问题描述
我想创建一个具有 authentication service
的应用程序,该应用程序具有不同的权限和功能(例如消息),具体取决于用户角色.
I want to create an app that has an authentication service
with different permissions and functions (e.g. messages) depending on the user role.
所以我为用户和登录管理创建了一个 Provider
并为用户可以看到的消息创建了另一个.
So I created one Provider
for the user and login management and another one for the messages the user can see.
现在,我想在用户登录时(一次)获取消息.在 Widgets
中,我可以通过 Provider.of<T>(context)
,我猜这是一种 Singleton
.但是我怎样才能从另一个类(在这种情况下是另一个提供者)访问它?
Now, I want to fetch the messages (once) when the user logs in. In Widgets
, I can access the Provider via Provider.of<T>(context)
and I guess that's a kind of Singleton
. But how can I access it from another class (in this case another Provider)?
推荐答案
感谢您的回答.同时,我用另一种解决方案解决了它:
Thanks for your answer. In the meanwhile, I solved it with another solution:
在 main.dart
文件中,我现在使用 ChangeNotifierProxyProvider
而不是 ChangeNotifierProvider
作为依赖提供者:
In the main.dart
file I now use ChangeNotifierProxyProvider
instead of ChangeNotifierProvider
for the depending provider:
// main.dart
return MultiProvider(
providers: [
ChangeNotifierProvider(builder: (_) => Auth()),
ChangeNotifierProxyProvider<Auth, Messages>(
builder: (context, auth, previousMessages) => Messages(auth),
initialBuilder: (BuildContext context) => Messages(null),
),
],
child: MaterialApp(
...
),
);
现在,当登录状态更改并通过身份验证提供程序时,消息提供程序将被重建:
Now the Messages provider will be rebuilt when the login state changes and gets passed the Auth Provider:
class Messages extends ChangeNotifier {
final Auth _authProvider;
List<Message> _messages = [];
List<Message> get messages => _messages;
Messages(this._authProvider) {
if (this._authProvider != null) {
if (_authProvider.loggedIn) fetchMessages();
}
}
...
}
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