Flutter：使用网格拖放

Question

我想创建一个小部件，您可以在其中添加多个不同大小的小部件，并可以使用拖放技术来更改其位置。类似于带有拖放功能的网格视图，您可以在其中水平和垂直更改位置。拖动选定的窗口小部件时，其他窗口小部件将四处移动以为其打开空间。

有没有人建议从哪里开始，或者已经有一些例子可以实现我所寻找的东西？

Answer 1

你也可以试试这个更简单的（不包括反馈）

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(home: Scaffold(body: HomePage()));
  }
}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  Offset offset = Offset.zero;

  @override
  Widget build(BuildContext context) {
    return Stack(
      children: <Widget>[
        Positioned(
          left: offset.dx,
          top: offset.dy,
          child: GestureDetector(
            onPanUpdate: (details) {
              setState(() {
                offset = Offset(offset.dx + details.delta.dx, offset.dy + details.delta.dy);
              });
            },
            child: Container(width: 100, height: 100, color: Colors.blue),
          ),
        ),
      ],
    );
  }
}

Answer 2

我创建了一个名为reorderables的包来解决这个问题。你只需要告诉包你的函数在拖放完成时被调用onReorder(int oldIndex, int newIndex)。

此示例在网格中有 9 个图标小部件 - 屏幕截图：ReorderableWrap

class _WrapExampleState extends State<WrapExample> {
  final double _iconSize = 90;
  List<Widget> _tiles;

  @override
  void initState() {
    super.initState();
    _tiles = <Widget>[
      Icon(Icons.filter_1, key: ValueKey(1), size: _iconSize),
      Icon(Icons.filter_2, key: ValueKey(2), size: _iconSize),
      Icon(Icons.filter_3, key: ValueKey(3), size: _iconSize),
      Icon(Icons.filter_4, key: ValueKey(4), size: _iconSize),
      Icon(Icons.filter_5, key: ValueKey(5), size: _iconSize),
      Icon(Icons.filter_6, key: ValueKey(6), size: _iconSize),
      Icon(Icons.filter_7, key: ValueKey(7), size: _iconSize),
      Icon(Icons.filter_8, key: ValueKey(8), size: _iconSize),
      Icon(Icons.filter_9, key: ValueKey(9), size: _iconSize),
    ];
  }

  @override
  Widget build(BuildContext context) {
    void _onReorder(int oldIndex, int newIndex) {
      setState(() {
        Widget row = _tiles.removeAt(oldIndex);
        _tiles.insert(newIndex, row);
      });
    }

    return ReorderableWrap(
      spacing: 8.0,
      runSpacing: 4.0,
      padding: const EdgeInsets.all(8),
      children: _tiles,
      onReorder: _onReorder
    );
  }
}

如果要限制列数，可以使用名为的可选参数 maxMainAxisCount

Answer 3

尽管这可能无法回答您的问题，但是正在寻找简单的拖放小部件的人，但是这里是示例。

查看我的第二个答案以更简单的方式

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text("Drag app"),
        ),
        body: HomePage(),
      ),
    );
  }
}

class HomePage extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return _HomePageState();
  }
}

class _HomePageState extends State<HomePage> {
  double width = 100.0, height = 100.0;
  Offset position ;

  @override
  void initState() {
    super.initState();
    position = Offset(0.0, height - 20);
  }

  @override
  Widget build(BuildContext context) {
    return Stack(
      children: <Widget>[
        Positioned(
          left: position.dx,
          top: position.dy - height + 20,
          child: Draggable(
            child: Container(
              width: width,
              height: height,
              color: Colors.blue,
              child: Center(child: Text("Drag", style: Theme.of(context).textTheme.headline,),),
            ),
            feedback: Container(
              child: Center(
                child: Text("Drag", style: Theme.of(context).textTheme.headline,),),
              color: Colors.blue[300],
              width: width,
              height: height,
            ),
            onDraggableCanceled: (Velocity velocity, Offset offset){
              setState(() => position = offset);
            },
          ),
        ),
      ],
    );
  }
}

Answer 4

这是可拖动文本的示例

class DraggableText extends StatefulWidget {
  final Offset initialOffset;
  final String text;

  DraggableText(this.text, this.initialOffset);

  @override
  _DraggableTextState createState() => new _DraggableTextState();
}

class _DraggableTextState extends State<DraggableText> {
  Offset position = new Offset(0.0, 0.0);

  @override
  void initState() {
    super.initState();
    position = widget.initialOffset;
  }

  @override
  Widget build(BuildContext context) {
    final item = new LabelBox(size: new Size.square(100.0), label: widget.text);
    final avatar = new LabelBox(
      size: new Size.square(150.0), label: widget.text, opacity: 0.4);
    final draggable = new Draggable(
      data: widget.text,
      feedback: avatar,
      child: item,
      childWhenDragging: new Opacity(opacity: 0.0, child: item),
      onDraggableCanceled: (velocity, offset) {
        print('_DragBoxState.build -> offset ${offset}');
        setState(() => position = offset);
      });
    return new Positioned(
      left: position.dx, top: position.dy, child: draggable);
  }
}

您可以在此处查看完整示例和更高级的示例https://github.com/rxlabz/flutter_dropcity