SCROLLBAR not always giving WM_NOTIFICATION_RELEASED

JanBurg · Feb 24th 2020, 9:51am

Hi,
I'm using a scrollbar to navigate in a larger text file. To avoid excessive CPU load when moving the thumb I want to notify only when the thumb is released (WM_NOTIFICATION_RELEASED). Now I noticed that sometimes the thumb is moved but no notification issued. Isn't it a precondition that the widget has to be clicked to change its value and then is released?

Regards
Jan

SEGGER - Florian · Feb 25th 2020, 9:15am

Hi,

I tried to reproduce the behavior you noticed, but the widget always sent a WM_NOTIFY_PARENT message when releasing the press, and also when releasing outside of the scrollbar window.

Best regards,

Florian

JanBurg · Feb 25th 2020, 12:00pm

Hi Florian,
it does always send a WM_NOTIFY_PARENT, but it is often only a WM_NOTIFICATION_VALUE_CHANGED and not a WM_NOTIFICATION_RELEASED.

Regards

Jan

JanBurg · Mar 3rd 2020, 4:19pm

Hello,
can no one help me in this case? It is confusing for the operator if one moves the scollbar and nothing happens.

Regards
Jan

SEGGER - Florian · Mar 3rd 2020, 4:47pm

Hi,

when the value of the SCROLLBAR changed, the notification code of the WM_NOTIFY_PARENT will be WM_NOTIFICATION_VALUE_CHANGED instead of WM_NOTIFICATION_RELEASED. This is intentional, since its value is what the widget is used for most of the times.

For your purpose, I would just react on the WM_NOTIFICATION_VALUE_CHANGED code. This would make the most sense for scrolling through a text file. When the value changed, you can update your window accordingly, using the new scroll position.

Best regards,

Florian

Share