我如何手动解析一个类型使用ASP。NET核心MVC内置依赖注入框架?
设置容器非常简单:
public void ConfigureServices(IServiceCollection services)
{
// ...
services.AddTransient<ISomeService, SomeConcreteService>();
}
但是如何在不执行注入的情况下解析ISomeService呢?例如，我想这样做:
ISomeService service = services.Resolve<ISomeService>();
在IServiceCollection中没有这样的方法。
当前回答
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc();
services.AddDbContext<ConfigurationRepository>(options =>
options.UseSqlServer(Configuration.GetConnectionString("SqlConnectionString")));
services.AddScoped<IConfigurationBL, ConfigurationBL>();
services.AddScoped<IConfigurationRepository, ConfigurationRepository>();
}
其他回答
如果你用模板生成一个应用程序，你会在Startup类上有这样的东西:
public void ConfigureServices(IServiceCollection services)
{
// Add framework services.
services.AddApplicationInsightsTelemetry(Configuration);
services.AddMvc();
}
然后你可以在那里添加依赖项，例如:
services.AddTransient<ITestService, TestService>();
如果你想在你的控制器上访问ITestService，你可以在构造函数上添加IServiceProvider，它将被注入:
public HomeController(IServiceProvider serviceProvider)
然后你可以解析你添加的服务:
var service = serviceProvider.GetService<ITestService>();
注意，要使用通用版本，你必须包含扩展名的命名空间:
using Microsoft.Extensions.DependencyInjection;
ITestService.cs
public interface ITestService
{
int GenerateRandom();
}
TestService.cs
public class TestService : ITestService
{
public int GenerateRandom()
{
return 4;
}
}
Startup.cs (ConfigureServices)
public void ConfigureServices(IServiceCollection services)
{
services.AddApplicationInsightsTelemetry(Configuration);
services.AddMvc();
services.AddTransient<ITestService, TestService>();
}
HomeController.cs
using Microsoft.Extensions.DependencyInjection;
namespace Core.Controllers
{
public class HomeController : Controller
{
public HomeController(IServiceProvider serviceProvider)
{
var service = serviceProvider.GetService<ITestService>();
int rnd = service.GenerateRandom();
}
public void ConfigureServices(IServiceCollection services)
{
services.AddMvc();
services.AddDbContext<ConfigurationRepository>(options =>
options.UseSqlServer(Configuration.GetConnectionString("SqlConnectionString")));
services.AddScoped<IConfigurationBL, ConfigurationBL>();
services.AddScoped<IConfigurationRepository, ConfigurationRepository>();
}
您可以使用IApplicationBuilder实例以这种方式注入依赖项
public void Configure(IApplicationBuilder app)
{
//---------- Your code
using (var serviceScope = app.ApplicationServices.GetRequiredService<IServiceScopeFactory>().CreateScope())
{
var resultLogic = serviceScope.ServiceProvider.GetService<IResultLogic>();
resultLogic.YourMethod();
}
//---------- Your code
}
如果您只是为了将一个依赖项传递给正在注册的另一个依赖项的构造函数而解析它，那么您可以这样做。
假设您有一个接受字符串和ISomeService的服务。
public class AnotherService : IAnotherService
{
public AnotherService(ISomeService someService, string serviceUrl)
{
...
}
}
当你在Startup.cs中注册这个时，你需要这样做:
services.AddScoped<IAnotherService>(ctx =>
new AnotherService(ctx.GetService<ISomeService>(), "https://someservice.com/")
);
我知道这是一个老问题，但我很惊讶，一个相当明显和恶心的黑客没有在这里。
您可以利用定义自己的ctor函数的能力，在定义服务时从服务中获取必要的值……显然，每次请求服务时都会运行此服务，除非您在利用ctor的第一个构造中显式地删除/清除并重新添加此服务的定义。
这种方法的优点是不需要您在服务配置期间构建或使用服务树。您仍然在定义如何配置服务。
public void ConfigureServices(IServiceCollection services)
{
//Prey this doesn't get GC'd or promote to a static class var
string? somevalue = null;
services.AddSingleton<IServiceINeedToUse, ServiceINeedToUse>(scope => {
//create service you need
var service = new ServiceINeedToUse(scope.GetService<IDependantService>())
//get the values you need
somevalue = somevalue ?? service.MyDirtyHack();
//return the instance
return service;
});
services.AddTransient<IOtherService, OtherService>(scope => {
//Explicitly ensuring the ctor function above is called, and also showcasing why this is an anti-pattern.
scope.GetService<IServiceINeedToUse>();
//TODO: Clean up both the IServiceINeedToUse and IOtherService configuration here, then somehow rebuild the service tree.
//Wow!
return new OtherService(somevalue);
});
}
修复这个模式的方法是让OtherService显式依赖于IServiceINeedToUse，而不是隐式依赖于它或它的方法的返回值…或者以其他方式显式地解决依赖关系。
