Collection<T>.ClearItems メソッド

protected:
 virtual void ClearItems();

protected virtual void ClearItems ();

abstract member ClearItems : unit -> unit
override this.ClearItems : unit -> unit

Protected Overridable Sub ClearItems ()

例

次のコード例は、ジェネリック クラスのCollection<T>構築された型からコレクション クラスを派生させる方法と、保護された InsertItem、RemoveItem、ClearItems、および SetItem の各メソッドをオーバーライドして、 プロパティを設定するためのAddRemoveInsertClearカスタム動作を提供する方法をItem[]示しています。

この例で提供されるカスタム動作は、 Changed 保護された各メソッドの最後に発生する通知イベントです。 クラスは Dinosaurs (Collection(Of String) Visual Basic では ) を継承Collection<string>し、イベントをChanged定義します。イベントは、イベント情報のクラスと、変更の種類を識別する列挙体を使用DinosaursChangedEventArgsします。

このコード例では、 のいくつかのプロパティと メソッドを Collection<T> 呼び出して、カスタム イベントを示します。

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

public class Dinosaurs : Collection<string>
{
    public event EventHandler<DinosaursChangedEventArgs> Changed;

    protected override void InsertItem(int index, string newItem)
    {
        base.InsertItem(index, newItem);

        EventHandler<DinosaursChangedEventArgs> temp = Changed;
        if (temp != null)
        {
            temp(this, new DinosaursChangedEventArgs(
                ChangeType.Added, newItem, null));
        }
    }

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

        EventHandler<DinosaursChangedEventArgs> temp = Changed;
        if (temp != null)
        {
            temp(this, new DinosaursChangedEventArgs(
                ChangeType.Replaced, replaced, newItem));
        }
    }

    protected override void RemoveItem(int index)
    {
        string removedItem = Items[index];
        base.RemoveItem(index);

        EventHandler<DinosaursChangedEventArgs> temp = Changed;
        if (temp != null)
        {
            temp(this, new DinosaursChangedEventArgs(
                ChangeType.Removed, removedItem, null));
        }
    }

    protected override void ClearItems()
    {
        base.ClearItems();

        EventHandler<DinosaursChangedEventArgs> temp = Changed;
        if (temp != null)
        {
            temp(this, new DinosaursChangedEventArgs(
                ChangeType.Cleared, null, null));
        }
    }
}

// Event argument for the Changed event.
//
public class DinosaursChangedEventArgs : EventArgs
{
    public readonly string ChangedItem;
    public readonly ChangeType ChangeType;
    public readonly string ReplacedWith;

    public DinosaursChangedEventArgs(ChangeType change, string item,
        string replacement)
    {
        ChangeType = change;
        ChangedItem = item;
        ReplacedWith = replacement;
    }
}

public enum ChangeType
{
    Added,
    Removed,
    Replaced,
    Cleared
};

public class Demo
{
    public static void Main()
    {
        Dinosaurs dinosaurs = new Dinosaurs();

        dinosaurs.Changed += ChangedHandler;

        dinosaurs.Add("Psitticosaurus");
        dinosaurs.Add("Caudipteryx");
        dinosaurs.Add("Compsognathus");
        dinosaurs.Add("Muttaburrasaurus");

        Display(dinosaurs);

        Console.WriteLine("\nIndexOf(\"Muttaburrasaurus\"): {0}",
            dinosaurs.IndexOf("Muttaburrasaurus"));

        Console.WriteLine("\nContains(\"Caudipteryx\"): {0}",
            dinosaurs.Contains("Caudipteryx"));

        Console.WriteLine("\nInsert(2, \"Nanotyrannus\")");
        dinosaurs.Insert(2, "Nanotyrannus");

        Console.WriteLine("\ndinosaurs[2]: {0}", dinosaurs[2]);

        Console.WriteLine("\ndinosaurs[2] = \"Microraptor\"");
        dinosaurs[2] = "Microraptor";

        Console.WriteLine("\nRemove(\"Microraptor\")");
        dinosaurs.Remove("Microraptor");

        Console.WriteLine("\nRemoveAt(0)");
        dinosaurs.RemoveAt(0);

        Display(dinosaurs);
    }

    private static void Display(Collection<string> cs)
    {
        Console.WriteLine();
        foreach( string item in cs )
        {
            Console.WriteLine(item);
        }
    }

    private static void ChangedHandler(object source,
        DinosaursChangedEventArgs e)
    {

        if (e.ChangeType==ChangeType.Replaced)
        {
            Console.WriteLine("{0} was replaced with {1}", e.ChangedItem,
                e.ReplacedWith);
        }
        else if(e.ChangeType==ChangeType.Cleared)
        {
            Console.WriteLine("The dinosaur list was cleared.");
        }
        else
        {
            Console.WriteLine("{0} was {1}.", e.ChangedItem, e.ChangeType);
        }
    }
}

/* This code example produces the following output:

Psitticosaurus was Added.
Caudipteryx was Added.
Compsognathus was Added.
Muttaburrasaurus was Added.

