Question

我收到此异常

发生异常。 NoSuchMethodError（NoSuchMethodError：方法'ancestorStateOfType'在null上调用。接收者：null 尝试调用：ancestorStateOfType（'TypeMatcher'的实例））

使用针对RaisedButton的onPressed函数传递的自定义方法（navigateToLogin），但是，当我直接在onPressed =（）{... Navigation code ..}上编写相同的导航时，它可以正常工作。是因为没有获取上下文吗？

import 'package:credit/src/pages/credit/home.dart';
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:flutter/gestures.dart';
import 'dart:convert';

class LandingPage extends StatelessWidget {
  BuildContext context;

  @override
  Widget build(BuildContext context) {
    //return HomePage();  // Un coment this method for Homepage
    String loginTxt = "Login";

    // Set login value on click of Login button
    setLoginValue() async {
      SharedPreferences loginCheck = await SharedPreferences.getInstance();
      await loginCheck.setString("userstatus", "loggedin");
      print("Set login value");
      print(loginCheck.getString("userstatus"));
    }

    return WillPopScope(
        onWillPop: () {
          SystemNavigator.pop();
          return Future.value(false);
        },
        child: SafeArea(
            child: MaterialApp(
                debugShowCheckedModeBanner: false,
                home: Scaffold(
                    appBar: PreferredSize(
                      preferredSize: Size.fromHeight(35),
                      child: AppBar(
                        backgroundColor: Colors.lightBlueAccent,
                        title: Text("Select Language"),
                        automaticallyImplyLeading: false,
                        primary: false,
                      ),
                    ),
                    bottomNavigationBar: BottomAppBar(
                      child: RaisedButton(
                        onPressed: navigateToLogin(),
                        child: Row(
                          mainAxisAlignment: MainAxisAlignment.center,
                          children: <Widget>[
                            Container(
                              child: new Text("Continue",
                                  style: TextStyle(fontSize: 20)),
                            ),
                            Container(
                              child: new Icon(Icons.navigate_next),
                            )
                          ],
                        ),
                        padding: EdgeInsets.fromLTRB(0, 20, 0, 20),
                        color: Colors.lightBlueAccent,
                        splashColor: Colors.orangeAccent,
                      ),
                    ),
                    body: Column(
                      children: <Widget>[],
                    )))));
  }

  navigateToLogin() {
    Navigator.of(context)
        .push(MaterialPageRoute<Null>(builder: (BuildContext context) {
      return HomePage();
    }));
  }
}

Answer 1

是的，如果您希望它能正常工作，则必须传递context作为参数：

navigateToLogin(BuildContext context) {
    Navigator.of(context)
        .push(MaterialPageRoute<Null>(builder: (BuildContext context) {
      return HomePage();
    }));
  }

当您调用它时：

onPressed: () => navigateToLogin(context);

Flutter：将Navigator.of（context）用于RaisedButton的onPressed事件时发生异常

1 个答案: