Question

I am studying parallelism and would like to know which way do you recommend for me to access other thead elements, for example, imagima I’ll fill a combobox with some names, query the database I would do in parallel but I could not do a combobox.add (result) from within the task, which way do you recommend me?

a simple example to understand my question:

 private void button1_Click (object sender, EventArgs e)
         {
             Task task = new Task (new Action (Count));
             task.Start ();
         }


         void Count ()
         {
             for (int i = 0; i <99; i + +)
             {
                 Thread.Sleep (1);
                 progressBar1.Value = i;
             }
         }

time to pass the value for the progressbar result in error

Answer 1

You cannot access controls on another thread directly. You must invoke them first. Read this article: http://msdn.microsoft.com/en-us/library/ms171728.aspx

This is about what is would look like if you took the article and translated it for your own use: (NOT TESTED)

        delegate void SetProgressBarCallback();

        private void SetProgressBar()
        {
            // InvokeRequired required compares the thread ID of the
            // calling thread to the thread ID of the creating thread.
            // If these threads are different, it returns true.
            if (this.progressBar1.InvokeRequired)
            {   
                SetProgressBarCallback d = new SettProgressBarCallback(SetProgressBar);
                this.Invoke(d);         
            }
            else
            {
                for(int i=0; i<99; i++)
                {
                     Thread.Sleep(1);
                     progressBar1.Value = i;
                 }
            }
        }