I cannot get the output parameter when use function import by Entity Framework

Here's my SQL Server stored procedure :

ALTER PROCEDURE [dbo].[SearchUser]
  (@Text NVARCHAR(100),  
   @TotalRows INT = 0 OUTPUT)   
AS
BEGIN 
   SELECT @TotalRows=1000
   SELECT * from Users
END

And my C# code

using (var context = new TestDBEntities())
{
    var outputParameter = new ObjectParameter("TotalRows", typeof(Int32));
    context.SearchUser("", outputParameter);
    Response.Write(outputParameter.Value);
}

However outputParameter.Value always is null.

Could anybody tell me why?

Solution

Output parameters filled by its actual values during the execution of the stored procedure.

But table-valued stored procedure actually get executed only in moment when you're trying to iterate resulting recordset, but not calling a wrapper method.

So, this DOES'T work:

using (var context = new TestDBEntities()) 
{ 
    var outputParameter = new ObjectParameter("TotalRows", typeof(Int32)); 
    context.SearchUser("", outputParameter); 

    // Paremeter value is null, because the stored procedure haven't been executed
    Response.Write(outputParameter.Value); 

}

This DOES:

using (var context = new TestDBEntities()) 
{ 
    var outputParameter = new ObjectParameter("TotalRows", typeof(Int32)); 

    // Procedure does not executes here, we just receive a reference to the output parameter
    var results = context.SearchUser("", outputParameter);

    // Forcing procedure execution
    results.ToList();

    // Parameter has it's actual value
    Response.Write(outputParameter.Value); 

}

When you're working with stored procedures what don't return any recordset, they execute immediately after a method call, so you have actual value in output parameter.