如何转换Widget？到Widget

Question

• 下面的代码会出错，返回值是Widget吗？而不是Widget。我想要能强迫Widget？但怎么做呢？

/// Get the parent widget in the subtree
class ContextRoute extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text("Context test"),
      ),
      body: Container(
        child: Builder(builder: (context) {
          // Find the nearest parent up in the Widget tree `Scaffold` widget
          Scaffold? scaffold = context.findAncestorWidgetOfExactType<Scaffold>();
          // Return the title of AppBar directly, here is actually Text ("Context test")
          Widget? widget1 = (scaffold!.appBar as AppBar).title;
          return widget1;
        }),
      ),
    );
  }
}

Answer 1

虽然最短的方法是使用Bang !运算符

Widget widget = nullableWidget!;

但我建议你用?.来预防这一错误

Widget widget = nullableWidget ?? Container(); // Or some other widget. 

回答你的问题：

return widget ?? Container(); // Safe
return widget!; // Could cause runtime error.

Answer 2

使用空断言运算符/邦运算符( ! )

return widget1!;