ConstraintCollection.CollectionChanged イベントとは何？わかりやすく解説 Weblio辞書

.NET Framework クラスライブラリリファレンス

索引トップ用語の索引ランキング

ConstraintCollection.CollectionChanged イベント

Constraint オブジェクトを追加または削除したことが原因で ConstraintCollection が変更されると、常に発生します。

名前空間: System.Data
アセンブリ: System.Data (system.data.dll 内)
構文

Visual Basic (宣言)

Public Event CollectionChanged As
 CollectionChangeEventHandler

Visual Basic (使用法)

Dim instance As ConstraintCollection
Dim handler As CollectionChangeEventHandler

AddHandler instance.CollectionChanged, handler

public event CollectionChangeEventHandler CollectionChanged

C++

public:
event CollectionChangeEventHandler^ CollectionChanged {
    void add (CollectionChangeEventHandler^ value);
    void remove (CollectionChangeEventHandler^ value);
}

/** @event */
public void add_CollectionChanged (CollectionChangeEventHandler
 value)

/** @event */
public void remove_CollectionChanged (CollectionChangeEventHandler
 value)

JScript

JScript では、イベントは使用できますが、新規に宣言することはできません。

解説

イベント処理の詳細については、「イベントの利用」を参照してください。

使用例

CollectionChanged イベントを使用する方法の例を次に示します。

Visual Basic

Private Shared Sub ConstraintCollectionChanged()
    ' Demonstrate ConstraintCollection.CollectionChanged event.
    Try
        ' Create Customers table.
        Dim customersTable As DataTable = New
 DataTable("Customers")
        customersTable.Columns.Add("id", Type.GetType("System.Int32"))
        customersTable.Columns.Add("Name", Type.GetType("System.String"))
        AddHandler customersTable.Constraints.CollectionChanged,
 _ 
            New System.ComponentModel.CollectionChangeEventHandler(
 _
            AddressOf Collection_Changed)

        ' Create Orders table.
        Dim ordersTable As DataTable = New
 DataTable("Orders")
        ordersTable.Columns.Add("CustID", Type.GetType("System.Int32"))
        ordersTable.Columns.Add("CustName", Type.GetType("System.String"))
        AddHandler ordersTable.Constraints.CollectionChanged,
 _
            New System.ComponentModel.CollectionChangeEventHandler(
 _
            AddressOf Collection_Changed)

        ' Create unique constraint.
        Dim constraint As UniqueConstraint
 = New _
            UniqueConstraint(customersTable.Columns("id"))
        customersTable.Constraints.Add(constraint)
        
        ' Create unique constraint and specify as primary key.
        ordersTable.Constraints.Add( _
            "pKey", ordersTable.Columns("CustID"),
 True)

        ' Remove constraints.
        customersTable.Constraints.RemoveAt( 0)

        ' Results in an Exception. You can't remove 
        ' a primary key constraint.
        ordersTable.Constraints.RemoveAt( 0) 
 
    Catch ex As Exception
        ' Process exception and return.
        Console.WriteLine("Exception of type {0} occurred.",
 _
            ex.GetType().ToString())
    End Try
End Sub

Private Shared Sub Collection_Changed(
 sender As object, _
    ex As System.ComponentModel.CollectionChangeEventArgs)
    Console.WriteLine("List_Changed Event: '{0}'\t
 element={1}", _
        ex.Action, ex.Element)
End Sub

private static void ConstraintCollectionChanged()
{
    // Demonstrate ConstraintCollection.CollectionChanged event.
    try
    {
        // Create Customers table.
        DataTable customersTable = new DataTable("Customers");
        customersTable.Columns.Add("id", typeof(int));
        customersTable.Columns.Add("Name", typeof(string));
        customersTable.Constraints.CollectionChanged += 
            new System.ComponentModel.CollectionChangeEventHandler(
 
            Collection_Changed);

        // Create Orders table.
        DataTable ordersTable = new DataTable("Orders");
        ordersTable.Columns.Add("CustID", typeof(int));
        ordersTable.Columns.Add("CustName", typeof(string));
        ordersTable.Constraints.CollectionChanged += 
            new System.ComponentModel.CollectionChangeEventHandler(
            Collection_Changed);

        // Create unique constraint.
        UniqueConstraint constraint = new UniqueConstraint(
            customersTable.Columns["id"]);
        customersTable.Constraints.Add(constraint);
    
        // Create unique constraint and specify as primary key.
        ordersTable.Constraints.Add(
            "pKey", ordersTable.Columns["CustID"], true);

        // Remove constraints.
        customersTable.Constraints.RemoveAt(0);

        // Results in an Exception. You can't remove 
        // a primary key constraint.
        ordersTable.Constraints.RemoveAt(0);  
    }
    catch(Exception ex)
    {
        // Process exception and return.
        Console.WriteLine("Exception of type {0} occurred.", 
            ex.GetType());
    }
}

private static void Collection_Changed(object
 sender, 
    System.ComponentModel.CollectionChangeEventArgs ex)
{
    Console.WriteLine("List_Changed Event: '{0}'\t element={1}", 
        ex.Action, ex.Element);
}