C# Generic question

Question

I have this function

public DataSet Fetch(string EntityName, ObjectParameter[] parameters, int pagesize, int pageindex)
    {
        Assembly asm = Assembly.Load("NCR.WO.PLU.ItemEDM");
        Type _type = asm.GetTypes().Where(t => t.Name.Equals(EntityName)).ToList().FirstOrDefault();

        object obj = Activator.CreateInstance(_type);

        return DataPortalFetch<???>(parameters, pagesize, pageindex);
    }

how do i pass that _type to the generic part??

Answer 1

You have to call the method using reflection. Generics are designed for types which are known at compile-time; you don't know the type at compile-time, therefore you have to jump through some hoops. It'll be something along the lines of:

MethodInfo method = typeof(WhateverClass).GetMethod("DataPortalFetch");
MethodInfo constructed = method.MakeGenericMethod(new Type[] { _type });
return constructed.Invoke(this, new object[] {parameters, pagesize, pageindex});

The details will depend on whether it's an instance method or a static method, whether it's public or private etc - but the basics are:

• Get the generic method definition
• Construct a method with the right type (effectively: pass the type argument)
• Invoke that constructed method

You may want to cache the generic method definition in a static readonly field, btw - it's reusable.