Flutter -- 5.布局相关

• Flutter中，布局方式为弹性盒子布局
• 可以将一个一个Widget看做一个一个矩形盒子，盒子套盒子模式

1.Container

• 如果没有设置child，Container大小与上层一致
• 如果设置了child，大小与child大小一致
• alignment(x,y)，值范围从-1.0到1.0。设置子部件对齐方式。如果当前Container上层大小确定，设置alignment后，Container大小不受child大小影响
  • alignment(-1,-1)，左上角。等于Alignment.topLeft
  • alignment(0,0)，中间。等于Alignment.center
  • alignment(1,1),右下角。等于Alignment.bottomRight

class ContainerDemo extends StatelessWidget {
  const ContainerDemo({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {

    return Container(
      color: Colors.grey[400],
      child: Container(
        width: 200,
        height: 200,
        color: Colors.red,
      ),
      alignment: Alignment.center, //设置后，不受child影响
    );
  }
}

layout_container.png	layout_container_alignment.png

2.Flex

• Row、Column的父类
• 可以沿着水平或垂直方向排列子Widget
• direction，必填参数，排列方向

class FlexDemo extends StatelessWidget {
  const FlexDemo({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.grey[400],
      child: Flex(
        direction: Axis.horizontal,
        children: [
          Container(
            width: 60,
            color: Colors.red,
            child: const AspectRatio(aspectRatio: 1,),
          ),
          Container(
            width: 80,
            color: Colors.blue,
            child: const AspectRatio(aspectRatio: 1,),
          ),
          Container(
            width: 100,
            color: Colors.yellow,
            child: const AspectRatio(aspectRatio: 1,),
          ),
        ],
      ),
    );
  }
}

laout_flex_horizontal	laout_flex_vertical

3.主轴

• 类型为MainAxisAlignment
• 横向布局，默认方向为由左向右
• 纵向布局，默认方向为由上到下
• start - 主轴最开始地方，默认值
• center - 主轴中间地方
• end - 主轴结束地方
• spaceBottom - 小组件间的间距的平均分布
• spaceAround - 小组件间周围平均分布
• spaceEvenly - 小组件均匀分布

class FlexDemo extends StatelessWidget {
  const FlexDemo({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.grey[400],
      alignment: Alignment.center,
      child: Flex(
        mainAxisAlignment: MainAxisAlignment.spaceAround,
        direction: Axis.horizontal,
        children: [
          Container(
            width: 60,
            color: Colors.red,
            child: const AspectRatio(aspectRatio: 1,),
          ),
          Container(
            width: 80,
            color: Colors.blue,
            child: const AspectRatio(aspectRatio: 1,),
          ),
          Container(
            width: 100,
            color: Colors.yellow,
            child: const AspectRatio(aspectRatio: 1,),
          ),
        ],
      ),
    );
  }
}

flex_mainAxisAlignment_start.png	flex_mainAxisAlignment_center.png	flex_mainAxisAlignment_end.png
flex_mainAxisAlignment_spaceBetween.png	flex_mainAxisAlignment_spaceAround.png	flex_mainAxisAlignments_paceEvenly.png

4.交叉轴

• 类型为MainAxisAlignment
• start - 交叉轴最开始地方
• center - 交叉轴中间地方，默认值
• end - 交叉轴结束地方
• stretch - 交叉轴方向拉伸满
• spaceAround - 小组件间周围平均分布
• baseLIne - 基准线。当direction: Axis.horizontal时，多个小部件为Text时，基于文字对齐。英文alphabetic其他语言ideographic。注意这里只有设置了textBaseLine才能设置，否则会报错

class FlexBaselineDemo extends StatelessWidget {
  const FlexBaselineDemo({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.grey[400],
      alignment: Alignment.center,
      child: Flex(
        mainAxisAlignment: MainAxisAlignment.spaceEvenly,
        crossAxisAlignment: CrossAxisAlignment.baseline,
        /*
        * TextBaseLine
        * alphabetic，英文
        * ideographic，其他语言
        * 测试完感觉2者在中文/英文来用任意一个都差不多
        * */
        textBaseline: TextBaseline.ideographic, 
        direction: Axis.horizontal,
        children: [
          Container(
            width: 60,
            color: Colors.red,
            child: const AspectRatio(
              aspectRatio: 1,
              child: Center(
                child: Text("红色", style: TextStyle(fontSize: 15, color: Colors.white),),
              ),
            ),
          ),
          Container(
            width: 80,
            color: Colors.blue,
            child: const AspectRatio(
              aspectRatio: 1,
              child: Center(
                child: Text("蓝色", style: TextStyle(fontSize: 20, color: Colors.white),),
              ),
            ),
          ),
          Container(
            width: 100,
            color: Colors.yellow,
            child: const AspectRatio(
              aspectRatio: 1,
              child: Center(
                child: Text("黄色", style: TextStyle(fontSize: 30, color: Colors.white),),
              ),
            ),
          ),
        ],
      ),
    );
  }
}

flex_crossAxisAlignment_start.png	flex_crossAxisAlignment_center.png	flex_crossAxisAlignment_end.png
flex_crossAxisAlignment_stretch.png	flex_crossAxisAlignment_baseline_ideographic.png	flex_crossAxisAlignment_baseline_alphabetic.png

