Flutter: How can I prevent default behaviour on key press?

Question

I'm trying to intercept when a user presses the volume buttons to perform a specific action and prevent the default behaviour (volume changes).

This is the code I have so far:

RawKeyboard.instance.addListener(_keyboardListener);

void _keyboardListener(RawKeyEvent e) {
  if(e.runtimeType == RawKeyUpEvent) {
    RawKeyEventDataAndroid eA = e.data;
    if(eA.keyCode == 24) { //volume up key
      _goNextPage();
    }
    if(eA.keyCode == 25) { //volume down key
      _goPrevPage();
    }
  }
}

How would I go about preventing the volume from changing (and stopping the volume slider from appearing at the top)?

A Javascript analogous would be calling event.preventDefault() on the key event.

This seems to be a rather trivial matter, but I haven't been able to find any answers in the docs.

Thanks.

Solution

I've faced a similar problem and what to share how I solved it.

To stop the propagation we have to return true from onKey method of a FocusNode in the focus nodes tree. To achieve this I've wrapped my app body with FocusScope and Focus widgets like this:

MaterialApp(
      home: Scaffold(
          body: FocusScope(
              autofocus: true,
              child: Focus(
                  autofocus: true,
                  canRequestFocus: true,
                  onKey: (data, event) {
                    if (event.isKeyPressed(LogicalKeyboardKey.audioVolumeUp)) {
                      print("Volume up");
                      return true;
                    }
                    if (event
                        .isKeyPressed(LogicalKeyboardKey.audioVolumeDown)) {
                      print("Volume down");
                      return true;
                    }
                    return false;
                  },
                  child: Text(text: "Hallochen")))))