PointerSignalResolver

sample.packages.flutter.lib.src.gestures.pointer_signal_resolver.40.

Here is an example that demonstrates the effect of not using the resolver versus using it.

When this example is set to not use the resolver, then triggering the mouse wheel over the outer box will cause only the outer box to change color, but triggering the mouse wheel over the inner box will cause both the outer and the inner boxes to change color (because they're both receiving the event).

When this example is set to use the resolver, then only the box located directly under the cursor will change color when the mouse wheel is triggered.

  
import 'package:flutter/gestures.dart';

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      title: _title,
      home: MyStatefulWidget(),
    );
  }
}

class ColorChanger extends StatefulWidget {
  const ColorChanger({
    Key? key,
    required this.initialColor,
    required this.useResolver,
    this.child,
  }) : super(key: key);

  final HSVColor initialColor;
  final bool useResolver;
  final Widget? child;

  @override
  State createState() => _ColorChangerState();
}

class _ColorChangerState extends State {
  late HSVColor color;

  void rotateColor() {
    setState(() {
      color = color.withHue((color.hue + 3) % 360.0);
    });
  }

  @override
  void initState() {
    super.initState();
    color = widget.initialColor;
  }

  @override
  Widget build(BuildContext context) {
    return DecoratedBox(
      decoration: BoxDecoration(
        border: const Border.fromBorderSide(BorderSide()),
        color: color.toColor(),
      ),
      child: Listener(
        onPointerSignal: (PointerSignalEvent event) {
          if (widget.useResolver) {
            GestureBinding.instance.pointerSignalResolver.register(event,
                (PointerSignalEvent event) {
              rotateColor();
            });
          } else {
            rotateColor();
          }
        },
        child: Stack(
          fit: StackFit.expand,
          children: [
            const AbsorbPointer(),
            if (widget.child != null) widget.child!,
          ],
        ),
      ),
    );
  }
}

class MyStatefulWidget extends StatefulWidget {
  const MyStatefulWidget({Key? key}) : super(key: key);

  @override
  State createState() => _MyStatefulWidgetState();
}

class _MyStatefulWidgetState extends State {
  bool useResolver = false;

  @override
  Widget build(BuildContext context) {
    return Material(
      child: Stack(
        fit: StackFit.expand,
        children: [
          ColorChanger(
            initialColor: const HSVColor.fromAHSV(0.2, 120.0, 1, 1),
            useResolver: useResolver,
            child: FractionallySizedBox(
              widthFactor: 0.5,
              heightFactor: 0.5,
              child: ColorChanger(
                initialColor: const HSVColor.fromAHSV(1, 60.0, 1, 1),
                useResolver: useResolver,
              ),
            ),
          ),
          Align(
            alignment: Alignment.topLeft,
            child: Row(
              children: [
                Switch(
                  value: useResolver,
                  onChanged: (bool value) {
                    setState(() {
                      useResolver = value;
                    });
                  },
                ),
                const Text(
                  'Use the PointerSignalResolver?',
                  style: TextStyle(fontWeight: FontWeight.bold),
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }
}