Forums | NoesisGUI

Posted: **07 Apr 2019, 03:18**

Hi,

I have a very simple UserControl on which I apply

MouseDown="OnMouseDownMyUserControl"

in the XAML, and in the ConnectEvent of my root code-behind:

if (eventName == "MouseDown" && handlerName == "OnMouseDownMyUserControl"){
   ((MyUserControl)source).MouseDown += OnMouseDownMyUserControl;
   return true;
 }

and then:

void OnMouseDownMyUserControl(object sender, MouseButtonEventArgs args)
{
   var _offset = args.GetPosition(sender as MyUserControl);
   Console.WriteLine($"X: {_offset.X} Y: {_offset.Y}");
}

I'm getting:

X: 4.591495E-41 Y: 1.277719E-21

However, when I handle the MouseDown event directly in the MyUserControl code, eg,

public class MyUserControl: UserControl
{
    public MyUserControl()
    {
        this.MouseDown += (s, e) => {
                var _offset = e.GetPosition(s as Blargh);
                Console.WriteLine($"X: {_offset.X} Y: {_offset.Y}");
            };
    }
}

It works as expected and I'm getting (for example)

X: 89 Y: 306

What am I doing wrong in the first example? Thanks!

Posted: **07 Apr 2019, 17:01**

I think I found the culprit. In the version that binds the event from ConnectEvent, the handling function is marked as async, and I was doing something similar to:

async void OnMouseDownMyUserControl(object sender, MouseButtonEventArgs args)
{
   await doSomeAsyncStuff();
   var _offset = args.GetPosition(sender as MyUserControl);
   Console.WriteLine($"From Window X: {_offset.X} Y: {_offset.Y}");
}

It seems that args (potentially) loses its state when we await inside the MouseDown event;

Posted: **07 Apr 2019, 17:53**

That's right, event handlers cannot be executed asynchronously.
Also remark that the View and its UI tree cannot be modified from a different thread than the one used to create it.

Forums | NoesisGUI

Getting mouse position in MouseDown event

Getting mouse position in MouseDown event

Re: Getting mouse position in MouseDown event

Re: Getting mouse position in MouseDown event