asp .net core 不使用构造函数获得注入的对象

使用asp .net core 2.1使用自带的依赖注入，自带的依赖注入是构造函数注入。有些情况，构造函数注入并不能满足需求，所以需要使用其他方法获取指定实例。

    
public interface IEngine
 {
        /// <summary>
        /// 类型构建
        /// </summary>
        /// <param name="type"></param>
        /// <returns></returns>
        object Resolve(Type type);
}

    
public class GetEngine: IEngine
{
        private IServiceProvider _serviceProvider;
        public GetEngine(IServiceProvider serviceProvider)
        {
            this._serviceProvider = serviceProvider;
        }

        /// <summary>
        /// 类型构建
        /// </summary>
        /// <param name="type"></param>
        /// <returns></returns>
        public object Resolve(Type type)
        {
            return _serviceProvider.GetService(type);
        }
}


public class EnginContext
 {
        private static IEngine _engine;

        [MethodImpl(MethodImplOptions.Synchronized)]
        public static IEngine Initialize(IEngine engine)
        {
            if (_engine == null)
                _engine = engine;
            return _engine;
        }

        public static IEngine Current
        {
            get
            {
                return _engine;
            }
        }
 }

需要在 Startup.cs 的 Configure方法中调用,如下：


EnginContext.Initialize(new GetEngine(app.ApplicationServices));

完整示例如下：


public void Configure(IApplicationBuilder app, IHostingEnvironment env)
 {
            if (env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            else
            {
                app.UseExceptionHandler("/Home/Error");
                app.UseHsts();
            }

            EnginContext.Initialize(new GetEngine(app.ApplicationServices));

            app.UseHttpsRedirection();
            app.UseStaticFiles();
            app.UseCookiePolicy();
            app.UseMvc(routes =>
            {
                routes.MapRoute(
                    name: "default",
                    template: "{controller=Home}/{action=Index}/{id?}");
            });
  }

新增一个类Information进行测试，如下：


    public class Information
    {
        private string Name => "Dot Net Core";
        public string GetName()
        {
            return $"你好!{Name}";
        }
    }

在ConfigureServices方法中将新增的类进行注入。


        
        public void ConfigureServices(IServiceCollection services)
        {
            services.Configure<CookiePolicyOptions>(options =>
            {
                // This lambda determines whether user consent for non-essential cookies is needed for a given request.
                options.CheckConsentNeeded = context => true;
                options.MinimumSameSitePolicy = SameSiteMode.None;
            });

            services.AddTransient<Information>();
            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
        }

通过以下方式进行获取已经注入的对象。


EnginContext.Current.Resolve(typeof(Information));

使用示例如下：


        public IActionResult About()
        {
            ViewData["Message"] = "Your application description page.";
            var info= EnginContext.Current.Resolve(typeof(Information)) as Information;
            ViewData["Message"] = info.GetName();
            return View();
        }