Flutter之Align

1、Align介绍

Align的作为一个参数，设置子child的对齐方式，比如居中，左上，右下等多个对齐方向

2、部分源码和功能

  const Align({Key key,this.alignment = Alignment.center,this.widthFactor,this.heightFactor,Widget child,}) : assert(alignment != null),assert(widthFactor == null || widthFactor >= 0.0),assert(heightFactor == null || heightFactor >= 0.0),super(key: key, child: child);

  /// The top left corner.static const Alignment topLeft = Alignment(-1.0, -1.0);/// The center point along the top edge.static const Alignment topCenter = Alignment(0.0, -1.0);/// The top right corner.static const Alignment topRight = Alignment(1.0, -1.0);/// The center point along the left edge.static const Alignment centerLeft = Alignment(-1.0, 0.0);/// The center point, both horizontally and vertically.static const Alignment center = Alignment(0.0, 0.0);/// The center point along the right edge.static const Alignment centerRight = Alignment(1.0, 0.0);/// The bottom left corner.static const Alignment bottomLeft = Alignment(-1.0, 1.0);/// The center point along the bottom edge.static const Alignment bottomCenter = Alignment(0.0, 1.0);/// The bottom right corner.static const Alignment bottomRight = Alignment(1.0, 1.0);

我们知道最左上角的坐标是Alignment(-1.0, -1.0),中心坐标是Alignment(0.0, 0.0);然后最右下角坐标是Alignment(1.0, 1.0);

FractionalOffset对其封装了大小范围是(0~1),FractionalOffset(0, 0)对于左上角，FractionalOffset(1, 1)对于右下角，FractionalOffset(0.5, 0.5)对于中间坐标

FractionalOffset(0.5, 0.5) == Alignment(0.0,0.0) == Alignment.center

3、测试代码

测试1

  @overrideWidget build(BuildContext context) {return MaterialApp(title: 'open url',home: Scaffold(appBar: AppBar(// Here we take the value from the MyHomePage object that was created by// the App.build method, and use it to set our appbar title.title: Text('hello flutter'),),body: Align(alignment: FractionalOffset(1, 0),child: Container(color: Colors.red,width: 100,height: 100,),),),);}

测试2

  @overrideWidget build(BuildContext context) {return MaterialApp(title: 'open url',home: Scaffold(appBar: AppBar(// Here we take the value from the MyHomePage object that was created by// the App.build method, and use it to set our appbar title.title: Text('hello flutter'),),body: Align(alignment: FractionalOffset(0.5, 0),child: Text("chenyu"),),),);}
}