Flutter学习第十二课:弹性布局Flex和水平排列Row和垂直排列Column

Flutter学习第十二课:弹性布局Flex和水平排列Row和垂直排列Column

一:弹性布局(Flex
弹性布局允许子组件按照一定比例来分配父容器空间。弹性布局的概念在其它UI系统中也都存在,如H5中的弹性盒子布局,Android中的FlexboxLayout等。Flutter中的弹性布局主要通过Flex和Expanded来配合实现

 Flex({
    Key? key,
    required this.direction,//Axis.vertical,Axis.horizontal,/弹性布局的方向, Row默认为水平方向,Column默认为垂直方向
    this.mainAxisAlignment = MainAxisAlignment.start,//主轴排列方式
    this.mainAxisSize = MainAxisSize.max,
    this.crossAxisAlignment = CrossAxisAlignment.center,//交叉轴排列方式
    this.textDirection,//
    this.verticalDirection = VerticalDirection.down,//设置垂直方向上的子 Widget 的排列顺序,默认为 VerticalDirection.down
    this.textBaseline, // NO DEFAULT: we don't know what the text's baseline should be//设置文字对齐的基线类型
    this.clipBehavior = Clip.none,
    List<Widget> children = const <Widget>[],//子组件
  }) : assert(direction != null),
       assert(mainAxisAlignment != null),
       assert(mainAxisSize != null),
       assert(crossAxisAlignment != null),
       assert(verticalDirection != null),
       assert(crossAxisAlignment != CrossAxisAlignment.baseline || textBaseline != null, 'textBaseline is required if you specify the crossAxisAlignment with CrossAxisAlignment.baseline'),
       assert(clipBehavior != null),
       super(key: key, children: children);

1. direction
设置主轴方向,可设置的值为 Axis.horizontal 和 Axis.vertical,交叉轴与主轴方向垂直。
在Flutter中,Row组件和Column组件都继承自Flex组件
(1).Flex组件和Row、Column属性主要的区别就是多一个direction。
(2).当direction的值为Axis.horizontal的时候,则是Row。
(3).当direction的值为Axis.vertical的时候,则是Column
2. mainAxisAlignment:
设置子 Widget 沿着主轴方向的排列方式,默认 MainAxisAlignment.start,可设置的方式如下:
MainAxisAlignment.start:左对齐,默认值;
MainAxisAlignment.end:右对齐;
MainAxisAlignment.center:居中对齐;
MainAxisAlignment.spaceBetween:两端对齐;
MainAxisAlignment.spaceAround:每个 Widget 两侧的间隔相等,与屏幕边缘的间隔是其他 Widget 之间间隔的一半;
MainAxisAlignment.spaceEvently:平均分布各个 Widget,与屏幕边缘的间隔与其他 Widget 之间的间隔相等.
3. mainAxisSize
设置主轴的大小,默认 MainAxisSize.max,可设置的值如下:
MainAxisSize.max:主轴的大小是父容器的大小;
MainAxisSize.min:主轴的大小是其子 Widget 大小之和。
4. crossAxisAlignment
设置子 Widget 沿着交叉轴方向的排列方式,默认 CrossAxisAlignment.center,可设置的方式如下:
CrossAxisAlignment.start:与交叉轴的起始位置对齐;
CrossAxisAlignment.end:与交叉轴的结束位置对齐;
CrossAxisAlignment.center:居中对齐;
CrossAxisAlignment.stretch:填充整个交叉轴;
CrossAxisAlignment.baseline:按照第一行文字基线对齐。
5. verticalDirection
设置垂直方向上的子 Widget 的排列顺序,默认为 VerticalDirection.down,设置方式如下:
VerticalDirection.down:start 在顶部,end 在底部;
VerticalDirection.up:start 在底部,end 在顶部。
6. textBaseline
设置文字对齐的基线类型,可设置的值如下:
TextBaseline.alphabetic:与字母基线对齐;
TextBaseline.ideographic:与表意字符基线对齐;

