如何解决PreferredSize颤振中的零参数构造函数错误？

Question

我正在处理一个使用自定义AppBar并因此使用PreferredSize的项目，但我得到了一个错误，说明：

The superclass 'PreferredSize' doesn't have a zero argument constructor. Try declaring a zero argument constructor in 'PreferredSize', or explicitly invoking a different constructor in 'PreferredSize'.

下面是我的部分代码：

class CustomAppBar extends PreferredSize {
  final Widget child;
  final double height;


  CustomAppBar({required this.child, required this.height}); //getting error on this line

  @override
  Size get preferredSize => Size.fromHeight(height);

  @override
  Widget build(BuildContext context) {
    return Container()
}
}

编辑:删除PreferredSize后，得到了以下错误：

The named parameter 'child' isn't defined. Try correcting the name to an existing named parameter's name, or defining a named parameter with the name 'child'.

appBar: 
PreferredSize(
preferredSize:Size.fromHeight(95),
child:
AppBar(
  
  child: Column(
    children: <Widget>[
      SizedBox(height: 40),
      Row(
        children: <Widget>[
          Builder(
            builder: (context) => FlatButton.icon(
                onPressed: () => Scaffold.of(context).openDrawer(),
                icon: Icon(Icons.menu),
                label: Text('')),
          ),
          SizedBox(width: 60),
          Text('Times ',
              style: GoogleFonts.blackHanSans(
                  textStyle:
                      TextStyle(color: Colors.black, fontSize: 20))),
          Image.asset(
            'assets/newss.png',
            height: 50,
          ),
        ],
      )

Answer 1

您甚至不必扩展PreferredSize，只需将appBar或任何其他小部件封装在PreferredSize中，只需指定其高度即可。

PreferredSize(
            preferredSize: Size.fromHeight(72),
            child: AppBar(
              title: Text(title, style: TextStyles.h1),
              centerTitle: false,
              elevation: 0,
              brightness: Brightness.light,
              backwardsCompatibility: false,
              bottom: bottomAppBarWidget,
            ))