Flutter Failed assertion: line 1

报错 ：Failed assertion: line 1785 pos 12: 'hasSize'

原因：1. SingleChildScrollView 嵌套 ListView、GridView报错 ，SingleChildScrollView 和 ListView 都有滚动
属性physics 他们默认是都是可以滚动的
2. SingleChildScrollView 添加了Expanded或者Flexible

解决方法: 1. 增加shrinkWrap: true 和 physics: NeverScrollableScrollPhysics()即可。

SingleChildScrollView(
  child: Column(
    children: <Widget>[
      GridView.count(
        crossAxisCount: 2,
        children: <Widget>[],
        physics: NeverScrollableScrollPhysics(),
        shrinkWrap: true,
      ),
      ListView.builder(
        itemCount: 10,
        itemBuilder: (context, index) {
          return Text("test");
        },
        physics: NeverScrollableScrollPhysics(),
        shrinkWrap: true,
      )
    ],
  ),
)

2.固定父级组件的高度

SingleChildScrollView(
    child: ConstrainedBox(
        constraints: BoxConstraints(maxHeight: MediaQuery.of(context).size.height),
        child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            crossAxisAlignment: CrossAxisAlignment.stretch,
            children: <Widget>[
                Expanded(
                    child: Text('Hello World!'),
                ),
            ],
        ),
    )
)