Question

EDIT: It is not a listbox. My mistake. It is a list view.

I have a list view control that’s driving me nuts. It is a multi-select list box, so if the user selects 5000 rows, then de-selects them by selecting a single row, the SelectedIndexChanged fires 5001 times. This causes my app to hang.

I’m trying to use threads to count the number of times that the event WOULD have fired, and then letting the last iteration do all the actual work.

Here’s the code I started with. The big catch: I need the ‘do fancy calculations’ to be in the same thread as the calling events due to items out of my control.

EDIT: I know that this code doesn’t work. The Join() blocks the current thread which negates the entire purpose of creating the thread. My question is : How do I do something LIKE this.

My biggest problem isn’t creating the thread. It’s that my ‘do fancy’ has to be in the same thread.

    void IncrPaintQueue()     {         PaintQueue++;         Thread.Sleep(100);     }      int PaintQueue = 0;      private void SegmentList_SelectedIndexChanged(object sender, EventArgs e)     {         // We need to know how many threads this may possibly spawn.         int MyQueue = PaintQueue;          // Start a thread to increment the counter.         Thread Th = new Thread(IncrPaintQueue);         Th.IsBackground = true;         Th.Start();         Th.Join();          // if I'm not the last thread, then just exit.          // The last thread will do the right calculations.         if (MyQueue != PaintQueue - 1)             return;          // Reset the PaintQueue counter.         PaintQueue = 0;          // ... do fancy calculations here...     } 

Answer 1

I remember solving this issue before:

A better way perhaps for you would be to put a minimal delay in your ItemSelectionChange Handler. Say — 50ms. Use a timer, Once the selection changes, restart the timer. If the selection changed more than once within the delay period, then the original is ignored, but after the delay has expired, the logic is executed.

Like this:

public class SelectionEndListView : ListView { private System.Windows.Forms.Timer m_timer; private const int SELECTION_DELAY = 50;  public SelectionEndListView() {    m_timer = new Timer();    m_timer.Interval = SELECTION_DELAY;    m_timer.Tick += new EventHandler(m_timer_Tick); }  protected override void OnSelectedIndexChanged(EventArgs e) {    base.OnSelectedIndexChanged(e);     // restart delay timer    m_timer.Stop();    m_timer.Start(); }  private void m_timer_Tick(object sender, EventArgs e) {    m_timer.Stop();     // Perform selection end logic.    Console.WriteLine('Selection Has Ended'); } }