5.Row、Column

• Row、Column继承Flex
• Row相当于Flex中direction: Axis.horizontal
• Column相当于Flex中direction: Axis.vertical
• 使用方式与Flex一致
• 注意：textDirection设置后可以改变主轴方向，仅在Row上改变主轴方向

class RowOrColumnDemo extends StatelessWidget {

  final bool isRow;
  
  const RowOrColumnDemo(this.isRow);

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.grey[400],
      alignment: Alignment.center,
      child: isRow ? Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Container(
            width: 60,
            color: Colors.red,
            child: const AspectRatio(aspectRatio: 1,),
          ),
          Container(
            width: 80,
            color: Colors.blue,
            child: const AspectRatio(aspectRatio: 1,),
          ),
          Container(
            width: 100,
            color: Colors.yellow,
            child: const AspectRatio(aspectRatio: 1,),
          ),
        ],
      ) :
      Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Container(
            width: 60,
            color: Colors.red,
            child: const AspectRatio(aspectRatio: 1,),
          ),
          Container(
            width: 80,
            color: Colors.blue,
            child: const AspectRatio(aspectRatio: 1,),
          ),
          Container(
            width: 100,
            color: Colors.yellow,
            child: const AspectRatio(aspectRatio: 1,),
          ),
        ],
      ) ,
    );
  }
}

6.Stack

• 视图叠着排列，z方向
• 方向，由里到外
• 一般设置alignment来设置子部件显示的位置
• 需要设置宽高或依赖子部件宽高撑大
• Positioned，在Stack下也可以使用Positioned来设置小部件位置

class StackDemo extends StatelessWidget {

  final bool isShowPositioned;

  const StackDemo(this.isShowPositioned);

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.grey[400],
      width: MediaQuery.of(context).size.width,
      height: MediaQuery.of(context).size.height - kToolbarHeight - _statusBarHeight,
      child: Stack(
        alignment: Alignment.center,
        children: [
          Container(
            width: 200,
            height: 200,
            color: Colors.red,
          ),
          Container(
            width: 150,
            height: 150,
            color: Colors.blue,
          ),
          Container(
            width: 100,
            height: 100,
            color: Colors.yellow,
          ),
          if (isShowPositioned) Positioned(
            right: 0,
            width: 50,
            height: 150,
            top: 150,
            child: Container(
              color: Colors.purple,
            )),
        ],
      ),
    );
  }
}

stack_normal.png	stack_positioned.png

7. AspectRatio

• 设置当前部件的宽高比。注意只会影响当前部件，不会影响子部件
• 当父部件宽高都已经设置后，设置的宽高比失效

Container(
  width: 200,
  height: 150,
  color: Colors.red,
  child: const AspectRatio(aspectRatio: 1,), //失效
)

8.Expanded

• 在主轴上不会剩余间隙，将会被Expanded拉伸。设置后，主轴小部件之间间距将变为0
• flex为弹性系数，系数越大拉伸的距离占比越大。主轴方向下的所有Expanded按照其flex的比例来分割全部的空闲空间
• 这里使用Row来演示

class ExpandedDemo extends StatelessWidget {

  final bool isRow;

  const ExpandedDemo({required this.isRow});

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.grey[400],
      alignment: Alignment.center,
      child: isRow ? Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Container(
            width: 60,
            color: Colors.red,
            child: const AspectRatio(aspectRatio: 1,),
          ),
          Expanded( //蓝色在主轴上填满
            child: Container(
              color: Colors.blue,
              child: const AspectRatio(aspectRatio: 1,),
            ),),
          Container(
            width: 100,
            color: Colors.yellow,
            child: const AspectRatio(aspectRatio: 1,),
          ),
        ],
      ) :
      Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Container(
            width: 60,
            color: Colors.red,
            child: const AspectRatio(aspectRatio: 1,),
          ),
          Expanded( //蓝色在主轴上填满
            child: Container(
              width: 80,
              color: Colors.blue,
              child: const AspectRatio(aspectRatio: 1,),
            ),
          ),
          Container(
            width: 100,
            color: Colors.yellow,
            child: const AspectRatio(aspectRatio: 1,),
          ),
        ],
      ) ,
    );
  }
}

row_expanded.png	column_expanded.png

9.margin&padding

• margin，外边距。影响当前部件的内容边距
• padding，内边距。影响当前子部件的内容边距