Question

Please let me know why ParameterizedThreadStart class only allow method which only System.object argument type contain.

public class MainThreadTest
{
    public static void Main(string[] args)
    {
        Thread T = new Thread(new ParameterizedThreadStart(DisplayYOrX));
        T.Start("X");

        DisplayYOrX("Y");
    }

    static void DisplayYOrX(object outValue)
    {
        string Parameter = (string)outValue;

        for(int i=0; i<10; i++)
            Console.Write(Parameter);
    }
}

Why I would like to know about that is I do not want to use type cast syntax again.

string Parameter = (string)outValue;

Answer 1

The reason for the limitation is that ThreadStart isn’t a generic delegate and hence it’s only capable of passing an object around. This is easy enough to work around though by using a lambda where you directly pass the value.

public static void Main(string[] args) {
  ThreadStart start = () => { 
    DisplayYOrX("X");
  };
  Thread t = new Thread(start);
  t.Start();

  ...
}

static void DisplayYOrX(string outValue) {
  ...
}

Version for C# 2.0

public static void Main(string[] args) {
  ThreadStart start = delegate { 
    DisplayYOrX("X");
  };
  Thread t = new Thread(start);
  t.Start();

  ...
}