KeyedCollection<TKey,TItem>.ChangeItemKey(TItem, TKey) Methode

Referenz

Definition

Namespace:: System.Collections.ObjectModel

Assembly:: System.ObjectModel.dll

Assembly:: mscorlib.dll

Assembly:: netstandard.dll

Quelle:: KeyedCollection.cs

Quelle:: KeyedCollection.cs

Quelle:: KeyedCollection.cs

Wichtig

Einige Informationen beziehen sich auf Vorabversionen, die vor dem Release ggf. grundlegend überarbeitet werden. Microsoft übernimmt hinsichtlich der hier bereitgestellten Informationen keine Gewährleistungen, seien sie ausdrücklich oder konkludent.

Ändert den dem angegebenen Element im Suchwörterbuch zugeordneten Schlüssel.

protected:
 void ChangeItemKey(TItem item, TKey newKey);

protected void ChangeItemKey (TItem item, TKey newKey);

member this.ChangeItemKey : 'Item * 'Key -> unit

Protected Sub ChangeItemKey (item As TItem, newKey As TKey)

Parameter

item: TItem

Das Element, dessen Schlüssel geändert werden soll.

newKey: TKey

Der neue Schlüssel für item.

Ausnahmen

ArgumentNullException

item ist null.

- oder -

key ist null.

ArgumentException

item wurde nicht gefunden.

- oder -

key ist bereits in der KeyedCollection<TKey,TItem> vorhanden.

Beispiele

Das folgende Codebeispiel zeigt, wie die geschützte ChangeItemKey Methode zur Unterstützung veränderlicher Schlüssel überschrieben wird und wie die geschützten InsertItemMethoden , RemoveItem, , ClearItemsund SetItem überschrieben werden, um die Integrität der Schlüssel und der Auflistung zu erhalten.

Im Codebeispiel wird die MutableKeys Auflistung erstellt, die von abgeleitet wird KeyedCollection<TKey,TItem>, und der MutableKey -Klasse. Die MutableKey -Klasse verfügt über eine settable-Eigenschaft Key . Wenn der -Eigenschaft ein neuer Schlüssel zugewiesen wird, ruft der Eigenschaftensetter die internalChangeKey -Methode der Auflistung auf, um zu testen, ob der neue Schlüssel mit einem vorhandenen Schlüssel in Konflikt steht. Wenn ja, wird eine Ausnahme ausgelöst, und der Eigenschaftswert wird nicht geändert.

Um die Verbindung zwischen einem MutableKey Objekt und der MutableKeys Auflistung aufrechtzuerhalten und zu verhindern, dass ein Objekt in zwei Auflistungen eingefügt wird, verfügt die MutableKey Klasse über ein internalCollection Feld. Dieses Feld wird von den geschützten Methoden verwaltet, die benutzerdefiniertes Verhalten zum Hinzufügen und Entfernen von Elementen aus der Auflistung bereitstellen, z. B. die InsertItem -Methode. Das Feld wird festgelegt, wenn das Element einer Auflistung hinzugefügt und gelöscht wird, wenn das Element entfernt wird.

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

// This class demonstrates one way to use the ChangeItemKey
// method to store objects with keys that can be changed. The
// ChangeItemKey method is used to keep the internal lookup
// Dictionary in sync with the keys of the stored objects.
//
// MutableKeys stores MutableKey objects, which have an Integer
// Key property that can be set. Therefore, MutableKeys inherits
// KeyedCollection(Of Integer, MutableKey).
//
public class MutableKeys : KeyedCollection<int, MutableKey>
{
    // This parameterless constructor delegates to the base class
    // constructor that specifies a dictionary threshold. A
    // threshold of 0 means the internal Dictionary is created
    // the first time an object is added.
    //
    public MutableKeys() : base(null, 0) {}

    protected override int GetKeyForItem(MutableKey item)
    {
        // The key is MutableKey.Key.
        return item.Key;
    }

    protected override void InsertItem(int index, MutableKey newItem)
    {
        if (newItem.Collection != null)
            throw new ArgumentException("The item already belongs to a collection.");

        base.InsertItem(index, newItem);
        newItem.Collection = this;
    }

    protected override void SetItem(int index, MutableKey newItem)
    {
        MutableKey replaced = Items[index];

        if (newItem.Collection != null)
            throw new ArgumentException("The item already belongs to a collection.");

        base.SetItem(index, newItem);
        newItem.Collection = this;
        replaced.Collection = null;
    }

    protected override void RemoveItem(int index)
    {
        MutableKey removedItem = Items[index];

        base.RemoveItem(index);
        removedItem.Collection = null;
    }

    protected override void ClearItems()
    {
        foreach( MutableKey mk in Items )
        {
            mk.Collection = null;
        }

        base.ClearItems();
    }

    internal void ChangeKey(MutableKey item, int newKey)
    {
        base.ChangeItemKey(item, newKey);
    }

    public void Dump()
    {
        Console.WriteLine("\nDUMP:");
        if (Dictionary == null)
        {
            Console.WriteLine("    The dictionary has not been created.");
        }
        else
        {
            Console.WriteLine("    Dictionary entries");
            Console.WriteLine("    ------------------");

            foreach( KeyValuePair<int, MutableKey> kvp in Dictionary )
            {
                Console.WriteLine("    {0} : {1}", kvp.Key, kvp.Value);
            }
        }

