C＃Func <>委托属性设置器问题

Question

I am trying to return an object of type IDocumentTemplateProvider using a delegate as below:

public static class DocumentTemplateProvider
{
    private static Func<IDocumentTemplateProvider> _docTemplateProvider;

    public static void SetdocTemplateProvider(Func<IDocumentTemplateProvider> docTemplateProvider)
    {
        _docTemplateProvider = docTemplateProvider;
    }

    public static void SetDocTemplateProvider<T>() where T : IDocumentTemplateProvider, new()
    {
        _docTemplateProvider = () => new T();
    }

    public static IDocumentTemplateProvider TemplateProvider
    {
        get { return _docTemplateProvider(); }
    }
}

However when I'm calling it using:

private static readonly IDocumentTemplateProvider _template = DocumentTemplateProvider.TemplateProvider;

_template is always null. I'm fairly new to C# Func<> delegates so i can't bloody see what I'm doing wrong. Can someone point me to the right direction?

Thanks

UPDATE: To clear ant confusion i've added the full code where _template is initialized and used as is:

 public class DocumentModule : IHttpModule
{
        private static readonly IDocumentTemplateProvider _template = DocumentTemplateProvider.TemplateProvider;

        public void Init(HttpApplication context)
        {
            context.BeginRequest += OnBeginRequest;
            context.EndRequest += OnEndRequest;
        }      

        public void Init(HttpApplication context)
        {
            context.BeginRequest += OnBeginRequest;
            context.EndRequest += OnEndRequest;
        }

        private void OnBeginRequest(object sender, EventArgs eventArgs)
        {
            _template.SetProvider();
        }

        private void OnEndRequest(object sender, EventArgs e)
        {
            _template.Finalize();
        }        

        public void Dispose()
        {
        }
}

Answer 1

It is null because it is has never been set. You have two Void methods that set the _docTemplateProvider variable, so you need to call them first, like the example code below

class Program
{
    private static void Main()
    {
        DocumentTemplateProvider.SetDocTemplateProvider<Test>();
        //OR
        DocumentTemplateProvider.SetdocTemplateProvider(() => new Test());

        IDocumentTemplateProvider _template = DocumentTemplateProvider.TemplateProvider;

        Console.ReadLine();
    }

    public static class DocumentTemplateProvider
    {
        private static Func<IDocumentTemplateProvider> _docTemplateProvider;

        public static void SetdocTemplateProvider(Func<IDocumentTemplateProvider> docTemplateProvider)
        {
            _docTemplateProvider = docTemplateProvider;
        }

        public static void SetDocTemplateProvider<T>() where T : IDocumentTemplateProvider, new()
        {
            _docTemplateProvider = () => new T();
        }

        public static IDocumentTemplateProvider TemplateProvider
        {
            get { return _docTemplateProvider(); }
        }
    }
}

internal interface IDocumentTemplateProvider
{
}

public class Test : IDocumentTemplateProvider
{
}