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:
  

  private string firstname = string.Empty;
  
          public string FristName
          {
              get { return firstname; }
              set
              {
                  firstname = value;
  
              }
   }

• Add the same property into two controls as in the following:
  

  <TextBlock Margin="2">First Name</TextBlock>
  <TextBox Margin="2" Grid.Row="0" Grid.Column="1" MinWidth="120" Text="{Binding Path=FristName,ElementName=ThisControl,UpdateSourceTrigger=PropertyChanged}"></TextBox>
  <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.
  

  public partial class INotify : UserControl, INotifyPropertyChanged
  
   public INotify()
   {
       InitializeComponent();
   }
  
   private string firstname = string.Empty;
  
   public string FristName
   {
       get { return firstname; }
       set
       {
           firstname = value;
           OnPropertyChanged("FristName");
       }
   }
  
  
   #region INotifyPropertyChanged Members
  
   public event PropertyChangedEventHandler PropertyChanged;
   public void OnPropertyChanged(string txt)
   {
  
       PropertyChangedEventHandler handle = PropertyChanged;
       if (handle != null)
       {
           handle(this, new PropertyChangedEventArgs(txt));
       }
   }
   #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.