Flutter PointerEvent vs OnTap, one works, the other doesn't

Question

I have a stack widget I am trying to create in which: 1. The user touches the widget button triggering a pointerDown event. 2. Pointer down causes a slider type widget to scale from 0 to 100% from behind the button 3. With finger still down, the user drags to select a value on the scale 4. The value is selected by releasing the finger from the screen i.e. pointerUp.

The widget works fine when I use onTap instead of pointerDown in step 1. But when I try to use a pointer down event, the _open method (that manages the scaleUp of the slider) isn't triggered.

I have followed this example almost exactly: https://fireship.io/lessons/flutter-radial-menu-staggered-animations/, but have tried to change the touch event on the floatingActionbuton like this:

  Transform.scale(
              scale: widget.scale.value,
              child: Listener(
                  onPointerDown: (PointerDownEvent event) {
                    print('pointer is down');
                    setState(() {
                      _open;
                    });
                  },
                  child: FloatingActionButton(child: Icon(Icons.blur_circular), onPressed: () {})),
            )

The print part detects and fires the event, but the _open method does not do anything and the menu part does not appear like in the tutorial link.

I am at a loss.

Solution

Since the button below the FloatingActionButton also has a listener, The Listener widget doesn't get's the PointerDown event. So to do that you have to change the behaviour to opaque so that both get the events.

Try Something like this:

Listener(
  behavior: HitTestBehavior.opaque,
  onPointerDown: (PointerDownEvent details){

  },
  child: ...,
)

Comments

[Gary Frewin]

Unfortunately this hasn't changed the outcome. The print statement is still firing, just like before, and the animation doesn't fire. :/

[Adnan karim]

Im guessing _open is a function. Try calling _open()

[Gary Frewin]

Damn, that was it. For onTap I was calling _open, but for onPointerDown I have to call _open()...