INotifyPropertyChanged Interface
Updated: January 2010
Notifies clients that a property value has changed.
Assembly: System (in System.dll)
The INotifyPropertyChanged interface is used to notify clients, typically binding clients, that a property value has changed.
For example, consider a Person object with a property called FirstName. To provide generic property-change notification, the Person type implements the INotifyPropertyChanged interface and raises a PropertyChanged event when FirstName is changed.
For change notification to occur in a binding between a bound client and a data source, your bound type should either:
Implement the INotifyPropertyChanged interface (preferred).
Provide a change event for each property of the bound type.
Do not do both.
The following code example demonstrates the how to implement the INotifyPropertyChanged interface. When you run this example, you will notice the bound DataGridView control reflects the change in the data source without requiring the binding to be reset.
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
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The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.