依赖注入问题 - 初始化远程服务连接

Question

在我的 .Net Core 3.0 应用程序中，我想使用 Microsoft Graph Nuget 库。我创建了一个连接类，它使用[MSAL][1] 对我的应用程序进行身份验证，然后创建连接并返回它。我的想法是使用Dependency Injection 在构造函数中注入这个连接对象。但是，由于创建连接的方法是异步的，我似乎有一个问题，如何在构造函数中使用它。

我的连接类

 public class AuthorizeGraphApi: IAuthorizeGraphApi
    {
        private readonly IConfiguration _config;

        public AuthorizeGraphApi(IConfiguration config)
        {
            _config = config;
        }

        public async Task<GraphServiceClient> ConnectToAAD()
        {
            string accessToken = await GetAccessTokenFromAuthorityAsync();
            var graphServiceClient = new GraphServiceClient(new DelegateAuthenticationProvider((requestMessage) => {
                requestMessage
                    .Headers
                    .Authorization = new AuthenticationHeaderValue("Bearer", accessToken);

                return Task.FromResult(0);
            }));
            return graphServiceClient;
        }

        private async Task<string> GetAccessTokenFromAuthorityAsync()
        {
            // clientid, authUri, etc removed for this example.
            IConfidentialClientApplication _conn;
            _conn = ConfidentialClientApplicationBuilder.Create(clientId)
                .WithClientSecret(clientSecret)
                .WithAuthority(new Uri(authUri))
                .Build();
           string[] scopes = new string[] { $"api://{clientId}/.default" };

           AuthenticationResult result = null;
           // AcquireTokenForClient only has async method.
           result = await _conn.AcquireTokenForClient(scopes)
              .ExecuteAsync();

           return result.AccessToken;
        }
    }

我的图表服务发送请求

public class AzureIntuneService
{
    private readonly IAuthorizeGraphApi _graphClient;
    public AzureIntuneService(IAuthorizeGraphApi client)
    {
        //Gives: cannot implicitely convert to Threading.Tasks.Task.... error
        _graphClient = client.ConnectToAAD();
    }

    public async Task<IList<string>> GetAADInformationAsync()
    {
        // then here, use the graphClient object for the request...
        var payload = await _graphClient.Groups.Request().GetAsync();
        return payload
    }
}

我在我的启动中注册了上述类如下：

services.AddScoped<IAuthorizeGraphApi, AuthorizeGraphApi>();

我的想法是这样，我不需要在每个方法中调用 _graphClient。如何以正确的方式注入连接对象？或者关于这个（注入连接对象）的最佳实践是什么？

Answer 1

一种方法是存储对Task 的引用，并确保使用该连接的任何公共方法都是async：

public class AzureIntuneService
{
    private readonly Task<GraphServiceClient> _graphClientTask;
    public AzureIntuneService(IAuthorizeGraphApi client)
    {
        _graphClientTask = client.ConnectToAAD();
    }

    public async Task<IList<string>> GetAADInformationAsync()
    {
        var client = await _graphClientTask; // Get the client when connected
        var payload = await client.Groups.Request().GetAsync();
        return payload;
    }
}

Answer 2

构造函数不是async，并且永远不应该用于初始化任何async。解决此问题的唯一方法是通过执行.Result 进行异步同步，这总是一个问题。

在您的情况下，接受DelegateAuthenticationProvider 的GraphServiceClient 接受AuthenticateRequestAsyncDelegate。这允许您有一个async 委托来构造客户端。

所以现在你可以做

new DelegateAuthenticationProvider(async requestMessage =>  
    {
        string accessToken = await GetAccessTokenFromAuthorityAsync(); 
        //rest of code here
    } 
)

这允许您将ConnectToAAD 签名更改为只返回GraphServiceClient 而不是Task<GraphServiceClient>。

Answer 3

当您需要异步数据时，您必须远离常规构造函数并创建工厂方法（私有静态函数）。如下所示：

public sealed class MyClass
{
  private MyData asyncData;
  private MyClass() { ... }

  private async Task<MyClass> InitializeAsync()
  {
    asyncData = await GetDataAsync();
    return this;
  }

  public static Task<MyClass> CreateAsync()
  {
    var ret = new MyClass();
    return ret.InitializeAsync();
  }
}

public static async Task UseMyClassAsync()
{
  MyClass instance = await MyClass.CreateAsync();
  ...
}

更多：https://blog.stephencleary.com/2013/01/async-oop-2-constructors.html