Event getting triggered multiple times on scroll event handler

Question

While I was adding code to scroll event of a panel in c#, I found a strange behavior.

I have added a panel and inside the panel (auto-Scroll = true) there is a groupbox.

As shown below clicking the scroll moves scroll bar to a small distance.

At the same time, when I add a message box in the event to display a notification that a scroll has taken place, multiple message box are popping out.

Why is that?

I have already planned to add some logic when scrolling, but if it occurs multiple times then how it could be possible?

Here is the event handler:

private void panel1_Scroll_1(object sender, ScrollEventArgs e)
{
    MessageBox.Show("ScrollBar is clicked");
}

http://stackoverflow.com/questions/9220691/track-bar-only-fire-event-on-final-value-not-ever-time-value-changes — CharithJ, Jul 29 '15 at 04:49
Similar handling is required. You cannot stop it firing many times. You should handle it appropriately in a similar way that is explained in that thread. — CharithJ, Jul 29 '15 at 04:51
thank you @CharithJ,but one more question..then why does the pic1 showed like that ? — Tharif, Jul 29 '15 at 04:53
Because your event has been executed multiple times while scroll bar poistion is being changed. — CharithJ, Jul 29 '15 at 05:03
but the movement of scroll was limited in first pic ?..If we add some event only it triggers multiple time ? correct me if im wrong.. — Tharif, Jul 29 '15 at 05:05

score 3 · Answer 1 · edited May 23 '17 at 11:51

3

This is just how scroll event works, it fires many times while the panel is scrolling.

Try ScrollEventArgs.Type EndScroll which should be the last scroll event.

  private void panel1_Scroll_1(object sender, ScrollEventArgs e)
    {
        if (e.Type == ScrollEventType.EndScroll)
            MessageBox.Show("ScrollBar is clicked");
    }

If above doesn't help for your case you will need to handle those multiple events by using one of approaches explains in this thread.

edited May 23 '17 at 11:51

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answered Jul 29 '15 at 04:59

CharithJ

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Message box is not displayed here ! – Tharif Jul 29 '15 at 05:06
Did you click or scrolled using mouse? Doesn't it work in both cases? – CharithJ Jul 29 '15 at 05:08
i clicked once..scroll too not popping message box out – Tharif Jul 29 '15 at 05:09
actually i cannot scroll using scroll button in mouse..but can move by dragging scroll bar..but eventually no pop ups – Tharif Jul 29 '15 at 05:13
Put a breakpoint there and see what you get for the e.Type? – – CharithJ Jul 29 '15 at 05:47
e.Type = SmallIncrement – Tharif Jul 29 '15 at 05:48
Theoritically, you should receive many events with SmallIncrements and at the end you should receive EndScroll. This is strange. Btw, what are you tring to do? – CharithJ Jul 29 '15 at 05:49
thank you charith ..i was trying to add some events in scroll..and just tested with a message box which showed me this behavior – Tharif Jul 29 '15 at 05:51

Event getting triggered multiple times on scroll event handler

1 Answers1