Flutter Positioned widget 导致错误 : Incorrect use of ParentDataWidget

Question

以下代码导致错误:ParentDataWidget 的使用不正确。此错误的原因是 Positioned 小部件，但我不确定为什么...

return Scaffold(
      body: Container(
        color: Colors.red,
        child: Positioned(
          left: 32.0,
          child: Container(
            width: 128.0,
            height: 128.0,
            color: Colors.yellow,
          ),
        ),
      ),
    );

Answer 1

Positioned 必须根据 documentation 在 Stack 中就是说

A widget that controls where a child of a Stack is positioned.

A Positioned widget must be a descendant of a Stack, and the path from the Positioned widget to its enclosing Stack must contain only StatelessWidgets or StatefulWidgets (not other kinds of widgets, like RenderObjectWidgets).

return Scaffold(
      body: Container(
        color: Colors.red,
        child: Stack(
          children: <Widget>[
            Positioned(
              left: 32.0,
              child: Container(
                width: 128.0,
                height: 128.0,
                color: Colors.yellow,
              ),
            ),
          ],
        ),
      ),
    );