Cross thread problem?

Question

My error

Cross-thread operation not valid: Control \'MailTree\' accessed from a thread other than the thread it was created on.

Answer 1

You cannot directly access a control from another thread, you will have to invoke it.

private delegate void ControlCallback(string s);

public void CallControlMethod(string text)
{
    if (control.InvokeRequired)
    {
        ControlCallback call = new ControlCallback((s) =>
        {
            // do control stuff
        });
        control.Invoke(call, new object[] { text });
    }
    else
    {
        // do control stuff
    }
}

Answer 2

you can't access the UI on a different thread than what it was created on. From inside your secondary thread (the one that runs your callback handler) you will need to call Form.BeginInvoke to register a method that will be run on the UI thread. From that method you can update your UI controls

Answer 3

I think AddMesToMailList() is trying to modify the view elements but it is on a wrong thread.

Try something like this

void AddMesToMailList()
{
    if (this.InvokeRequired)
    {
         this.BeginInvoke(new Action(AddMesToMailList));
         return;
    }

    // do stuff that original  AddMesToMailList() did.
}

EDIT: SaveMail is a little complicated as it has a return value but you can try this

public int SaveMail(ImapX.Message mess)
{
     if(this.InvokeRequired)
     {
            return (int) this.Invoke(
                   new Func<ImapX.Message, int>( m => SaveMail(mess)) );
     }
     else
     {

        if (!File.Exists(@"D:\" + Username + "\\" + MailTree.SelectedNode.Text + "\\" + mes.MessageUid.ToString() + ".eml"))
        {
            mess.Process();
            mess.SaveAsEmlToFile(@"D:\" + Username + "\\" + MailTree.SelectedNode.Text + "\\", mes.MessageUid.ToString());   //Store messages to a Location 

        }
       // mes.MessageUid=mess.MessageUid;
        return 1;  

     }



}