Question

我是新手，我希望整理我的文件夹以编写简洁的代码。我试图将页面分为三个部分：

login_view.dart （此视图将显示为登录视图，并将调用在login_builder.dart中定义的函数以构建其每个小部件）
login_builder.dart （包含由login_view.dart调用以创建小部件的函数定义）
login_state.dart （用于状态管理）

但是，当我在login_builder.dart（在login_view.dart小部件树之外）定义的函数中调用 Provider.of（context）时，它总是抛出 ProviderNotFoundException >

// login_view.dart

import 'package:discover/ui/views/login/login_builder.dart';
import 'package:discover/ui/views/login/login_state.dart';
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';

class Login extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider<LoginState>(
      create: (context) => LoginState(),
      child: buildLoginForm(context), 
    );
  }
}

// login_builder.dart

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:discover/ui/views/login/login_state.dart';

Widget buildLoginForm(BuildContext context) {
  var loginState = Provider.of<LoginState>(context);
  return Form(
    child: Column(
      children: <Widget>[
        TextFormField(
          onChanged: (value) => loginState.userName = value,
        )
      ],
    ),
  );
}

// login_state.dart

import 'package:flutter/material.dart';

class LoginState extends ChangeNotifier {
  String _userName = "";

  String get userName => _userName;

  set userName(String userName) {
    _userName = userName;
  }
}

//调试控制台

════════ Exception caught by widgets library ═══════════════════════════════════
The following ProviderNotFoundException was thrown building Login(dirty):
Error: Could not find the correct Provider<LoginState> above this Login Widget

To fix, please:

  * Ensure the Provider<LoginState> is an ancestor to this Login Widget
  * Provide types to Provider<LoginState>
  * Provide types to Consumer<LoginState>
  * Provide types to Provider.of<LoginState>()
  * Ensure the correct `context` is being used.

If none of these solutions work, please file a bug at:
https://github.com/rrousselGit/provider/issues

The relevant error-causing widget was
    Login
When the exception was thrown, this was the stack
Provider.of
buildLoginForm
Login.build
StatelessElement.build
ComponentElement.performRebuild

Answer 1

您传递给login_builder的context与传递给login_view的上下文相同，因此它位于小部件树的上方，在其中插入了ChangeNotifierProvider，这就是为什么您不能用Provider.of找到它。为了使它按您希望的方式工作，您需要利用Builder小部件来获取提供者下方存在的新BuildContext：

class Login extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ChangeNotifierProvider<LoginState>(
      create: (context) => LoginState(),
      child: Builder(builder: buildLoginForm), 
    );
  }
}

现在，传递给buildLoginForm的上下文将是Builder（位于提供者下方）的上下文，而不是Login小部件（位于提供者上方的上下文）。 / p>

Flutter：无法从定义到另一个文件的函数调用Provider <T> .of（context）。 ProviderNotFoundException

1 个答案: