前言

目前Flutter常见的布局方式主要有4种：1、线性布局 2、流式布局 3、弹性布局 4、层叠布局

今天我们主要介绍流式布局

线性布局

弹性布局

层叠布局

流式布局

我们把超出屏幕显示范围会自动换行的布局称为流式布局
关键字Wrap、Flow

流式布局Wrap关键字

 body: Wrap(
          direction: Axis.horizontal,
          children: [
            Container(
              margin: EdgeInsets.only(left: 30,top: 30),
              width: 100,
              height: 100,
              color: Colors.red,
              child: Text("1",style:TextStyle(
                color: Colors.white,
                fontSize: 60,
              )),
            ),
            Container(
              margin: EdgeInsets.only(left: 30,top: 30),
              width: 100,
              height: 100,
              color: Colors.yellow,
              child: Text("3",style:TextStyle(
                color: Colors.white,
                fontSize: 60,
              )),
            ),
            Container(
              margin: EdgeInsets.only(left: 30,top: 30),
              width: 100,
              height: 100,
              color: Colors.blue,
              child: Text("3",style:TextStyle(
                color: Colors.white,
                fontSize: 60,
              )),
            ),
            Container(
              margin: EdgeInsets.only(left: 30,top: 30),
              width: 100,
              height: 100,
              color: Colors.blue,
              child: Text("4",style:TextStyle(
                color: Colors.white,
                fontSize: 60,
              )),
            ),
          ],
        )

流式布局自动换行

流式布局Flow关键字

return Scaffold(
        appBar: AppBaseBar("流式布局"),
        body: Flow(
            delegate: MyFlowDelegate(boxSize: 80),
            children: List.generate(15, (index){
            return Box(index, 80);
          })
        )
    );

创建Box 代码

  /*一个正方形*/
  Widget Box(index,double boxSize) => Container(
    width: boxSize,
    height: boxSize,
    alignment: Alignment.center,
    color: Colors.red,
    child: Text(
      index.toString(),
      style: TextStyle(
        color: Colors.white,
        fontSize: 50,
        fontWeight: FontWeight.bold,
      ),
    ),
  );

delegate 实现

class MyFlowDelegate extends FlowDelegate {
  MyFlowDelegate({this.boxSize});
  final boxSize;
  @override
  void paintChildren(FlowPaintingContext context) {
    /*屏幕宽度*/
    var screenW = context.size.width;
    double padding = 5; //间距
    double offsetX = padding; //x坐标
    double offsetY = padding; //y坐标
    for (int i = 0; i < context.childCount; i++) {
      /*如果当前x左边加上子控件宽度小于屏幕宽度  则继续绘制  否则换行*/
      if (offsetX + boxSize < screenW) {
        /*绘制子控件*/
        context.paintChild(I,
            transform: Matrix4.translationValues(offsetX, offsetY, 0));
        /*更改x坐标*/
        offsetX = offsetX + boxSize + padding;
      } else {
        /*将x坐标重置为margin*/
        offsetX = padding;
        /*计算y坐标的值*/
        offsetY = offsetY + boxSize + padding;
        /*绘制子控件*/
        context.paintChild(I,
            transform: Matrix4.translationValues(offsetX, offsetY, 0));
      }
    }
  }
  @override
  bool shouldRepaint(FlowDelegate oldDelegate) {
    return true;
  }
}

UI效果显示