Threading with listbox in C#

Question

i am developing a code in which a have to read the data form list box and upload an external file, press a button named Start and with this listbox i am getting an error as shown below.

An unhandled exception of type 'System.InvalidOperationException' occurred in System.Windows.Forms.dll

Additional information: Cross-thread operation not valid: Control 'listBox1' accessed from a thread other than the thread it was created on.

my code is as follows

private void Start_Click(object sender, EventArgs e)
{
 Thread ss = new Thread(Automode);  
 ss.Start(); 
} 

 private void Automode()
    {
        ....
       for (int i = 0; i < listBox1.Items.Count; i++)
        {
            listBox1.SetSelected(i, true);

            string pattern = "[gxyzbcmij][-+]?[0-9]*\\.?[0-9]*";
            string text = listBox1.Text;
            Regex gcode = new Regex(pattern, RegexOptions.IgnoreCase);
            MatchCollection code = gcode.Matches(text);
        }
        .....   
     }

here at listbox.SetSelected command it is giving an exception as shown above. please suggest the alternate ways to write it.

As always, separate the UI code from the business code... Redesign it so that the thread code doesn't access the ListBox or any other control. — H H, Jan 06 '16 at 12:37

score 1 · Answer 1 · edited May 23 '17 at 12:04

1

delegate void SetSelectedCall(int index, bool option);

private void SetSelectedElement(int index, bool option)
{
  if (this.listBox1.InvokeRequired)
  { 
    SetSelectedCall d = new SetSelectedCall(SetSelectedElement);
    this.Invoke(d, new object[] { int index, bool option});
  }
  else
  {
    this.listBox1.SetSelected(index,option);
  }
}

Taken from Cross-thread operation not valid: Control 'textBox1' accessed from a thread other than the thread it was created on and tailored for this question.

edited May 23 '17 at 12:04

Community

1
1

answered Jan 06 '16 at 12:46

Mihai-Daniel Virna

984
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19

This does solve the immediate problem but it does not address the deeper design issues. – H H Jan 06 '16 at 13:38

score 0 · Answer 2 · answered Jan 06 '16 at 12:43

You can't access the listBox1 from a background thread.

If possible, run the code from the function Automode() directly in the Start_Click method. If you must have the code ran in a background thread, I would perhaps suggest something more like a Task, that way you can still perform the action based on passing arguments and awaiting a response. Then you can still listBox1 items as selected.

Threading with listbox in C#

2 Answers2