[Development] Issues with QApplication::startDragDistance

Jeremias Bosch jeremias.bosch at basyskom.com
Thu Nov 13 11:11:36 CET 2014

Dear all,
I was looking into deploying a simple QML App on a wide range of 
devices. The App consists basically of two QML Lists which are used for 
horizontal and vertical page navigation. The ranges of Display DPI 
differ a lot between those devices.

Now there are two issues I ran into.

 1. On High DPI cases the sensitivity of the lists is very high,
    basically touching the screen is already registered as a drag and
    pressing buttons is pretty hard. On Low DPI its fine. Of course you
    can tweak the startDragDistance with
    QApplication::startDragDistance, or the corresponding value in your
    Platform Style. However, this would mean that you need to adjust for
    each target device to get the expected behavior, which might not be
    possible and preferable - I think that the default value should
    respect the screen DPI.
 2. I would like to have the vertical page navigation list to be less
    sensitive than the horizontal page navigation list and the
    horizontal page navigation list even less sensitive than all other
    "normal" content lists.
    I couldn't find a way to adjust the sensitivity on a case by case
    situation. All I found was a feature request
    https://bugreports.qt-project.org/browse/QTBUG-18792, but it was
    closed invalid back in 2011, without any comment.
    Maybe I overlook a feature and this is already possible?

What do you think?

  * Wouldn't it make sense to make the default start drag distance
    respecting screen dpi?
  * What do you think about to add a property on the QML Flickable in
    order to customize startDragDistance for this one QML Flickable? Are
    there any concerns about having such a property?

Thanks for your opinion,

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