我尝试添加一个无法覆盖整个屏幕的 PageView

为此,我将PageView放在 Column 内:

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(),
      body: new Column(
        children: <Widget>[
          new SizedBox(height: 100.0, child: new Center(child: new Text("sticky header"))),
          new Expanded(
            child: new PageView(
              children: <Widget>[
                new Container(
                  color: Colors.red,
                  child: new Padding(
                    padding: const EdgeInsets.all(50.0),
                    child: new _Painter(),
                  ),
                ),
                new Container(
                  color: Colors.green,
                  child: new Padding(
                    padding: const EdgeInsets.all(50.0),
                    child: new _Painter(),
                  ),
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }
}

到目前为止,该方法有效。

每个PageView都有一个 _Painter ,其中有一个 RenderBox 可以画一些东西。

这是我的问题:我使用 handleEvent 方法检测拖动事件,但y位置错误。您会看到绘制的线不在我触摸屏幕的位置(透明气泡)。

dart - 在Flutter中增加大小的PageView的正确方法是什么?-LMLPHP

我怎样才能解决这个问题?我必须自己计算正确的y位置吗?

您可以找到full source here

更新
globalToLocal修复了问题的一半,但是我仍然必须在计算中包括填充。有没有办法获得小部件的填充?
void _handleDragUpdate(DragUpdateDetails details) {
  final pos = globalToLocal(details.globalPosition);
  _currentPath?.lineTo(pos.dx + 50.0, pos.dy + 50.0);
  markNeedsPaint();
}

奖励积分

当我左右拖动PageView时,我的_PainterRenderBox会忘记绘制的线条。记住这条线的最佳地点在哪里?将它们存储在_Painter还是_MyHomePageState中?

最佳答案

您缺少的是相对于globalPositionlocalPosition转换为RenderBox。你可以像这样实现

// onDragUpdate with the Painting Context
RenderBox referenceBox = context.findRenderObject();
Offset localPosition = referenceBox.globalToLocal(details.globalPosition);
// then use the localPosition to draw

用例的用法示例,如here所示:
class _PainterRenderBox extends RenderBox {
  final _lines = new List<Path>();
  PanGestureRecognizer _drag;
  Path _currentPath;

  // variable to store padding
  Offset padding;

  _PainterRenderBox() {
    final GestureArenaTeam team = new GestureArenaTeam();
    _drag = new PanGestureRecognizer()
      ..team = team
      ..onStart = _handleDragStart
      ..onUpdate = _handleDragUpdate
      ..onEnd = _handleDragEnd;
  }

  @override
  bool get sizedByParent => true;

  @override
  bool hitTestSelf(Offset position) => true;

  @override
  handleEvent(PointerEvent event, BoxHitTestEntry entry) {
    assert(debugHandleEvent(event, entry));
    if (event is PointerDownEvent) {
      _drag.addPointer(event);
    }
  }

  @override
  paint(PaintingContext context, Offset offset) {
    final Canvas canvas = context.canvas;

    // update padding
    padding = offset;

    final Paint paintBorder = new Paint()
      ..strokeWidth = 1.0
      ..style = PaintingStyle.stroke
      ..color = Colors.white.withAlpha(128);
    canvas.drawRect(offset & size, paintBorder);

    final Paint paintPath = new Paint()
      ..strokeWidth = 5.0
      ..style = PaintingStyle.stroke
      ..color = Colors.white;
    _lines.forEach((path) {
      canvas.drawPath(path, paintPath);
    });
  }

  // check if the point lies inside drawable area
  bool _canDraw(Offset offset){
    return (padding & size).contains(offset);
  }

  void _handleDragStart(DragStartDetails details) {
    _currentPath = new Path();
    Offset point = globalToLocal(details.globalPosition); // convert globalPosition to localPosition
    point = padding + point; // add the padding to localPosition if any
    // check if point lies inside drawable area and then markNeedsPaint
    if(_canDraw(point)){
      _currentPath?.moveTo(point.dx, point.dy);
      _lines.add(_currentPath);
      markNeedsPaint();
    }
  }

  void _handleDragUpdate(DragUpdateDetails details) {
    Offset point = globalToLocal(details.globalPosition); // convert globalPosition to localPosition
    point = padding + point; // add the padding to localPosition if any
    // check if point lies inside drawable area and then markNeedsPaint
    if(_canDraw(point)){
      _currentPath?.lineTo(point.dx, point.dy);
      markNeedsPaint();
    }
  }

  void _handleDragEnd(DragEndDetails details) {
    _currentPath = null;
    markNeedsPaint();
  }
}

存在一个具有类似用例的问题,该问题使用户可以在屏幕上签名。希望可以帮助您了解如何跟踪路径。您可以看看here

希望有帮助!

关于dart - 在Flutter中增加大小的PageView的正确方法是什么?,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/49320015/

10-09 21:29