Psitticosaurus
Caudipteryx
Compsognathus
Muttaburrasaurus

IndexOf("Muttaburrasaurus"): 3

Contains("Caudipteryx"): True

Insert(2, "Nanotyrannus")
Nanotyrannus was Added.

dinosaurs[2]: Nanotyrannus

dinosaurs[2] = "Microraptor"
Nanotyrannus was replaced with Microraptor

Remove("Microraptor")
Microraptor was Removed.

RemoveAt(0)
Psitticosaurus was Removed.

Caudipteryx
Compsognathus
Muttaburrasaurus
 */

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

Public Class Dinosaurs
    Inherits Collection(Of String)

    Public Event Changed As EventHandler(Of DinosaursChangedEventArgs)

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

        MyBase.InsertItem(index, newItem)

        RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _
            ChangeType.Added, newItem, Nothing))
    End Sub

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

        Dim replaced As String = Items(index)
        MyBase.SetItem(index, newItem)

        RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _
            ChangeType.Replaced, replaced, newItem))
    End Sub

    Protected Overrides Sub RemoveItem(ByVal index As Integer)

        Dim removedItem As String = Items(index)
        MyBase.RemoveItem(index)

        RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _
            ChangeType.Removed, removedItem, Nothing))
    End Sub

    Protected Overrides Sub ClearItems()
        MyBase.ClearItems()

        RaiseEvent Changed(Me, New DinosaursChangedEventArgs( _
            ChangeType.Cleared, Nothing, Nothing))
    End Sub

End Class

' Event argument for the Changed event.
'
Public Class DinosaursChangedEventArgs
    Inherits EventArgs

    Public ReadOnly ChangedItem As String
    Public ReadOnly ChangeType As ChangeType
    Public ReadOnly ReplacedWith As String

    Public Sub New(ByVal change As ChangeType, ByVal item As String, _
        ByVal replacement As String)

        ChangeType = change
        ChangedItem = item
        ReplacedWith = replacement
    End Sub
End Class

Public Enum ChangeType
    Added
    Removed
    Replaced
    Cleared
End Enum

Public Class Demo
    
    Public Shared Sub Main() 

        Dim dinosaurs As New Dinosaurs

        AddHandler dinosaurs.Changed, AddressOf ChangedHandler

        dinosaurs.Add("Psitticosaurus")
        dinosaurs.Add("Caudipteryx")
        dinosaurs.Add("Compsognathus")
        dinosaurs.Add("Muttaburrasaurus")

        Display(dinosaurs)
    
        Console.WriteLine(vbLf & "IndexOf(""Muttaburrasaurus""): {0}", _
            dinosaurs.IndexOf("Muttaburrasaurus"))

        Console.WriteLine(vbLf & "Contains(""Caudipteryx""): {0}", _
            dinosaurs.Contains("Caudipteryx"))

        Console.WriteLine(vbLf & "Insert(2, ""Nanotyrannus"")")
        dinosaurs.Insert(2, "Nanotyrannus")

        Console.WriteLine(vbLf & "dinosaurs(2): {0}", dinosaurs(2))

        Console.WriteLine(vbLf & "dinosaurs(2) = ""Microraptor""")
        dinosaurs(2) = "Microraptor"

        Console.WriteLine(vbLf & "Remove(""Microraptor"")")
        dinosaurs.Remove("Microraptor")

        Console.WriteLine(vbLf & "RemoveAt(0)")
        dinosaurs.RemoveAt(0)

        Display(dinosaurs)
 
    End Sub
    
    Private Shared Sub Display(ByVal cs As Collection(Of String)) 
        Console.WriteLine()
        For Each item As String In cs
            Console.WriteLine(item)
        Next item
    End Sub

    Private Shared Sub ChangedHandler(ByVal source As Object, _
        ByVal e As DinosaursChangedEventArgs)

        If e.ChangeType = ChangeType.Replaced Then
            Console.WriteLine("{0} was replaced with {1}", _
                e.ChangedItem, e.ReplacedWith)

        ElseIf e.ChangeType = ChangeType.Cleared Then
            Console.WriteLine("The dinosaur list was cleared.")

        Else
            Console.WriteLine("{0} was {1}.", _
                e.ChangedItem, e.ChangeType)
        End If
    End Sub

End Class

' This code example produces the following output:
'
'Psitticosaurus was Added.
'Caudipteryx was Added.
'Compsognathus was Added.
'Muttaburrasaurus was Added.
'
'Psitticosaurus
'Caudipteryx
'Compsognathus
'Muttaburrasaurus
'
'IndexOf("Muttaburrasaurus"): 3
'
'Contains("Caudipteryx"): True
'
'Insert(2, "Nanotyrannus")
'Nanotyrannus was Added.
'
'dinosaurs(2): Nanotyrannus
'
'dinosaurs(2) = "Microraptor"
'Nanotyrannus was replaced with Microraptor
'
'Remove("Microraptor")
'Microraptor was Removed.
'
'RemoveAt(0)
'Psitticosaurus was Removed.
'
'Caudipteryx
'Compsognathus
'Muttaburrasaurus

注釈

Count はゼロに設定され、コレクションの要素から他のオブジェクトへの参照も解放されます。

このメソッドは O(n) 操作です。nは Count です。

注意 (継承者)

派生クラスは、このメソッドをオーバーライドして、 メソッドの動作を Clear() 変更できます。

適用対象

こちらもご覧ください

• Clear()