Gewusst wie: Auslösen von Änderungsbenachrichtigungen mithilfe von "BindingSource" und der "INotifyPropertyChanged"-Schnittstelle
Die BindingSource-Komponente erkennt automatisch Änderungen in einer Datenquelle, wenn der in der Datenquelle enthaltene Typ die INotifyPropertyChanged-Schnittstelle implementiert und PropertyChanged-Ereignisse auslöst, sobald ein Eigenschaftswert geändert wird. Dies ist nützlich, da an die BindingSource gebundene Steuerelemente automatisch aktualisiert werden, wenn sich die Datenquellenwerte ändern.
Tipp
Wenn die Datenquelle INotifyPropertyChanged implementiert, sollten Sie beim Durchführen asynchroner Operationen keine Änderungen an der Datenquelle in einem Hintergrundthread vornehmen. Lesen Sie die Daten stattdessen in einem Hintergrundthread, und führen Sie sie in einer Liste auf dem UI-Thread zusammen.
Beispiel
Das folgende Codebeispiel veranschaulicht eine einfache Implementierung der INotifyPropertyChanged-Schnittstelle. Darüber hinaus wird gezeigt, wie BindingSource automatisch eine Datenquellenänderung an ein gebundenes Steuerelement übergibt, wenn BindingSource an eine Liste des INotifyPropertyChanged-Typs gebunden ist.
Imports System
Imports System.Collections.Generic
Imports System.ComponentModel
Imports System.Data
Imports System.Data.Common
Imports System.Diagnostics
Imports System.Drawing
Imports System.Data.SqlClient
Imports System.Windows.Forms
' This form demonstrates using a BindingSource to bind
' a list to a DataGridView control. The list does not
' raise change notifications, however the DemoCustomer type
' in the list does.
Public Class Form1
Inherits System.Windows.Forms.Form
' This button causes the value of a list element to be changed.
Private changeItemBtn As New Button()
' This DataGridView control displays the contents of the list.
Private customersDataGridView As New DataGridView()
' This BindingSource binds the list to the DataGridView control.
Private customersBindingSource As New BindingSource()
Public Sub New()
' Set up the "Change Item" button.
Me.changeItemBtn.Text = "Change Item"
Me.changeItemBtn.Dock = DockStyle.Bottom
AddHandler Me.changeItemBtn.Click, AddressOf changeItemBtn_Click
Me.Controls.Add(Me.changeItemBtn)
' Set up the DataGridView.
customersDataGridView.Dock = DockStyle.Top
Me.Controls.Add(customersDataGridView)
Me.Size = New Size(800, 200)
AddHandler Me.Load, AddressOf Form1_Load
End Sub 'New
Private Sub Form1_Load(ByVal sender As System.Object, _
ByVal e As System.EventArgs) Handles Me.Load
' Create and populate the list of DemoCustomer objects
' which will supply data to the DataGridView.
Dim customerList As New BindingList(Of DemoCustomer)
customerList.Add(DemoCustomer.CreateNewCustomer())
customerList.Add(DemoCustomer.CreateNewCustomer())
customerList.Add(DemoCustomer.CreateNewCustomer())
' Bind the list to the BindingSource.
Me.customersBindingSource.DataSource = customerList
' Attach the BindingSource to the DataGridView.
Me.customersDataGridView.DataSource = Me.customersBindingSource
End Sub 'Form1_Load
' This event handler changes the value of the CompanyName
' property for the first item in the list.
Private Sub changeItemBtn_Click(ByVal sender As Object, ByVal e As EventArgs)
' Get a reference to the list from the BindingSource.
Dim customerList As BindingList(Of DemoCustomer) = _
CType(customersBindingSource.DataSource, BindingList(Of DemoCustomer))
' Change the value of the CompanyName property for the
' first item in the list.
customerList(0).CustomerName = "Tailspin Toys"
End Sub
<STAThread()> _
Shared Sub Main()
Application.EnableVisualStyles()
Application.Run(New Form1())
End Sub
End Class
' This class implements a simple customer type
' that implements the IPropertyChange interface.
Public Class DemoCustomer
Implements INotifyPropertyChanged
' These fields hold the values for the public properties.
Private idValue As Guid = Guid.NewGuid()
Private customerNameValue As String = String.Empty
Private phoneNumberValue As String = String.Empty
Public Event PropertyChanged As PropertyChangedEventHandler _
Implements INotifyPropertyChanged.PropertyChanged
Private Sub NotifyPropertyChanged(ByVal info As String)
RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(info))
End Sub
' The constructor is private to enforce the factory pattern.
Private Sub New()
customerNameValue = "Customer"
phoneNumberValue = "(555)555-5555"
End Sub
' This is the public factory method.
Public Shared Function CreateNewCustomer() As DemoCustomer
Return New DemoCustomer()
End Function
' This property represents an ID, suitable
' for use as a primary key in a database.
