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.

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
            Return personName
        End Get
        Set(ByVal value As String)
            personName = value
            ' Call OnPropertyChanged whenever the property is updated
        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

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

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