        Console.WriteLine("\n    List of items");
        Console.WriteLine("    -------------");

        foreach( MutableKey mk in Items )
        {
            Console.WriteLine("    {0}", mk);
        }
    }
}

public class Demo
{
    public static void Main()
    {
        MutableKeys mkeys = new MutableKeys();

        // The Add method is inherited from Collection.
        //
        mkeys.Add(new MutableKey(110072674, "Widget"));
        mkeys.Add(new MutableKey(110072675, "Sprocket"));

        mkeys.Dump();

        Console.WriteLine("\nCreate and insert a new item:");
        MutableKey test = new MutableKey(110072684, "Gear");
        mkeys.Insert(1, test);

        mkeys.Dump();

        try
        {
            Console.WriteLine("\nTry to insert the item again:");
            mkeys.Insert(1, test);
        }
        catch(ArgumentException ex)
        {
            Console.WriteLine("Error: {0}", ex.Message);
        }

        Console.WriteLine("\nChange the Key property of the item:");
        test.Key = 100000072;

        mkeys.Dump();

        try
        {
            Console.WriteLine("\nTry to set the Key property to an existing key:");
            test.Key = 110072674;
        }
        catch(ArgumentException ex)
        {
            Console.WriteLine("Error: {0}", ex.Message);
        }

        mkeys.Dump();
    }

    private static void Display(MutableKeys order)
    {
        Console.WriteLine();
        foreach( MutableKey item in order )
        {
            Console.WriteLine(item);
        }
    }
}

// This class has a key that can be changed.
//
public class MutableKey
{

    public MutableKey(int newKey, string newValue)
    {
        _key = newKey;
        Value = newValue;
    } //New

    public string Value;
    internal MutableKeys Collection;

    private int _key;
    public int Key
    {
        get
        {
            return _key;
        }
        set
        {
            if (Collection != null)
            {
                Collection.ChangeKey(this, value);
            }

            _key = value;
        }
    }

    public override string ToString()
    {
        return String.Format("{0,9} {1}", _key, Value);
    }
}

/* This code example produces the following output:

DUMP:
    Dictionary entries
    ------------------
    110072674 : 110072674 Widget
    110072675 : 110072675 Sprocket

    List of items
    -------------
    110072674 Widget
    110072675 Sprocket

Create and insert a new item:

DUMP:
    Dictionary entries
    ------------------
    110072674 : 110072674 Widget
    110072675 : 110072675 Sprocket
    110072684 : 110072684 Gear

    List of items
    -------------
    110072674 Widget
    110072684 Gear
    110072675 Sprocket

Try to insert the item again:
Error: The item already belongs to a collection.

Change the Key property of the item:

DUMP:
    Dictionary entries
    ------------------
    110072674 : 110072674 Widget
    110072675 : 110072675 Sprocket
    100000072 : 100000072 Gear

    List of items
    -------------
    110072674 Widget
    100000072 Gear
    110072675 Sprocket

Try to set the Key property to an existing key:
Error: An item with the same key has already been added.

DUMP:
    Dictionary entries
    ------------------
    110072674 : 110072674 Widget
    110072675 : 110072675 Sprocket
    100000072 : 100000072 Gear

    List of items
    -------------
    110072674 Widget
    100000072 Gear
    110072675 Sprocket
 */

Imports System.Collections.Generic
Imports System.Collections.ObjectModel

' This class demonstrates one way to use the ChangeItemKey
' method to store objects with keys that can be changed. The 
' ChangeItemKey method is used to keep the internal lookup
' Dictionary in sync with the keys of the stored objects. 
'
' MutableKeys stores MutableKey objects, which have an Integer
' Key property that can be set. Therefore, MutableKeys inherits
' KeyedCollection(Of Integer, MutableKey).
'
Public Class MutableKeys
    Inherits KeyedCollection(Of Integer, MutableKey)

    ' This parameterless constructor delegates to the base class 
    ' constructor that specifies a dictionary threshold. A
    ' threshold of 0 means the internal Dictionary is created
    ' the first time an object is added.
    '
    Public Sub New()
        MyBase.New(Nothing, 0)
    End Sub
    
    Protected Overrides Function GetKeyForItem( _
        ByVal item As MutableKey) As Integer

        ' The key is MutableKey.Key.
        Return item.Key   
    End Function

    Protected Overrides Sub InsertItem( _
        ByVal index As Integer, ByVal newItem As MutableKey)

        If newItem.Collection IsNot Nothing Then _
            Throw New ArgumentException("The item already belongs to a collection.")

        MyBase.InsertItem(index, newItem)
        newItem.Collection = Me
    End Sub

    Protected Overrides Sub SetItem(ByVal index As Integer, _
        ByVal newItem As MutableKey)

        Dim replaced As MutableKey = Items(index)

        If newItem.Collection IsNot Nothing Then _
            Throw New ArgumentException("The item already belongs to a collection.")

