处理手势时引发了以下断言： Scaffold.of() 使用不包含 Scaffold 的上下文调用

Question

import 'package:flutter/material.dart';

import 'dashboard.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: SafeArea(
        child: Scaffold(
          appBar: AppBar(
            leading: IconButton(
              icon: Icon(Icons.accessible),
              onPressed: () => Scaffold.of(context).openEndDrawer(),
            ),
            title: Text('Sorted.'),
            backgroundColor: Color(0xff0A3D62),
          ),
          drawer: Drawer(
            child: ListView(
              padding: EdgeInsets.zero,
              children: <Widget>[
                new UserAccountsDrawerHeader(
                  accountName: new Text('XYZ'),
                  accountEmail: new Text('XYZ@gmail.com'),
                  currentAccountPicture: new CircleAvatar(),
                )
              ],
            ),
          ),
          body: Center(child: Home()),
        ),
      ),
    );
  }
}

Error:

The following assertion was thrown while handling a gesture:
Scaffold.of() called with a context that does not contain a Scaffold.

No Scaffold ancestor could be found starting from the context that was passed to Scaffold.of(). This usually happens when the context provided is from the same StatefulWidget as that whose build function actually creates the Scaffold widget being sought.

The error fires when I try to open the drawer from the icon. Please help me resolve this. Thanks in advance!

Answer 1

@rkdupr0n is correct in saying that your context variable doesn't have a Scaffold ancestor. context is currently referring to what's being passed by the outer build function, which doesn't have Scaffold as an ancestor, it only contains it. So you need to get a BuildContext that has Scaffold the scaffold you already have in your tree as it's ancestor. To do this you can use a Builder widget to wrap the area that needs this context:

AppBar(
  leading: Builder(
    builder: (context) {//NEW CONTEXT OBTAINED HERE
      return IconButton(
        icon: Icon(Icons.accessible),
        onPressed: () => Scaffold.of(context).openEndDrawer(),
      );
    }
  ),
  ...
),