(int index, short value) 
    {
        get_List().Insert(index, (Int16)value);
    } //Insert

    public void Remove(short value) 
    {
        get_List().Remove((Int16)value);
    } //Remove

    public boolean Contains(short value) 
    {
        // If value is not of type Int16, this will return false.
        return get_List().Contains((Int16)value);
    } //Contains

    protected   void OnInsert(int index, Object value) 
    {
        // Insert additional code to be run only when inserting values.
    } //OnInsert

       protected   void OnRemove(int index, Object value) 
    {
        // Insert additional code to be run only when removing values.
    } //OnRemove

       protected   void OnSet(int index, Object oldValue, Object newValue) 
    {
        // Insert additional code to be run only when setting values.
    } //OnSet

    protected   void OnValidate(Object value) 
    {
        if ( value.GetType() != Type.GetType("System.Int16")  ) {
            throw new ArgumentException("value must be of type Int16.", 
                "value");
        }
    } //OnValidate
} //Int16Collection

public class SamplesCollectionBase
{
    public static void main(String[] args)
    {
        // Create and initialize a new CollectionBase.
        Int16Collection myI16 =  new Int16Collection();

        // Add elements to the collection.
        myI16.Add((Int16)1);
        myI16.Add((Int16)2);
        myI16.Add((Int16)3);
        myI16.Add((Int16)5);
        myI16.Add((Int16)7);

        // Display the contents of the collection using for.
        Console.WriteLine("Contents of the collection (using for):");
        PrintValues1(myI16);

        // Display the contents of the collection using the enumerator.
        Console.WriteLine("Contents of the collection (using enumerator):");
        PrintValues2(myI16);

        // Display the contents of the collection using the Count property and 
        // the Item property.
        Console.WriteLine("Initial contents of the collection "
            + "(using Count and Item):");
        PrintIndexAndValues(myI16);

        // Search the collection with Contains and IndexOf.
        Console.WriteLine("Contains 3: {0}", 
            (System.Boolean)myI16.Contains((Int16)3));
        Console.WriteLine("2 is at index {0}.", 
            (Int16)myI16.IndexOf((Int16)2));
        Console.WriteLine();

        // Insert an element into the collection at index 3.
        myI16.Insert(3, (Int16)13);
        Console.WriteLine("Contents of the collection after inserting at"
            + " index 3:");
        PrintIndexAndValues(myI16);

        // Get and set an element using the index.
        myI16 .set_Item( 4 ,(Int16)123 );
        Console.WriteLine("Contents of the collection after setting the"
            + " element at index 4 to 123:");
        PrintIndexAndValues(myI16);

        // Remove an element from the collection.
        myI16.Remove((Int16)2);

        // Display the contents of the collection using the Count property and
        // the Item property.
        Console.WriteLine("Contents of the collection after removing the"
            + " element 2:");
        PrintIndexAndValues(myI16);
   } //main

   // Uses the Count property and the Item property.
    public static void PrintIndexAndValues(Int16Collection myCol) 
    {
        for(int i = 0; i < myCol.get_Count(); i++) {
            Console.WriteLine("   [{0}]:   {1}", (Int32)i, 
                myCol.get_Item(i));
        } 
        Console.WriteLine();
    } //PrintIndexAndValues

    // Uses the for statement which hides the complexity of the enumerator.
    // NOTE: The for statement is the preferred way of enumerating the contents 
    // of a collection.
    public static void PrintValues1(Int16Collection myCol) 
    {
        for (int iCtr = 0; iCtr < myCol.get_Count(); iCtr++) {
            Console.WriteLine("   {0}", myCol.get_Item(iCtr));
        }
        Console.WriteLine();
    } //PrintValues1

    // Uses the enumerator. 
    // NOTE: The for statement is the preferred way of enumerating the contents 
    // of a collection.
    public static void PrintValues2(Int16Collection myCol) 
    {
        System.Collections.IEnumerator myEnumerator = myCol.GetEnumerator();
        while(myEnumerator.MoveNext()) {
            Console.WriteLine("   {0}", myEnumerator.get_Current());
        }
        Console.WriteLine();
    } //PrintValues2
} //SamplesCollectionBase

/* 
Contents of the collection (using for):
   1
   2
   3
   5
   7

Contents of the collection (using enumerator):
   1
   2
   3
   5
   7

Initial contents of the collection (using Count and Item):
   [0]:   1
   [1]:   2
   [2]:   3
   [3]:   5
   [4]:   7

Contains 3: True
2 is at index 1.

Contents of the collection after inserting at index 3:
   [0]:   1
   [1]:   2
   [2]:   3
   [3]:   13
   [4]:   5
   [5]:   7

Contents of the collection after setting the element at index 4 to 123:
   [0]:   1
   [1]:   2
   [2]:   3
   [3]:   13
   [4]:   123
   [5]:   7

Contents of the collection after removing the element 2:
   [0]:   1
   [1]:   3
   [2]:   13
   [3]:   123
   [4]:   7

*/



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