Example file: animation_full_control.dart Fix

[rdcoder33]

For example file example >> lib >> animation_full_control.dart

Using SetState in initState cause the following error
setState() or markNeedsBuild() called when widget tree was locked.

I have added a WidgetsBinding.instance.addPostFrameCallback wrapper to fix it. It's tested and work fine on all platforms.

@override
  void initState() {
    _controller = AnimationController(vsync: this);
    WidgetsBinding.instance.addPostFrameCallback((_) => setState(() {
          _controller
            .addListener(() {
              setState(() {
                // Rebuild the widget at each frame to update the "progress" label.
              });
            });
        }));

    super.initState();
  }