dart – 如何使用颤动在按钮网格中滑动/拖动2个或更多按钮

例如,我们可以在按钮上方添加以下renderobject：

class Foo extends SingleChildRenderObjectWidget {
  final int index;

  Foo({Widget child,this.index,Key key}) : super(child: child,key: key);

  @override
  RenderObject createRenderObject(BuildContext context) {
    return _Foo()..index = index;
  }

  @override
  void updateRenderObject(BuildContext context,_Foo renderObject) {
    renderObject..index = index;
  }
}

class _Foo extends RenderProxyBox {
  int index;
}

然后使用Listener提取指针下找到的所有_Foo.

这是使用此原则的完整应用程序：

import 'package:flutter/gestures.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',theme: ThemeData(primarySwatch: Colors.blue),home: MyHomePage(title: 'Flutter Demo Home Page'),);
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key,this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),),body: Grid(),);
  }
}

class Grid extends StatefulWidget {
  @override
  GridState createState() {
    return new GridState();
  }
}

class GridState extends State<Grid> {
  final Set<int> selectedIndexes = Set<int>();
  final key = GlobalKey();
  final Set<_Foo> _trackTaped = Set<_Foo>();

  _detectTapedItem(PointerEvent event) {
    final RenderBox box = key.currentContext.findRenderObject();
    final result = HitTestResult();
    Offset local = box.globalToLocal(event.position);
    if (box.hitTest(result,position: local)) {
      for (final hit in result.path) {
        /// temporary variable so that the [is] allows access of [index]
        final target = hit.target;
        if (target is _Foo && !_trackTaped.contains(target)) {
          _trackTaped.add(target);
          _selectIndex(target.index);
        }
      }
    }
  }

  _selectIndex(int index) {
    setState(() {
      selectedIndexes.add(index);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Listener(
      onPointerDown: _detectTapedItem,onPointerMove: _detectTapedItem,onPointerUp: _clearSelection,child: GridView.builder(
        key: key,itemCount: 6,physics: NeverScrollableScrollPhysics(),gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(
          crossAxisCount: 3,childAspectRatio: 1.0,crossAxisSpacing: 5.0,mainAxisSpacing: 5.0,itemBuilder: (context,index) {
          return Foo(
            index: index,child: Container(
              color: selectedIndexes.contains(index) ? Colors.red : Colors.blue,);
        },);
  }

  void _clearSelection(PointerUpEvent event) {
    _trackTaped.clear();
    setState(() {
      selectedIndexes.clear();
    });
  }
}

class Foo extends SingleChildRenderObjectWidget {
  final int index;

  Foo({Widget child,key: key);

  @override
  _Foo createRenderObject(BuildContext context) {
    return _Foo()..index = index;
  }

  @override
  void updateRenderObject(BuildContext context,_Foo renderObject) {
    renderObject..index = index;
  }
}

class _Foo extends RenderProxyBox {
  int index;
}