如何在Blazor Server的后端中正确使用依赖注入? [英] How to properly use Dependency Injection in Backend in Blazor Server?

问题描述

我有一个Blazor服务，需要注入特定的"LocalStorage"服务.这样做是这样的:

I have a Blazor-service that needs a specific "LocalStorage"-service injected. It is done this way:

 public class UserApi : IUserApi
    {
        private readonly LocalStorage _localStorage;

        public UserApi(LocalStorage localStorage)
        {
            _localStorage = localStorage;
        }
...
}

将"LocalStorage"注入到Startup.cs( ConfigureServices )中:

"LocalStorage" is injected within the Startup.cs (ConfigureServices):

services.AddStorage();

(我认为可以安全地假设它可以正常工作)

(I think it is safe to assume that this works as it should)

我还在以下行中添加了自己的服务:

I also added my own service with the following line:

services.AddSingleton<IUserApi, UserApi>();

在剃须刀页面上，我注入了服务:

On the razor-page I inject my Service:

@inject IUserApi UserApi

并在那里访问功能

  private void HandleValidSubmit()
    {
        if (UserApi.Login( _loginUser.Mail, _loginUser.Password, out string error, out Guid? guid))
        {
            // DoMagic
        }
    }

当我尝试启动我的应用程序时，出现以下错误:

When I try to start my application I receive the following error:

System.AggregateException

System.AggregateException

内部异常1:

InvalidOperationException:验证服务时出错描述符'ServiceType:BlazorFood.IUserApi生存期:单例ImplementationType:BlazorFood.UserApi':无法使用作用域服务来自的"Cloudcrate.AspNetCore.Blazor.Browser.Storage.LocalStorage"单例"BlazorFood.IUserApi".

InvalidOperationException: Error while validating the service descriptor 'ServiceType: BlazorFood.IUserApi Lifetime: Singleton ImplementationType: BlazorFood.UserApi': Cannot consume scoped service 'Cloudcrate.AspNetCore.Blazor.Browser.Storage.LocalStorage' from singleton 'BlazorFood.IUserApi'.

内部异常2:InvalidOperationException:无法使用作用域服务'Cloudcrate.AspNetCore.Blazor.Browser.Storage.LocalStorage'来自单例"BlazorFood.IUserApi"

Inner Exception 2: InvalidOperationException: Cannot consume scoped service 'Cloudcrate.AspNetCore.Blazor.Browser.Storage.LocalStorage' from singleton 'BlazorFood.IUserApi'

当我从 ConfigureServices 删除AddSingleton-line时，我可以启动我的应用程序，但尝试访问包含IUserApi-Injection的剃刀页面时检索到错误:

When I remove the AddSingleton-line from ConfigureServices I can start my application but retrieve an error when trying to access the razor-page containing the IUserApi-Injection:

InvalidOperationException:无法提供属性值类型为"BlazorFood.Pages.admin.Login"的"UserApi".没有类型为"BlazorFood.IUserApi"的注册服务

InvalidOperationException: Cannot provide a value for property 'UserApi' on type 'BlazorFood.Pages.admin.Login'. There is no registered service of type 'BlazorFood.IUserApi'

要正确注入我的服务需要做什么?

What has to be done to inject my services properly?

推荐答案

这部分错误消息

无法使用单例"BlazorFood.IUserApi"中的作用域服务"Cloudcrate.AspNetCore.Blazor.Browser.Storage.LocalStorage"

Cannot consume scoped service 'Cloudcrate.AspNetCore.Blazor.Browser.Storage.LocalStorage' from singleton 'BlazorFood.IUserApi'

从文档中也可以看到

从单例中解析作用域服务很危险.处理后续请求时，可能会导致服务的状态不正确.

It's dangerous to resolve a scoped service from a singleton. It may cause the service to have incorrect state when processing subsequent requests.

参考 ASP.NET Core中的依赖项注入

注册时不要让您的服务单身，这应该可以解决问题

Don't make your service singleton when registering it and that should fix the issue

services.AddScoped<IUserApi, UserApi>();

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