Книга: C# 2008 Programmer

Passing Parameters to Threads

Passing Parameters to Threads

In the past few examples, you've seen how to create a thread using the ThreadStart delegate to point to a method. So far, though, the method that you have been pointing to does not have any parameters:

static void DoSomething() {
 ...
 ...
}

What if the function you want to invoke as a thread has a parameter? In that case, you have two choices:

? Wrap the function inside a class, and pass in the parameter via a property.

? Use the ParameterizedThreadStart delegate instead of the ThreadStart delegate.

Using the same example, the first choice is to wrap the DoSomething() method as a class and then expose a property to take in the parameter value:

class Program {
 static void Main(string[] args) {
  SomeClass sc = new SomeClass();
  sc.msg = "useful";
  Thread t = new Thread(new ThreadStart(sc.DoSomething));
  t.Start();
 }
}
class SomeClass {
 public string msg { get; set; }
 public void DoSomething() {
  try {
   while (true) {
    Console.WriteLine("Doing something...{0}", msg);
   }
  } catch (ThreadAbortException ex) {
   Console.WriteLine(ex.Message);
  } finally {
   //---clean up your resources here---
  }
 }
}

In this example, you create a thread for the DoSomething() method by creating a new instance of the SomeClass class and then passing in the value through the msg property.

For the second choice, you use the ParameterizedThreadStart delegate instead of the ThreadStart delegate. The ParameterizedThreadStart delegate takes a parameter of type object, so if the function that you want to invoke as a thread has a parameter, that parameter must be of type object.

To see how to use the ParameterizedThreadStart delegate, modify the DoSomething() function by adding a parameter:

static void DoSomething(object msg) {
 try {
  while (true) {
   Console.WriteLine("Doing something...{0}", msg);
  }
 } catch (ThreadAbortException ex) {
  Console.WriteLine(ex.Message);
 } finally {
  //---clean up your resources here---
 }
}

To invoke DoSomething() as a thread and pass it a parameter, you use the ParameterizedThreadStart delegate as follows:

static void Main(string[] args) {
 Thread t = new Thread(new ParameterizedThreadStart(DoSomething));
 t.Start("useful");
 Console.WriteLine("Continuing with the execution...");
 ...

The argument to pass to the function is passed in the Start() method.

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