Flutter之Align

系统管理员 2021-09-24 15:50 330阅读 0赞

## 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',
              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"),
                ),
              ),
          );
      }
    }

## 4、运行效果 ##

测试1结果

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTEwNjg3MDI_size_16_color_FFFFFF_t_70][]

项目结构如下

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTEwNjg3MDI_size_16_color_FFFFFF_t_70 1][]

测试2结果

![20200907203941546.png][]

![20200907204023447.png][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTEwNjg3MDI_size_16_color_FFFFFF_t_70]: /images/20210923/2f284f41856948309b8623a9033df2d1.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTEwNjg3MDI_size_16_color_FFFFFF_t_70 1]: /images/20210923/5473b9d1fcfd4e639607ca66039eed9c.png
[20200907203941546.png]: /images/20210923/9cb59cbecde04aeaaf3cfb9dfafdac1a.png
[20200907204023447.png]: /images/20210923/97e61cd73a7f41eeb6cfc1ad460b2caa.png