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

  @override
  Widget 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

  @override
  Widget build(BuildContext context) {
      return MaterialApp(
          title: 'open url',body: Align(
              alignment: FractionalOffset(0.5,child: Text("chenyu"),);
  }
}

 

 

 

 

 

 

 

 

 

 

 

4、运行效果

测试1结果

项目结构如下

 

 

测试2结果