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Thread: QT Widgets, Touch screen, Ubuntu 22.04, On-Screen keyboard issues

  1. #1
    Join Date
    Nov 2016
    Florida, US
    Qt products

    Default Re: QT Widgets, Touch screen, Ubuntu 22.04, On-Screen keyboard issues

    I am just clueless where to start looking for this, and apologies as it a bit complicated.

    I use QT (6.4.0) on Ubuntu 22.04, on an embedded Windows system inside a player piano with a touch screen display (only, no keyboard). Wayland.

    Under accessibility I turn on on the on-screen keyboard. As an example, when looking at the music library, if they click a search field and start typing, it filters a table widget.

    Mostly it works. Sometimes when you type on the keyboard no characters appear. What's more weird, if there are already characters in the field, the backspace key DOES work. But no matter what keys or shift or other I hit, nothing appears (and indeed nothing is going in, this is not a display problem, I can tell because no filtering occurs).

    This happens on multiple fields; once it gets into this state, I cannot touch-type into any field. Some fields have events coded (e.g. the search updates on keystroke) but others do not have my code for each character, so I do not think it is me processing characters incorrectly as some cases I am not processing them at all.

    Restarting the application restores normal behavior. I have not noticed this on any other application (but to be fair is a pretty dedicated application so there is not much opportunity)

    This happens after "a while". Sometimes a minute or two, sometimes days of use. I can find no pattern. I cannot reproduce it on demand, but it will happen inevitably if I wait long enough.

    This may well be a ubuntu problem. But it seems to have started after I rebuilt the application in Qt6 and moved to a new computer and from 20.04 to 22.04 (i.e. a lot of things changed at once).

    To be clear -- the keyboard opens, the keyboard responds (e.g. shift key changes the keys), all normal touch operations continue to work, I just cannot get the on-screen keyboard to enter characters into QT widgets (but again, backspace works!).

    Any ideas? What can I be missing?

    Or what I can do to track it down?


    PS. I'm not sure relevant, it could be luck the draw, but I have yet to be able to reproduce this at all on an xrdp session from the same computer that I normally use for debugging, it seems to only happen on the real, actual HDMI/USB connected touch screen.

    (An hour later)

    Update: I was wrong, this DOES happen to other applications. I thought I had test that, but had it just fail, closed the QT app (necessary as it is full screen), opened terminal and same situation -- could not enter text from the keyboard. I did verify before closing the QT app that the backspace key DOES work, but no other keys apparently.

    This leads me to the conclusion though that this must be a Ubuntu not QT problem.
    Last edited by Linwood; 25th January 2023 at 20:06.

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