Bug 414218

Created attachment 123962 [details]
KConfigDialog vs KPageDialog - demo sources & screenshot

KConfigDialog, unlike KPageDialog, wraps all pages added through its API (i.e. all pages we want to be managed) in QScrollArea. This is something unexpected - either both classes should wrap pages, or none of them. Especially when documentation (and common sense) suggests that KConfigDialog is a KPageDialog with built-in config management.

The dialog with QScrollArea sometimes will not adjust its size to its pages, even when it would be possible. This happens at least when resulting height would be larger than 2/3 of the screen height. In this case scrollbar appears, even when everything would fit without it on window few pixels higher. This is Qt thing, but it does not happen when window min size is in effect, e.g. in KPageDialog.

KDE HIG[1][2] recommends that config dialogs should not be scrollable, and this behavior makes it harder/impossible on smaller resolutions. For example: Konsole configuration dialog is made to fit on 800x600 screen, yet with KConfigDialog scrollbars appeared even on 1366x768 (the scrollbarless window is ~560px high). This has been solved with KPageDialog.

Small demo attached. Please adjust `checkboxesCount` for your resolution.

[1] https://hig.kde.org/components/navigation/dialog.html#behavior
[2] https://hig.kde.org/platform/settings.html?highlight=configuration#appearance (this is for system settings, but regular configuration dialogs should be consistent with it IMO)