Dim lowerLayer when Rubber is active about rubber

[edisonywh]

@jonivesto thanks for the code example! I tried something similar but with addStatusListener, and it worked pretty bad because it's hard to know when the animation starts to drag up/down in order to rebuild. Haven't tried out your example yet but it's probably better than mine :)

For now I've actually just used the built in Flutter one, there was a new update recently to fix the slide up animation so that looks better now!

[jonivesto]

@edisonywh I agree, this is a must have feature in a plugin like this. In the meantime, you can use this solution:

1. Wrap your lowerLayer widget with Stack
2. Add a Container to your Stack and set it's color to black
3. Wrap the Container with Opacity
4. Wrap the Opacity with IgnorePointer

5, Now you can use addListener() to set states for the Opacity and IgnorePointer like this:

@override
  void initState() {
    _rubberController = RubberAnimationController(
      vsync: this,
      duration: Duration(milliseconds: 300),
      dismissable: true,     
    );
    _rubberController.addListener((){
      setState(() {
        _opacity = _rubberController.value;
        _ignoring = _rubberController.value<0.5;
      });
    });
    super.initState();
  }