flutter - 将2个变量从2个差异屏幕传递到1个屏幕

Question

我有Home()，Category()，Region()类

要添加类别，请导航至Category()并添加区域，请导航至Region()

我想将类别内的cat值和区域内的城市值传递到主屏幕，但是我收到此错误:

Compiler message:
lib/Screens/regions.dart:32:95: Error: Too few positional arguments: 2 required, 1 given.
                Navigator.pushReplacement(context, MaterialPageRoute(builder: (context)=>Home(city)));

这是主屏幕:

 class Home extends StatefulWidget {

  final String sRegion;
  final String sCategory;

  Home(this.sRegion,this.sCategory, {Key key}):super(key: key);
  @override
  _HomeState createState() => _HomeState();
}

class _HomeState extends State<Home> {
 @override
  Widget build(BuildContext context) {
return Directionality(
  textDirection: TextDirection.rtl,
  child: Scaffold(
    body: Center(
      child: Text(cat + city),
    ),
  ),
);
  }
}

类别屏幕:

 class Category extends StatefulWidget {

  @override
  _CategoryState createState() => _CategoryState();
}

class _CategoryState extends State<Category> {
 @override
  Widget build(BuildContext context) {
 String cat = 'General';
return Directionality(
  textDirection: TextDirection.rtl,
  child: Scaffold(
    body: Center(
      child: FlatButton( onPressed: (){
            Navigator.pushReplacement(context, MaterialPageRoute(builder: (context)=>Home(cat)));
          },),
    ),
  ),
);
  }
}

区域屏幕:

     class Region extends StatefulWidget {

  @override
  _RegionState createState() => _RegionState();
}

class _RegionState extends State<Region> {
 @override
  Widget build(BuildContext context) {
 String city = 'London';
return Directionality(
  textDirection: TextDirection.rtl,
  child: Scaffold(
    body: Center(
      child: FlatButton( onPressed: (){
            Navigator.pushReplacement(context, MaterialPageRoute(builder: (context)=>Home(city)));
          },),
    ),
  ),
);
  }
}

Answer 1

Home具有两个必须的位置参数(sRegion和sCategory)。这些不是可选的，您必须提供它们。

Navigator.pushReplacement(context, 
     MaterialPageRoute(builder: (context)=>Home(city, cat)));

请注意，我在 cat构造函数中添加了 Home。如果这些参数中的任何一个是可选的，则需要重写构造函数签名。

如果要使这些参数中的任何一个为可选，请将其转换为命名参数

Home({this.sRegion,this.sCategory, Key key}):super(key: key);