FLUTTER：-我需要从Navigator.push（）方法之后的方法返回小部件

Question

我已经使用Flutter和BLOC架构制作了一个登录应用程序。如果登录成功，则需要将小部件返回到支架，还想使用Navigator.push（）导航到下一个屏幕。

我尝试了以下方法：-

方法1：-

Navigator.push(context,MaterialPageRoute(builder: (context) => DashboardPage()));
return ButtonWidget();

但是这会导致您转移到下一屏幕时无法设置小部件的错误。

方法2：-

Future.delayed(
        Duration(days: 1200),
        () => 
              Navigator.push(context,
                  MaterialPageRoute(builder: (context) => DashboardPage())),
            ));
return ButtonWidget();

但是它会使将来的代码每1.2秒运行一次。

3。方法3：-

var cancellableCompleter = CancelableCompleter(onCancel:()print("onCancel"););
    cancellableCompleter.complete(
      //Future.value("future result"));
      Future.delayed(
        Duration(days: 1200),
        () => 
              print("i am here"),
              Navigator.push(context,
                  MaterialPageRoute(builder: (context) => DashboardPage())),
            ));
    cancellableCompleter.operation.value.then((value)=>print(value));
    cancellableCompleter.operation.value.whenComplete(()=>print("Completed"));
    return ButtonWidget();

但是它不会实例化Navigator.push（）方法。即使“我在这里”也不会打印。

我也尝试过CancelableOperation，但它给出了与方法2相同的错误。

完整代码

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:fluttertoast/fluttertoast.dart';
import 'package:sales_app/bloc/bloc.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:async/async.dart';

import 'dashboard_page.dart';

class LoginPage extends StatefulWidget 
  @override
  State<StatefulWidget> createState() 
    return _LoginPageState();
  


class _LoginPageState extends State<LoginPage> 
  String _email;
  String _password;
  LoginBloc bloc = LoginBloc();
  final blue_color = Color(0xff4490E8);
  final formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) 
    return Scaffold(
      body: BlocProvider(
        builder: (context) => bloc,
        child: Container(
          decoration: BoxDecoration(color: blue_color),
          child: Padding(
            padding: const EdgeInsets.all(20.0),
            child: Form(
              key: formKey,
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                crossAxisAlignment: CrossAxisAlignment.center,
                children: <Widget>[
                  Text(
                    "Log In",
                    style: TextStyle(color: Colors.white, fontSize: 30),
                  ),
                  SizedBox(
                    height: 50,
                  ),
                  TextFormField(
                      autovalidate: true,
                      style: TextStyle(color: blue_color),
                      onSaved: (email) => this._email = email,
                      keyboardType: TextInputType.emailAddress,
                      initialValue: "saurav.vidyarthi@connexrm.com",
                      validator: (val) =>
                          RegExp(r"^[a-zA-Z0-9.]+@[a-zA-Z0-9]+\.[a-zA-Z]+")
                                  .hasMatch(val)
                              ? null
                              : "Invalid Email",
                      decoration: InputDecoration(
                        filled: true,
                        helperStyle: TextStyle(color: blue_color),
                        labelStyle: TextStyle(color: blue_color),
                        labelText: "Email Id",
                        hintText: "e.g. joe@gmail.com",
                        hintStyle: TextStyle(color: blue_color),
                        prefixIcon: Icon(Icons.email, color: blue_color),
                        fillColor: Colors.white,
                        /*border: OutlineInputBorder(
                            borderSide:
                            BorderSide(color: const Color(0xffffffff)))),*/
                      )),
                  SizedBox(height: 15.0),
                  TextFormField(
                      style: TextStyle(color: blue_color),
                      obscureText: true,
                      autovalidate: true,
                      initialValue: "Saurav@1",
                      onSaved: (password) => _password = password,
                      validator: (val) => val.length < 6
                          ? "Password must be of at least 6 char."
                          : null,
                      decoration: InputDecoration(
                          filled: true,
                          labelStyle: TextStyle(color: blue_color),
                          hintStyle: TextStyle(color: blue_color),
                          prefixIcon: Icon(Icons.lock, color: blue_color),
                          fillColor: Colors.white,
                          /* border: OutlineInputBorder(
                              borderSide:
                              BorderSide(color: const Color(0xffffffff))),*/
                          labelText: "Password",
                          hintText: "*******")),
                  SizedBox(height: 25.0),
                  BlocBuilder(
                    bloc: bloc,
                    builder:
                        (BuildContext buildContext, LoginState loginState) 
                      print(loginState.toString());
                      if (loginState is InitialLoginState)
                        return _buildInitialState();
                      else if (loginState is LoggingInState)
                        return _buildLoadingState();
                      else if (loginState is LoginSuccessState) 
                        LoginSuccessState state = loginState;
                        return _buildSuccessState(state.user.StatusText);
                       else 
                        LoginFailedState state = loginState;
                        return _buildFailureState(state.user.StatusText);
                      
                    ,
                  )
                ],
              ),
            ),
          ),
        ),
      ),
    );
  

  void _onButtonPressed() 
    if (formKey.currentState.validate()) 
      formKey.currentState.save();
      bloc.dispatch(GetUser(_email, _password));
     else 
      Fluttertoast.showToast(msg: "Please enter a valid email and password");
    
  

  Widget _buildInitialState() 
    return RaisedButton(
        onPressed: _onButtonPressed,
        color: Colors.white,
        child: Text(
          "Log In",
          style: TextStyle(color: blue_color),
        ));
  

  Widget _buildLoadingState() 
    return CircularProgressIndicator(backgroundColor: Colors.white);
  

  Widget _buildFailureState(message) 
    Fluttertoast.showToast(msg: message);
    return RaisedButton(
        onPressed: _onButtonPressed,
        color: Colors.white,
        child: Text(
          "Log In",
          style: TextStyle(color: blue_color),
        ));
  

  Widget _buildSuccessState(message) 
    Fluttertoast.showToast(msg: message);
    _setAuthState();
    var cancellableCompleter = CancelableCompleter(onCancel:()print("onCancel"););
    cancellableCompleter.complete(
      //Future.value("future result"));
      Future.delayed(
        Duration(days: 1200),
        () => 
              print("i am here"),
              Navigator.push(context,
                  MaterialPageRoute(builder: (context) => DashboardPage())),
            ));
    cancellableCompleter.operation.value.then((value)=>print(value));
    cancellableCompleter.operation.value.whenComplete(()=>print("Completed"));
    return RaisedButton(
      onPressed: _onButtonPressed,
      color: Colors.white,
      child: Text(
        "Log In",
        style: TextStyle(color: blue_color),
      ),
    );
  

  _setAuthState() async 
    SharedPreferences sharedPreferences = await SharedPreferences.getInstance();
    await sharedPreferences.setBool("isLoggedIn", true);
  

  @override
  void dispose() 
    super.dispose();
    bloc.dispose();