        MyBase.SetItem(index, newItem)
        newItem.Collection = Me
        replaced.Collection = Nothing
    End Sub

    Protected Overrides Sub RemoveItem(ByVal index As Integer)
        Dim removedItem As MutableKey = Items(index)

        MyBase.RemoveItem(index)
        removedItem.Collection = Nothing
    End Sub

    Protected Overrides Sub ClearItems()
        For Each mk As MutableKey In Items
            mk.Collection = Nothing
        Next
        
        MyBase.ClearItems()
    End Sub

    Friend Sub ChangeKey(ByVal item As MutableKey, _
        ByVal newKey As Integer)

        MyBase.ChangeItemKey(item, newKey)
    End Sub
    
    Public Sub Dump()
        Console.WriteLine(vbLf & "DUMP:")
        If Dictionary Is Nothing Then
            Console.WriteLine("    The dictionary has not been created.")
        Else
            Console.WriteLine("    Dictionary entries")
            Console.WriteLine("    ------------------")

            For Each kvp As KeyValuePair(Of Integer, MutableKey) In Dictionary
                Console.WriteLine("    {0} : {1}", kvp.Key, kvp.Value)
            Next
        End If

        Console.WriteLine(vbLf & "    List of items")
        Console.WriteLine("    -------------")

        For Each mk As MutableKey In Items
            Console.WriteLine("    {0}", mk)
        Next
    End Sub

End Class

Public Class Demo
    
    Public Shared Sub Main() 

        Dim mkeys As New MutableKeys()

        ' The Add method is inherited from Collection.
        '
        mkeys.Add(New MutableKey(110072674, "Widget"))
        mkeys.Add(New MutableKey(110072675, "Sprocket"))

        mkeys.Dump() 
    
        Console.WriteLine(vbLf & "Create and insert a new item:")
        Dim test As New MutableKey(110072684, "Gear")
        mkeys.Insert(1, test)

        mkeys.Dump()

        Try
            Console.WriteLine(vbLf & "Try to insert the item again:")
            mkeys.Insert(1, test)
        Catch ex As ArgumentException
            Console.WriteLine("Error: {0}", ex.Message)
        End Try

        Console.WriteLine(vbLf & "Change the Key property of the item:")
        test.Key = 100000072

        mkeys.Dump()

        Try
            Console.WriteLine(vbLf & "Try to set the Key property to an existing key:")
            test.Key = 110072674
        Catch ex As ArgumentException
            Console.WriteLine("Error: {0}", ex.Message)
        End Try

        mkeys.Dump()

    End Sub
    
    Private Shared Sub Display(ByVal order As MutableKeys) 
        Console.WriteLine()
        For Each item As MutableKey In  order
            Console.WriteLine(item)
        Next item
    End Sub
End Class

' This class has a key that can be changed.
' 
Public Class MutableKey

    Public Sub New(ByVal newKey As Integer, ByVal newValue As String)
        _key = newKey
        Value = newValue
    End Sub
    
    Public Value As String
    Friend Collection As MutableKeys
    
    Private _key As Integer
    Public Property Key As Integer 
        Get
            Return _key
        End Get
        Set
            If Collection IsNot Nothing Then
                Collection.ChangeKey(Me, value)
            End If

            _key = value
        End Set
    End Property

    Public Overrides Function ToString() As String 
        Return String.Format("{0,9} {1}", _key, Value)
    End Function
        
End Class

' This code example produces the following output:
'
'DUMP:
'    Dictionary entries
'    ------------------
'    110072674 : 110072674 Widget
'    110072675 : 110072675 Sprocket
'
'    List of items
'    -------------
'    110072674 Widget
'    110072675 Sprocket
'
'Create and insert a new item:
'
'DUMP:
'    Dictionary entries
'    ------------------
'    110072674 : 110072674 Widget
'    110072675 : 110072675 Sprocket
'    110072684 : 110072684 Gear
'
'    List of items
'    -------------
'    110072674 Widget
'    110072684 Gear
'    110072675 Sprocket
'
'Try to insert the item again:
'Error: The item already belongs to a collection.
'
'Change the Key property of the item:
'
'DUMP:
'    Dictionary entries
'    ------------------
'    110072674 : 110072674 Widget
'    110072675 : 110072675 Sprocket
'    100000072 : 100000072 Gear
'
'    List of items
'    -------------
'    110072674 Widget
'    100000072 Gear
'    110072675 Sprocket
'
'Try to set the Key property to an existing key:
'Error: An item with the same key has already been added.
'
'DUMP:
'    Dictionary entries
'    ------------------
'    110072674 : 110072674 Widget
'    110072675 : 110072675 Sprocket
'    100000072 : 100000072 Gear
'
'    List of items
'    -------------
'    110072674 Widget
'    100000072 Gear
'    110072675 Sprocket

Hinweise

Weitere Informationen zu dieser API finden Sie unter Zusätzliche API-Hinweise für KeyedCollection<TKey,TItem>. ChangeItemKey.

Gilt für: