asp.net-core – 如何在中间件类中访问IHostingEnvironment

例如,在我下面的课程中,我认为我可以将IHostingEnvironment注入contstructor,但它始终为null.关于如何访问IHostingEnvironment的任何其他想法？

public class ForceHttps {
    private readonly RequestDelegate _next;
    private readonly IHostingEnvironment _env;

    /// <summary>
    /// This approach to getting access to IHostingEnvironment 
    /// doesn't work.  It's always null
    /// </summary>
    /// <param name="next"></param>
    /// <param name="env"></param>
    public ForceHttps(RequestDelegate next,IHostingEnvironment env) {
        _next = next;
    }


    public async Task Invoke(HttpContext context) {
        string sslPort = "";
        HttpRequest request = context.Request;


        if(_env.IsDevelopment()) {
            sslPort = ":44376";
        }

        if(request.IsHttps == false) {
            context.Response.Redirect("https://" + request.Host + sslPort + request.Path);
        }

        await _next.Invoke(context);

    }
}