flutter : Change size of stack when children overflow

Question

我有一个可拖动的小部件(来自 https://medium.com/flutter-community/create-a-draggable-widget-in-flutter-50b61f12635d )，容器中的堆栈(红色)由可移动的子项组成。这是小部件树:

我想添加一个手势转换作为 FormBuilder ( https://github.com/flutter/flutter/blob/master/examples/flutter_gallery/lib/demo/transformations/transformations_demo.dart ) 来转换矩阵，正如你在 GIF 中看到的那样，主要是放大/缩小和转换 x/y。

class _HomeViewState extends State<HomeView> {
  final _stackKey;
  _HomeViewState(this._stackKey);
  List<Widget> movableItems = [];

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: AppBar(
        title: Text('SynApp'),
        actions: <Widget>[
          IconButton(
            onPressed: () {
              x = 200.0;
              y = 200.0;
              setState(() {
                movableItems.add(
                  MoveableStackItem(_stackKey),
                );
              });
            },
            icon: Icon(Icons.add),
          ),
        ],
      ),
      body: LayoutBuilder(
          builder: (BuildContext context, BoxConstraints constraints) {
        // Draw the scene as big as is available, but allow the user to
        // translate beyond that to a visibleSize that's a bit bigger.
        final Size size = Size(constraints.maxWidth, constraints.maxHeight);
        final Size visibleSize = Size(size.width * 3, size.height * 2);
        return GestureTransformable(
          reset: _reset,

          onResetEnd: () {
            setState(() {
              _reset = false;
            });
          },
          child: new Container(
            color: Colors.red,
            child: Stack(
                key: _stackKey,
                overflow: Overflow.visible,
                fit: StackFit.expand,
                children: movableItems),
          ),


          boundaryRect: Rect.fromLTWH(
            -visibleSize.width / 2,
            -visibleSize.height / 2,
            visibleSize.width,
            visibleSize.height,
          ),

          initialTranslation: Offset(size.width, size.height),
          size: size,
        );
      }),
    );
  }
}

问题是:

a) 堆栈的大小等于初始屏幕。

b)当我将项目移出屏幕时，手势检测停止，项目不再可移动。

我想要什么:我想根据我移动项目的位置动态调整堆栈(红色框)的大小。

我能够找到堆栈小部件的位置和大小。

  Size stackSize;
  Offset stackPosition;
  _MoveableStackItemState(this._stackKey);


  getSizeAndPosition() {
    RenderStack _stackStack = _stackKey.currentContext.findRenderObject();
    stackSize = _stackStack.size;
    stackPosition = _stackStack.localToGlobal(Offset.zero);
    print('stackSize $stackSize');
    print('stackPosition $stackPosition');
  }

但是我开始迷失在面向高级 UI 对象的有状态小部件操作中。

Answer 1

您可以使用 AnimatedContainer 包裹红色堆栈。

LayoutBuilder(
          builder: (BuildContext context, BoxConstraints constraints) {
        // Draw the scene as big as is available, but allow the user to
        // translate beyond that to a visibleSize that's a bit bigger.
        final Size size = Size(constraints.maxWidth, constraints.maxHeight);
        final Size visibleSize = Size(size.width * 3, size.height * 2);
        return GestureTransformable(
          reset: _reset,

          onResetEnd: () {
            setState(() {
              _reset = false;
            });
          },
          child: new AnimatedContainer(
            color: Colors.red,
            duration: Duration(milliseconds: 200),
            width: _stackWidth,
            height: _stackHeight,
            child: Stack(
                key: _stackKey,
                overflow: Overflow.visible,
                fit: StackFit.expand,
                children: movableItems),
          ),


          boundaryRect: Rect.fromLTWH(
            -visibleSize.width / 2,
            -visibleSize.height / 2,
            visibleSize.width,
            visibleSize.height,
          ),

          initialTranslation: Offset(size.width, size.height),
          size: size,
        );
      }),

尝试监听GestureTransformable的以下事件

onPanUpdate: (DragUpdateDetails details){
  var deltaX = details.delta.dx;
  var deltaY = details.delta.dy;
}

DragUpdateDetails 对象让您了解增量

the amount the pointer has moved in the coordinate space of the event receiver since the previous update

在 x 和 y 轴上。

在“onPanUpdate”中，您可以更新与手势增量相关的动画容器的宽度和高度。

setState((){
  _stackHeight = /* ... */
  _stackWidth = /* ... */
});