How to make T parameter available

Question

I am writing an asynchronous class to simplify function operation. Below is my code:

using System;

namespace AsyncLibery
{
public class AsyncLibery
{
    delegate void Exec(); // No input parameter, no return value
    delegate void ExecWithParams<T>(T T1); //One input parameter, no return value
    delegate void ExecWithParams<T1, T2>(T1 t1,T2 t2); //Two input parameters, no return value 
    delegate void ExecWithParams<T1, T2, T3>(T1 t1, T2 t2, T3 t3);//Three input parameters, no return value
    delegate void ExecWithParams<T1, T2, T3, T4>(T1 t1, T2 t2, T3 t3, T4 t4);//Four input parameters,no return value

    delegate T  ExecWithReturnType<T>(); //No input parameter, one return value
    delegate T2 ExecWithReturnType<T1, T2>(T1 t1); //One input parameter, one return value
    delegate T3 ExecWithReturnType<T1, T2, T3>(T1 t1, T2 t2);//Two input parameters, one return value
    delegate T4 ExecWithReturnType<T1, T2, T3, T4>(T1 t1, T2 t2, T3 t3);//Three input parameters, one return value
    delegate T5 ExecWithReturnType<T1, T2, T3, T4, T5>(T1 t1, T2 t2, T3 t3, T4 t4);// Four input parameters, one return value.

    #region no input parameter, no return value
    public void BeginInvokeEx(Action actionFunction)
    {
        Exec exec = new Exec(actionFunction);
        exec.BeginInvoke(new AsyncCallback(EndInvokeEx), exec);
    }

    private void EndInvokeEx(IAsyncResult iar)
    {
        Exec exec = (Exec)iar.AsyncState;
        exec.EndInvoke(iar);
    }
    #endregion

    #region one input parameter, no return value
    public void BeginInvokeEx<T>(Action<T> actionFunction,T T1)
    {
        ExecWithParams<T> exec = new ExecWithParams<T>(actionFunction);
        exec.BeginInvoke(T1, new AsyncCallback(EndInvokeEx1), exec);
    }

    private void EndInvokeEx1(IAsyncResult iar)
    {
        ExecWithParams<T> exec = (ExecWithParams<T>)iar.AsyncState;
        exec.EndInvoke(iar);
    }
    #endregion
}
}

When I complied the code, it throws me an exception like "The type or namespace name 'T' could not be found (are you missing a using directive or an assembly reference?)", the exception is appeared at below code :

ExecWithParams<T> exec = (ExecWithParams<T>)iar.AsyncState;

I know that we must refer T parameter the specific type like int or string or anything else. But who can help me without modifying the T parameter? is there any good method to deal with it? thx.

Answer 1

Make EndInvokeEx1 generic:

private void EndInvokeEx1<T>(IAsyncResult iar)
{
    ExecWithParams<T> exec = (ExecWithParams<T>)iar.AsyncState;
    exec.EndInvoke(iar);
}

And change your BeginInvokeEx accordingly:

public void BeginInvokeEx<T>(Action<T> actionFunction,T T1)
{
    ExecWithParams<T> exec = new ExecWithParams<T>(actionFunction);
    exec.BeginInvoke(T1, new AsyncCallback(EndInvokeEx1<T>), exec);
}

Answer 2

You haven't defined what T is. You need to either have a generic parameter on the method EndInvokeEx1 such that it becomes EndInvokeEx<T>, where you can then pass T to the cast. Otherwise, it will need to be defined in the class declaration, so your class declaration becomes public class AsyncLibrary<T>. Otherwise, the compiler won't know what T is meant to represent.