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Multi Threading and forms

Posted on 2006-06-19
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Last Modified: 2010-04-16
Hi Experts,

     I have a form with a text box and a command button.  When the user presses the command button, I want to create two seperate instances of the same class and have them run on a thread of there own.  The threads will each come up with a random number between 1 and 10.  When the threads are done I want the form to take the two randomly generated numbers, add them up, and display the added value in the text box.

Something like this:

Form1.cs:
namespace MyNameSpace
{
           Public Partial Class MyForm : Form
           {
                      MyClass class1 = new MyClass;
                      MyClass class2 = new MyClass;
                     
                      class1.StartThread();
                      class2.StartThread();
           

                      Public void AddThem()
                      {
                                  txtBox.Text=class1.Result+class2.Result;
                      }

           }
}

MyClass.cs:
namespace MyNameSpace
{
           public class MyClass
           {
                      int RandNum;
                     
                      public int Result
                      {
                                 get
                                 {
                                              return RandNum;
                                  }
                                  set
                                  {
                                   }
                       }

                      public void StartThread()
                      {
                                 Thread t = new Thread(new ThreadStart(ThreadJob));
                                 t.IsBackground = true;
                                 t.Start();
                       }

                       private void ThreadJob()
                      {
                                 RandNum=GetRandomNum();
                                 myForm.AddThem();
                       }
}

What I am basically having problems with is how to call a function that only exists in the form's code from the class threads.  I know that in my example I could have a zero value for Class1.Result or Class2.Result depending on which thread finished first, but I am not worried about that for now.  I need the classes to be on their own threads so that the GUI is still functioning while my classes are coming up with the random numbers.  I know that in this example I wouldn't need to use mutliple threads, but this is just an example.  In reality ThreadJob takes about 30 seconds to execute.

Any help would be appreciated,

Thanks,
axnst2
0
Comment
Question by:axnst2
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4 Comments
 

Author Comment

by:axnst2
ID: 16934914
Please also let me know if you think that I am just going about doing this completely the wrong way.

Thanks.
0
 
LVL 48

Accepted Solution

by:
AlexFM earned 2000 total points
ID: 16935137
   public partial class Form1 : Form
    {
        MyClass class1;
        MyClass class2;

        public Form1()
        {
            InitializeComponent();

            class1 = new MyClass();
            class1.OnResultHandler += new ResultHandler(class_OnResultHandler);

            class2 = new MyClass();
            class2.OnResultHandler += new ResultHandler(class_OnResultHandler);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            class1.StartThread();
            class2.StartThread();
        }

        void class_OnResultHandler(int result)
        {
            this.Invoke(new ResultHandler(this.HandleResult), new object[] { result });
        }

        void HandleResult(int result)
        {
            int n = 0;

            try
            {
                n = Int32.Parse(textBox1.Text);
            }
            catch (Exception)
            {
            }

            n += result;

            textBox1.Text = n.ToString();
        }
    }

    public delegate void ResultHandler(int result);

    public class MyClass
    {
        public event ResultHandler OnResultHandler;

        int RandNum;

        public void StartThread()
        {
            Thread t = new Thread(new ThreadStart(ThreadJob));
            t.IsBackground = true;
            t.Start();
        }

        private void ThreadJob()
        {
            RandNum = GetRandomNum();

            if ( OnResultHandler != null )
            {
                OnResultHandler(RandNum);
            }
        }

        int GetRandomNum()
        {
            return 5;
        }
    }
0
 
LVL 48

Expert Comment

by:AlexFM
ID: 16935203
Some explanations: MyClass defines event OnResultHandler which reports to subscriber result of thread calculation.
Form1 creates MyClass instances and subscribes to their OnResultHandler event.
OnResultHandler(RandNum) - this is actually call to class_OnResultHandler function.
class_OnResultHandler function is called in a worker thread context and cannot access directly form controls. It uses Invoke call which calls HandleResult function in the context of main application thread. By the way, using Invoke also solves the problem of thread safety.
Just for fun, it is possible to write one function which calls itself, and remove HandleResult function:

        void class_OnResultHandler(int result)
        {
            if ( this.InvokeRequired )
            {
                this.Invoke(new ResultHandler(this.class_OnResultHandler), new object[] { result });
            }
            else
            {
                int n = 0;

                try
                {
                    n = Int32.Parse(textBox1.Text);
                }
                catch (Exception)
                {
                }

                n += result;

                textBox1.Text = n.ToString();
            }
        }

See also:
http://www.codeproject.com/csharp/workerthread.asp
0
 

Author Comment

by:axnst2
ID: 16935639
Thanks Alex,  That worked great!
0

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