How to: Implement Property Change Notification

To support OneWay or TwoWay binding to enable your binding target properties to automatically reflect the dynamic changes of the binding source (for example, to have the preview pane updated automatically when the user edits a form), your class needs to provide the proper property changed notifications. This example shows how to create a class that implements INotifyPropertyChanged.

Example

To implement INotifyPropertyChanged you need to declare the PropertyChanged event and create the OnPropertyChanged method. Then for each property you want change notifications for, you call OnPropertyChanged whenever the property is updated.

Imports System.ComponentModel
' This class implements INotifyPropertyChanged
' to support one-way and two-way bindings
' (such that the UI element updates when the source
' has been changed dynamically)
Public Class Person
 Implements INotifyPropertyChanged
 Private personName As String
 Sub New()
 End Sub
 Sub New(ByVal Name As String)
 Me.personName = Name
 End Sub
 ' Declare the event
 Public Event PropertyChanged As PropertyChangedEventHandler Implements INotifyPropertyChanged.PropertyChanged
 Public Property Name() As String
 Get
 Return personName
 End Get
 Set(ByVal value As String)
 personName = value
 ' Call OnPropertyChanged whenever the property is updated
 OnPropertyChanged("Name")
 End Set
 End Property
 ' Create the OnPropertyChanged method to raise the event
 Protected Sub OnPropertyChanged(ByVal name As String)
 RaiseEvent PropertyChanged(Me, New PropertyChangedEventArgs(name))
 End Sub
End Class

using System.ComponentModel;
namespace SDKSample
{
 // This class implements INotifyPropertyChanged
 // to support one-way and two-way bindings
 // (such that the UI element updates when the source
 // has been changed dynamically)
 public class Person : INotifyPropertyChanged
 {
 private string name;
 // Declare the event
 public event PropertyChangedEventHandler PropertyChanged;
 public Person()
 {
 }
 public Person(string value)
 {
 this.name = value;
 }
 public string PersonName
 {
 get { return name; }
 set
 {
 name = value;
 // Call OnPropertyChanged whenever the property is updated
 OnPropertyChanged("PersonName");
 }
 }
 // Create the OnPropertyChanged method to raise the event
 protected void OnPropertyChanged(string name)
 {
 PropertyChangedEventHandler handler = PropertyChanged;
 if (handler != null)
 {
 handler(this, new PropertyChangedEventArgs(name));
 }
 }
 }
}

To see an example of how the Person class can be used to support TwoWay binding, see How to: Control When the TextBox Text Updates the Source.

See Also

Concepts

Binding Sources Overview

Data Binding Overview

Other Resources

Data Binding How-to Topics