未在构建时启动ChangeNotifierProxyProvider

问题描述

我试图了解Flutter中的多提供商.在我的应用中，一个提供商需要根据另一提供商的值进行更改.

I'm trying to understand multiproviders in Flutter. In my App, one Provider need to change based on a value from an other Provider.

AuthProvider在构建时在小部件树中更高一级启动.如果可能的话，可以自动登录，就像超级按钮一样.

AuthProvider gets initiated higher up in the widget tree on build. Works like a charm with automatic sign in if possible...

在较低位置的小部件中，我尝试启动其他两个提供程序.其中之一，WhatEver，不依赖于其他数据，而是像应该使用ChangeNotifierProvider一样在构建时启动.

In a lower placed widget, I try to initiate two other Providers. One, WhatEver, is not depended on other data and gets initiated on build like it is supposed to using ChangeNotifierProvider.

ProductList但是取决于AuthProvider.如果登录状态更改，则ProducList应该相应地更新.

ProductList however is depended on AuthProvider. If log in status is changed, the ProducList should update accordingly.

在我的尝试中，我发现，即在SO上发现，ChangeNotifierProxyProvider是正确的方法.但是，当我运行该应用程序时，似乎在构建小部件时未启动ChangeNotifierProxyProvider的创建"部分.似乎在读取或写入ProductList提供程序之前，不会启动它.

In my attempts, I've found out, ie found on SO, that ChangeNotifierProxyProvider is the right way to go. But when I run the App, it seems like the 'create'-part of ChangeNotifierProxyProvider is not initiated when the widget gets build. It seems like the ProductList provider is not initiated until it's read or written to.

我使用MultiProviders和ChangeNotifierProxyProvider误解了什么?

What have I misunderstood using MultiProviders and ChangeNotifierProxyProvider?

return MultiProvider(
        providers: [
          ChangeNotifierProvider<WhatEver>(create: (context) => WhatEver()),
          ChangeNotifierProxyProvider<AuthProvider, ProductList>(
            create: (_) => ProductList(Provider.of<AuthProvider>(context, listen: false)),
            update: (_, auth, productList) => productList..reloadList(auth)
          ),
        ],

ProductList看起来像这样:

The ProductList looks like this:

final AuthProvider _authProvider;

static const String _TAG = "Shop - product_list.dart : ";

ProductList(this._authProvider) {
    print(_TAG + "ProductList Provider initiated");
    reloadList(this._authProvider);
}

void reloadList(AuthProvider authProvider) {
    print(_TAG + "ProductList reload started");
    if (authProvider.user==null) {
        print(_TAG + "ProductList: _authProvider == null");
        _loadBuiltInList();
    } else {
        print(_TAG + "ProductList: user = " + authProvider.user.displayName);
        _loadFirestoreList();
    }
}

推荐答案

我有执行此操作的代码:

I have code that does this:

ChangeNotifierProxyProvider<AuthService, ProfileService>(
  create: (ctx) => ProfileService(),
  update: (ctx, authService, profileService) =>
      profileService..updateAuth(authService),
),

我的ProfileService()在构造AuthService时并不依赖于它.该代码可以正常工作:)

My ProfileService() does not rely on AuthService being available when it is constructed. The code works fine :)

ChangeNotifierProxyProvider文档明确描述了这种方法:

The ChangeNotifierProxyProvider documentation explicitly describes this approach:

这篇关于未在构建时启动ChangeNotifierProxyProvider的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！