touchmove, touchmove.prevent, touchstart events don't report X/Y coordinates for ui components

[aabrodskiy]

Description

While trying to implement mobile drag/drop behaviour, I ran into the fact that neither of touch events report ClientX/Y or pageX/Y into the GenericEventArguments structure, unlike the normal drag events.
Is this a simple bug that's easy to fix, or is it some sort of limitation of the framework?

[aabrodskiy]

By trial and error I found that "pointer" group of events produces all Xs and Ys while moving, so ended up implementing those handlers and it works just fine.

      .on('pointerdown', lambda e, c=col: self.handle_drag_start(e, c))\
      .on('pointerup', lambda e, c=col: self.handle_drop(e, c))\
      .on('pointermove.prevent', throttle=0.2, handler=lambda e: self.handle_pointer_move_prevent(e)):

in pointermove handler, it's important to check if it's indeed coming from the touch actions, or just normal mouse moving:

    async def handle_pointer_move_prevent(self, event):
        type = event.args.get('type')
        pointer_type = event.args.get('pointerType')
        if type == 'pointermove' and pointer_type == 'touch':
            #your logic goes here

[falkoschindler]

Hi @aabrodskiy,

I'm not aware of a specific limitation for touch event arguments. Maybe you can share your code so that we can try to reproduce the problem more easily?

You mention you're implementing a mobile interface. Maybe it's a limitation of Safari. They don't seem to support touch events: https://developer.mozilla.org/en-US/docs/Web/API/Touch_events#browser_compatibility. So maybe pointer events are the better option anyway.