在初始化程序中只能访问静态成员

Question

我不能在Scaffold 中使用GlobalKey。错误是

在初始化器中只能访问静态成员

//Global key
  final GlobalKey<ScaffoldState> _mainKey= GlobalKey<ScaffoldState>();
// List of TabBar
final List<Widget> tabBar = <Widget>[
    Column(
      children: <Widget>[
        Icon(Icons.account_balance_wallet),
        Text('flutter'),
        Text('dart')
      ],
    ),
    FlatButton(
      child: Text('Open Drawer'),
      onPressed: (){
         //( _mainKey) has a red underLine color
        _mainKey.currentState.openDrawer();
      },
    )
  ];
/*
Compiler message:
lib/Trial.dart:32:9: Error: Can't access 'this' in a field initializer to read '_mainKey'.
        _mainKey.currentState.openDrawer();*/

Answer 1

简答

替换

final _mainKey = ...; 

与

static _mainKey = ...;

---

长答案：

我建议您将 tabBar 从变量更改为方法，这样您就不需要创建变量 static。喜欢：

List<Widget> getTabBar() {
  return [
    Column(
      children: <Widget>[Icon(Icons.account_balance_wallet), Text('flutter'), Text('dart')],
    ),
    FlatButton(
      child: Text('Open Drawer'),
      onPressed: () {
        _mainKey.currentState.openDrawer();
      },
    )
  ];
}