HttpContextAccessor、IPrincipal 和 ServiceCollection

Question

有没有办法实现下一个行为？

public static void Configure(IServiceCollection services) {
    services.AddScoped(typeof(Func<IPrincipal>), ???);
    services.AddInstance(typeof(Func<IPrincipal>), ???);
}

1.不起作用：

Func<IServiceProvider, IPrincipal> getPrincipal = 
    (sp) => sp.GetService<IHttpContextAccessor>().HttpContext.User;

services.AddScoped(
    typeof(Func<IPrincipal>), 
    getPrincipal);  

2.不起作用：

var builder = services.BuildServiceProvider();

services.AddInstance(
    typeof(Func<IPrincipal>),
    builder.GetService<IHttpContextAccessor>().HttpContext.User);

Answer 1

Func<IServiceProvider, IPrincipal> getPrincipal = 
    (sp) => sp.GetService<IHttpContextAccessor>().HttpContext.User;

services.AddScoped(
    typeof(Func<IPrincipal>), 
    getPrincipal); 

您正在尝试解析委托，但我假设您想要解析 IPrincipal。我假设您的服务可能看起来像这样

public class MyService : IMyService 
{
    public MyService(IPrincipal principal) 
    {
        ...
    }
}

如果是这样，那么您的注册是错误的。您正在注册 Func<IPrincipal>，但期待未注册的 IPrincipal。

您应该为IPrincipal 注册工厂或（不太推荐恕我直言）将Func<IPrincipal> 注入您的服务。

Func<IServiceProvider, IPrincipal> getPrincipal = 
    (sp) => sp.GetService<IHttpContextAccessor>().HttpContext.User;

services.AddScoped<IPrincipal>(getPrincipal); 

或更短的

services.AddScoped<IPrincipal>(
    (sp) => sp.GetService<IHttpContextAccessor>().HttpContext.User
); 

或

public class MyService : IMyService 
{
    priate IPrincipal principal;
    public MyService(Func<IPrincipal> principalFactory) 
    {
        this.principal = principalFactory();
    }
}

Answer 2

工作解决方案：

Func<IServiceProvider, IPrincipal> getPrincipal = 
    (sp) => sp.GetService<IHttpContextAccessor>().HttpContext.User;

services.AddScoped(typeof(Func<IPrincipal>), sp => {
    Func<IPrincipal> func = () => {
        return getPrincipal(sp);
    };

    return func;
});