Access ListBox.SelectedItems from another thread

Question

I have ListBox called lstProductGroups.

On a simple Windows Form, a method called GetGroups gives me string groups selected by the user like Cars, Bikes etc.

public List<string> GetGroups()
{
    List<string> prodGroups = (from object item in lstProductGroups.SelectedItems select item.ToString()).ToList();

    return prodGroups;
}

But if I try to access same method from another thread I get all items in my list called System.Data.DataRowView.

I even tried it in a foreach loop with BeginInvoke, but the item.ToString() always returns System.Data.DataRowView.

I am new to Winforms with threading. What am I doing wrong?

What are you using to facilitate threading; BackgroundWorker, Thread, Task? — MoonKnight
– MoonKnight, Commented Mar 27, 2012 at 10:29
Did you try to call GetGroups() method from the other thread with Invoke()? It should return the right list. — Adriano Repetti
– Adriano Repetti, Commented Mar 27, 2012 at 10:33
Third party API's event that I am subscribed to. I do not know their internal implementation. But any UI update code from the event method raised Cross-thread operation not valid: Control accessed from a thread other than the thread it was created on. — One-One
– One-One, Commented Mar 27, 2012 at 10:34

ionden · Accepted Answer · 2012-03-27 10:42:11Z

1

First declare a delegate:

delegate List<string> GetItemsDlg();

Change your method like this:

List<string> GetGroups() {
    if (lstProductGroups.InvokeRequired) {
        var dlg = new GetItemsDlg(GetGroups);
        return lstProductGroups.Invoke(dlg) as List<string>;
    }
    List<string> prodGroups = (from object item in lstProductGroups.SelectedItems select item.ToString()).ToList();

    return prodGroups;

}

Call your method:

List<string> items = GetGroups();

answered Mar 27, 2012 at 10:42

ionden

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Comments

Yuki Kutsuya · Accepted Answer · 2012-03-27 10:38:50Z

0

How about invoke:

Invoke((MethodInvoker) delegate
                               {
                                 ...
                               }

answered Mar 27, 2012 at 10:38

Yuki Kutsuya

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