How to make delay in calling textchanged event of textbox in wpf

Question

I have custom control inherited from Textbox.

I want to make delay in calling textchanged event.

 Observable.FromEventPattern<TextChangedEventHandler, TextChangedEventArgs>(
                handler => this.TextChanged += handler,
                handler => this.TextChanged -= handler
                ).Throttle(TimeSpan.FromMilliseconds(600))
                      .Where(e =>
                          {
                              var control= e.Sender as TextBox;
                              return control!= null && !string.IsNullOrEmpty(control.Text);
                          })

                      .Subscribe(x => Control_TextChanged(x.Sender, x.EventArgs));

Problem is it is giving error saying, cannot access Text property as current thread does not have access.

Can someone please advice?

Thanks, Vishal

Answer 1

You can use ObserveOnDispatcher extension method and have something like:

Observable.FromEventPattern<TextChangedEventHandler, TextChangedEventArgs>(
                    ev => TextChanged += ev,
                    ev => TextChanged -= ev)
                          .Where(t => !string.IsNullOrEmpty(Text))
                          .Throttle(TimeSpan.FromMilliseconds(600))
                          .ObserveOnDispatcher()
                          .Subscribe(e => HandleTextChanged(e.EventArgs));

Answer 2

You can observe on UI thread:

Observable.FromEventPattern<TextChangedEventHandler, TextChangedEventArgs>(
  handler => this.TextChanged += handler,
  handler => this.TextChanged -= handler)     
     .ObserveOn(DispatcherScheduler.Current)
     .Throttle(TimeSpan.FromMilliseconds(600))
     .Where(e =>
          {
              var control= e.Sender as TextBox;
              return control!= null && !string.IsNullOrEmpty(control.Text);
          })
     .Subscribe(x => Control_TextChanged(x.Sender, x.EventArgs));

Notice the use of DispatcherScheduler.Current it's in System.Reactive.Windows.Threading namespace in Rx-WPF NuGet package.

Answer 3

You will have to use Control.Invoke() to make changes to UI elements from any thread other than the main UI thread.

Where(e =>
    {
     var control= e.Sender as TextBox;

     return control != null 
          && !string.IsNullOrEmpty(Dispatcher.Invoke<string>(()=>  control.Text));

     })