Public ReadOnly Property ID() As Guid
Get
Return Me.idValue
End Get
End Property
Public Property CustomerName() As String
Get
Return Me.customerNameValue
End Get
Set(ByVal value As String)
If Not (value = customerNameValue) Then
Me.customerNameValue = value
NotifyPropertyChanged("CustomerName")
End If
End Set
End Property
Public Property PhoneNumber() As String
Get
Return Me.phoneNumberValue
End Get
Set(ByVal value As String)
If Not (value = phoneNumberValue) Then
Me.phoneNumberValue = value
NotifyPropertyChanged("PhoneNumber")
End If
End Set
End Property
End Class
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Data.Common;
using System.Diagnostics;
using System.Drawing;
using System.Data.SqlClient;
using System.Windows.Forms;
// This form demonstrates using a BindingSource to bind
// a list to a DataGridView control. The list does not
// raise change notifications, however the DemoCustomer type
// in the list does.
public class Form1 : System.Windows.Forms.Form
{
// This button causes the value of a list element to be changed.
private Button changeItemBtn = new Button();
// This DataGridView control displays the contents of the list.
private DataGridView customersDataGridView = new DataGridView();
// This BindingSource binds the list to the DataGridView control.
private BindingSource customersBindingSource = new BindingSource();
public Form1()
{
// Set up the "Change Item" button.
this.changeItemBtn.Text = "Change Item";
this.changeItemBtn.Dock = DockStyle.Bottom;
this.changeItemBtn.Click +=
new EventHandler(changeItemBtn_Click);
this.Controls.Add(this.changeItemBtn);
// Set up the DataGridView.
customersDataGridView.Dock = DockStyle.Top;
this.Controls.Add(customersDataGridView);
this.Size = new Size(800, 200);
this.Load += new EventHandler(Form1_Load);
}
private void Form1_Load(System.Object sender, System.EventArgs e)
{
// Create and populate the list of DemoCustomer objects
// which will supply data to the DataGridView.
BindingList<DemoCustomer> customerList = new BindingList<DemoCustomer>();
customerList.Add(DemoCustomer.CreateNewCustomer());
customerList.Add(DemoCustomer.CreateNewCustomer());
customerList.Add(DemoCustomer.CreateNewCustomer());
// Bind the list to the BindingSource.
this.customersBindingSource.DataSource = customerList;
// Attach the BindingSource to the DataGridView.
this.customersDataGridView.DataSource =
this.customersBindingSource;
}
// Change the value of the CompanyName property for the first
// item in the list when the "Change Item" button is clicked.
void changeItemBtn_Click(object sender, EventArgs e)
{
// Get a reference to the list from the BindingSource.
BindingList<DemoCustomer> customerList =
this.customersBindingSource.DataSource as BindingList<DemoCustomer>;
// Change the value of the CompanyName property for the
// first item in the list.
customerList[0].CustomerName = "Tailspin Toys";
}
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.Run(new Form1());
}
}
// This is a simple customer class that
// implements the IPropertyChange interface.
public class DemoCustomer : INotifyPropertyChanged
{
// These fields hold the values for the public properties.
private Guid idValue = Guid.NewGuid();
private string customerNameValue = String.Empty;
private string phoneNumberValue = String.Empty;
public event PropertyChangedEventHandler PropertyChanged;
private void NotifyPropertyChanged(String info)
{
if (PropertyChanged != null)
{
PropertyChanged(this, new PropertyChangedEventArgs(info));
}
}
// The constructor is private to enforce the factory pattern.
private DemoCustomer()
{
customerNameValue = "Customer";
phoneNumberValue = "(555)555-5555";
}
// This is the public factory method.
public static DemoCustomer CreateNewCustomer()
{
return new DemoCustomer();
}
// This property represents an ID, suitable
// for use as a primary key in a database.
public Guid ID
{
get
{
return this.idValue;
}
}
public string CustomerName
{
get
{
return this.customerNameValue;
}
set
{
if (value != this.customerNameValue)
{
this.customerNameValue = value;
NotifyPropertyChanged("CustomerName");
}
}
}
public string PhoneNumber
{
get
{
return this.phoneNumberValue;
}
set
{
if (value != this.phoneNumberValue)
{
this.phoneNumberValue = value;
NotifyPropertyChanged("PhoneNumber");
}
}
}
}
Kompilieren des Codes
Für dieses Beispiel sind erforderlich:
- Verweise auf die Assemblys System, System.Data, System.Drawing sowie System.Windows.Forms.
Informationen zum Erstellen dieses Beispiels über die Befehlszeile für Visual Basic oder Visual C# finden Sie unter Erstellen von der Befehlszeile aus (Visual Basic) und Erstellen über die Befehlszeile mit csc.exe. Sie können dieses Beispiel auch in Visual Studio erstellen, indem Sie den Code in ein neues Projekt einfügen. Weitere Informationen finden Sie unter Gewusst wie: Kompilieren und Ausführen eines vollständigen Windows Forms-Codebeispiels mit Visual Studio und Gewusst wie: Kompilieren und Ausführen eines vollständigen Windows Forms-Codebeispiels mit Visual Studio und Gewusst wie: Kompilieren und Ausführen eines vollständigen Windows Forms-Codebeispiels mit Visual Studio und Gewusst wie: Kompilieren und Ausführen eines vollständigen Windows Forms-Codebeispiels mit Visual Studio und Gewusst wie: Kompilieren und Ausführen eines vollständigen Windows Forms-Codebeispiels mit Visual Studio.