栗子:

 return Scaffold(
      body: Center(
        child: Flex(
          direction: Axis.vertical,////弹性布局的方向, Row默认为水平方向,Column默认为垂直方向
          mainAxisAlignment: MainAxisAlignment.spaceBetween,//主轴两端对齐
          mainAxisSize: MainAxisSize.max,//父类容器大小
          crossAxisAlignment: CrossAxisAlignment.center,//交叉轴居中对齐
          children: [
            Container(
              width: 200,
              height: 20,
              color: Colors.purple,
              child: Text('我是第一列'),
            ),
            Container(
              width: 150,
              height: 20,
              color: Colors.orange,
              child: Text('我是第二列'),
            ),
            Container(
              width: 100,
              height: 20,
              color: Colors.red,
              child: Text('我是第三列'),
            )
          ],

        ),

      ),

    );

二:Flutter组件之Row水平排列

//水平排列
Row({
    Key? key,
    MainAxisAlignment mainAxisAlignment = MainAxisAlignment.start,
    MainAxisSize mainAxisSize = MainAxisSize.max,
    CrossAxisAlignment crossAxisAlignment = CrossAxisAlignment.center,
    TextDirection? textDirection,
    VerticalDirection verticalDirection = VerticalDirection.down,
    TextBaseline? textBaseline, // NO DEFAULT: we don't know what the text's baseline should be
    List<Widget> children = const <Widget>[],
  }) : super(
    children: children,
    key: key,
    direction: Axis.horizontal,
    mainAxisAlignment: mainAxisAlignment,
    mainAxisSize: mainAxisSize,
    crossAxisAlignment: crossAxisAlignment,
    textDirection: textDirection,
    verticalDirection: verticalDirection,
    textBaseline: textBaseline,
  );


栗子:

return Scaffold(
      body: Center(
        child: Row(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,//主轴两端对齐
          mainAxisSize: MainAxisSize.max,//父类容器大小
          crossAxisAlignment: CrossAxisAlignment.center,//交叉轴居中对齐
          children: [
            Container(
              width: 100,
              height: 100,
              color: Colors.purple,
              child: Text('我是第一行'),
            ),
            Container(
              width: 100,
              height: 50,
              color: Colors.orange,
              child: Text('我是第二行'),
            ),
            Container(
              width: 100,
              height: 30,
              color: Colors.red,
              child: Text('我是第三行'),
            )
          ],

        ),

      ),

    );


三:Flutter组件之垂直排列Column

 Column({
    Key? key,
    MainAxisAlignment mainAxisAlignment = MainAxisAlignment.start,
    MainAxisSize mainAxisSize = MainAxisSize.max,
    CrossAxisAlignment crossAxisAlignment = CrossAxisAlignment.center,
    TextDirection? textDirection,
    VerticalDirection verticalDirection = VerticalDirection.down,
    TextBaseline? textBaseline,
    List<Widget> children = const <Widget>[],
  }) : super(
    children: children,
    key: key,
    direction: Axis.vertical,
    mainAxisAlignment: mainAxisAlignment,
    mainAxisSize: mainAxisSize,
    crossAxisAlignment: crossAxisAlignment,
    textDirection: textDirection,
    verticalDirection: verticalDirection,
    textBaseline: textBaseline,
  );

栗子:

return Scaffold(
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,//主轴两端对齐
          mainAxisSize: MainAxisSize.max,//父类容器大小
          crossAxisAlignment: CrossAxisAlignment.start,//交叉轴居中对齐
          children: [
            Container(
              width: 150,
              height: 100,
              color: Colors.purple,
              child: Text('我是第一Column列'),
            ),
            Container(
              width: 100,
              height: 50,
              color: Colors.orange,
              child: Text('我是第二Column列'),
            ),
            Container(
              width: 200,
              height: 30,
              color: Colors.red,
              child: Text('我是第三Column列'),
            )
          ],

        ),

      ),

    );

作者:Rocky_ruan 原文地址:https://segmentfault.com/a/1190000042537743

%s 个评论

要回复文章请先登录注册