Implement Change Notification Using INotifyPropertyChanged in WPF

INotifyPropertyChanged was introduced in .NET 2.0. This interface has only one member, the PropertyChanged event that will notify listeners when a property of the implementing class is changed.

Demo

• Open Visual Studio and select WPF application.
  
• Open/add one user control or window.
  
• Create one normal property, here I have added FirstName as in the following:
  
  1. private string firstname = string.Empty;
  3. public string FristName
  4. {
  5. get { return firstname; }
  6. set
  7. {
  8. firstname = value;
  10. }
  11. }
• Add the same property into two controls as in the following:
  
  1. <TextBlock Margin="2">First Name</TextBlock>
  2. <TextBox Margin="2" Grid.Row="0" Grid.Column="1" MinWidth="120" Text="{Binding Path=FristName,ElementName=ThisControl,UpdateSourceTrigger=PropertyChanged}"></TextBox>
  3. <TextBlock Margin="2" Grid.Column="2" Text="{Binding Path=FristName,ElementName=ThisControl,UpdateSourceTrigger=PropertyChanged}"></TextBlock>
• Run the application, I entered the first name field but not displaying in my TextBlock in the right side.
  
  
  
  
  
  
• But we can see the property change in the preceding picture. But it's not reflecting it in the UI.
  
• Implement the INotifyPropertyChanged interface, no change in the XAML.
  
  1. public partial class INotify : UserControl, INotifyPropertyChanged
  3. public INotify()
  4. {
  5. InitializeComponent();
  6. }
  8. private string firstname = string.Empty;
  10. public string FristName
  11. {
  12. get { return firstname; }
  13. set
  14. {
  15. firstname = value;
  16. OnPropertyChanged("FristName");
  17. }
  18. }
  21. #region INotifyPropertyChanged Members
  23. public event PropertyChangedEventHandler PropertyChanged;
  24. public void OnPropertyChanged(string txt)
  25. {
  27. PropertyChangedEventHandler handle = PropertyChanged;
  28. if (handle != null)
  29. {
  30. handle(this, new PropertyChangedEventArgs(txt));
  31. }
  32. }
  33. #endregion
• Run the application and see the change.
  
  
  
• We got the change in the UI.

Conclusion

The INotifyPropertyChanged interface will notify the source of changes to the target.