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

Just a small comment - when using normal events you have to do var control= e.Sender as TextBox;, but you're using Rx and lambdas so this is still in scope. Your where-clause can be written as .Where(e => this != null && !string.IsNullOrEmpty(this.Text)). — Enigmativity
– Enigmativity, Commented Feb 3, 2016 at 7:00
And why are you calling off to Control_TextChanged? That seems to be a backwards step. Just put the code in the .Subscribe rather than in Control_TextChanged. — Enigmativity
– Enigmativity, Commented Feb 3, 2016 at 7:01
@Enigmativity another small comment :) We don't know if Control_TextChanged is called from somewhere else in the code. Or if the function length is 1000 lines. Point being: I think the implicit function call is better — supertopi
– supertopi, Commented Feb 3, 2016 at 8:36
@supertopi - We just don't know anything about it other than it is external to the current method. I try to use lambdas to encapsulate the code as encapsulation is one of the OO tenets so all things considered equal it's probably a good idea. — Enigmativity
– Enigmativity, Commented Feb 3, 2016 at 8:38

Grisha · Accepted Answer · 2016-02-03 06:29:34Z

4

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.

answered Feb 3, 2016 at 6:29

Grisha

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ds-b · Accepted Answer · 2016-02-03 07:29:05Z

3

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));

answered Feb 3, 2016 at 7:29

ds-b

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Jens Meinecke · Accepted Answer · 2016-02-03 11:41:13Z

2

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));

     })

edited Feb 3, 2016 at 11:41

answered Feb 3, 2016 at 5:59

Jens Meinecke

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4 Comments

vishal Over a year ago

where I can use, control.invoke. Could you pls give an example?

Jens Meinecke Over a year ago

See updated code. Sorry if it's a bit messy. Doing this on my phone.

vishal Over a year ago

Ah the one you are saying is in Windows.Form. I am using WPF

Jens Meinecke Over a year ago

I've never used WPF, but apparently the equivalent is to call Dispatcher.Invoke() - I have changed the answer accordingly.

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