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如何在垂直（高度）和水平（宽度）方向上实现窗口小部件的扩展

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下面的代码列出了一个图表，我需要在图表中实现图表在垂直（高度）和水平（宽度）方向上的扩展 . 建议的方法（例如https://docs.flutter.io/flutter/widgets/Row-class.html）是在 Row 或 Column 中使用 Expanded .

我试图扩展的图表小部件扩展 CustomPaint ，没有子节点，所有内容都在 CustomPainter.paint(canvas, size) 上使用 CustomPainter 在画布上绘制 .

这段代码

return new Scaffold(
  appBar: new AppBar(
    title: new Text(widget.title),
  ),
  body: new Center(    
    child: new Column(
      mainAxisAlignment: MainAxisAlignment.center,
      children: <Widget>[
        new Text(
          'vvvvvvvv:',
        ),
        new RaisedButton(
          color: Colors.green,
          onPressed: _chartStateChanger,
        ),
        new Text(
          'vvvvvvvv:',
        ),    
        new Expanded( // Expanded in Column, no expansion vertically 
          child: new Row(
            children: [
              new Text('>>>'),    
              new Expanded(// Expanded in Row, expands horizontally
                child: new Chart(  // extends CustomPaint
                  // size: chartLogicalSize,
                  painter: new ChartPainter( // extends CustomPainter
                    chartData: _chartData,
                    chartOptions: _chartOptions,
                  ),
                ),
              ),
              new Text('<<<'),
            ],
          ),  // row
        ),
        new Text('^^^^^^:'),
        new RaisedButton(
          color: Colors.green,
          onPressed: _chartStateChanger,
        ),
      ],
    ),
  ),
);

结果如下所示:(为简洁起见，未显示ChartPainter的代码）
result of the above code

在 ChartPainter.paint(canvas, size) 内部有一个 print() 打印尺寸 .

print（“### Size：paint（）：传递size = $ ”）;

上面的paint-> print的结果是：

I / flutter（4187）：###尺寸：paint（）：传递尺寸=尺寸（340.0,0.0）

打印与图像一起显示，行级别的宽度扩展已传递到 CustomPainter.print(canvas, size) （宽度= 340.0），但列上的高度扩展未传递到自定义画家打印（高度= 0.0） . 虽然结果显示行确实得到了它的扩展高度，但如果没有在行内传递到 CustomPainter - 0高度被接收 .

我还需要改变什么来实现高度扩展？

谢谢

flutter

2 回答

  • 1

    这是针对您所看到的问题的简化测试用例 . 解决方案是给你的 Row crossAxisAlignment CrossAxisAlignment.stretch . 否则它将尝试确定 CustomPaint 的内在高度，因为它没有孩子，所以它为零 .

    import 'package:flutter/material.dart';

// from https://stackoverflow.com/questions/45875334/how-to-achieve-expansion-of-a-widget-in-both-vertical-height-and-horizontal-w

class MyCustomPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    // NOT using crossAxisAlignment: CrossAxisAlignment.stretch => width = 222.0, height=0.0
    // using crossAxisAlignment: CrossAxisAlignment.stretch     => width = 222.0, height=560.0
    print("width = ${size.width}, height=${size.height}");
    canvas.drawRect(Offset.zero & size, new Paint()..color = Colors.blue);
  }

  @override
  bool shouldRepaint(MyCustomPainter other) => false;
}
void main() {
  runApp(new MaterialApp(
    home: new Scaffold(
        body: new Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            new Text('Above Paint'),
            // Expanded - because we are in Column, expand the
            //            contained row's height
            new Expanded(
              child: new Row(
                // The crossAxisAlignment is needed to give content height > 0
                //   - we are in a Row, so crossAxis is Column, so this enforces
                //     to "stretch height".
                crossAxisAlignment: CrossAxisAlignment.stretch,
                children: <Widget>[
                  new Text('Left of Paint'),
                  // Expanded - because we are in Row, expand the
                  //           contained Painter's width
                  new Expanded(
                    child: new CustomPaint(
                      painter: new MyCustomPainter(),
                    ),
                  ),
                  new Text('Right of Paint'),
                ],
              ),
            ),
            new Text('Below Paint'),
          ],
        )
    ),
  ));
}
    回复于
  • 11

    有一种比嵌套 Row ， Expended 和 Column 小部件更好的方法 . 您可以将 Container 小部件与 Constraints 一起使用到 BoxConstraints.expend() .

    这是我的小部件的代码捕捉 .

    Widget build(BuildContext context) {
      return Container(
        constraints: BoxConstraints.expand(), 
        child: FutureBuilder(
          future: loadImage(),
          builder: (BuildContext context, AsyncSnapshot<ui.Image> snapshot) {
            switch(snapshot.connectionState) {
              case ConnectionState.waiting : 
                return Center(child: Text("loading..."),);
              default:
                if (snapshot.hasError) {
                  return Center(child: Text("error: ${snapshot.error}"),);
                } else {
                  return ImagePainter(image: snapshot.data);
                }
              }
            },
          ),
      );
    }
    回复于

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