Question

运行.Net Core 2.0 API端点低于错误时。

找不到适合类型'RestDataService'的构造函数。确保类型是具体的，并为公共构造函数的所有参数注册服务。

 public partial class RestDataService : IRestDataService
    {
        private static HttpClient _client;
        private static AppConfiguration _configuration;
        private const short MaxRetryAttempts = 3;
        private const short TimeSpanToWait = 2;

        public RestDataService(AppConfiguration configuration)
        {
            _client = configuration.HttpClient;
            _configuration = configuration;
        }
........

我的启动类是这样的：

  // This method gets called by the runtime. Use this method to add services to the container.
        public void ConfigureServices(IServiceCollection services)
        {

            var config = new AppConfiguration
            {
                Environment = Configuration["environment"],
            };

            services.AddMvc().AddJsonOptions(o => o.SerializerSettings.NullValueHandling = NullValueHandling.Include);
            services.AddMemoryCache();
            services.AddCors();
            services.AddAutoMapper(AppDomain.CurrentDomain.GetAssemblies());
                services.AddSingleton(Configuration);
                services.AddSingleton(config);
            services.AddLogging();
            services.AddTransient<IRestDataService, RestDataService>();

services.AddHttpClient<IRestDataService, RestDataService>()
                .AddPolicyHandler(request => request.Method == HttpMethod.Get ? retryPolicy : noOp);

有什么建议要摆脱这个？构造函数已经公开，并且所有参数都已在启动文件中注册

Answer 1

我收到错误“找不到适合类型 '' 的构造函数。” 在意外生成 protected 构造函数而不是 public 之后 构造函数。将其标记回 public 修复了它。

Answer 2

您必须定义要用于IRestDataService的接口的具体类。所以，这样定义。

services.AddTransient<IRestDataService, RestDataService>();

在AppConfiguration之前删除静态关键字。

private readonly AppConfiguration _configuration;

Answer 3

对于AddHttpClient，您需要为HttpClient提供RestDataService参数。并且，您需要注册AppConfiguration。

RestDataService

public class RestDataService: IRestDataService
{
    private static HttpClient _client;
    private static AppConfiguration _configuration;
    private const short MaxRetryAttempts = 3;
    private const short TimeSpanToWait = 2;

    public RestDataService(AppConfiguration configuration
        , HttpClient client)
    {
        _client = configuration.HttpClient;
        _configuration = configuration;
    }
}

Startup.cs

var config = new AppConfiguration
{
    Environment = Configuration["environment"],
};

services.AddSingleton(typeof(AppConfiguration), config);
services.AddHttpClient<IRestDataService, RestDataService>();

Answer 4

我刚刚遇到了这个问题，因为我不小心将 HttpClient 注册到了 interface。

public void ConfigureServices(IServiceCollection services) {
  // !! Wrong, this is done automatically by AddHttpClient<IMyService, MyService>()
  services.AddTransient<IMyService, MyService>();

  // !! There is no suitable constructor for IMyService, since it is an interface.
  services.AddHttpClient<IMyService>();

  // Instead, let AddHttpClient manage your service's lifetime, 
  // and tell it the implementation.
  // It is registered with a Transient lifetime as described below.
  services.AddHttpClient<IMyService, MyService>();
}

重要上下文，来源：https://www.stevejgordon.co.uk/ihttpclientfactory-patterns-using-typed-clients-from-singleton-services

<块引用>

在 ConfigureServices 方法中定义类型化客户端时，类型化服务注册到瞬态范围。这意味着每次需要时，DI 容器都会创建一个新实例。发生这种情况的原因是 HttpClient 实例被注入到类型化的客户端实例中。该 HttpClient 实例的生命周期很短，以便 HttpClientFactory 可以确保释放和回收底层处理程序（和连接）。

找不到类型为'RestDataService'的合适构造函数

4 个答案: