Spinbox arrow size on small mobile screens
I know that the size/font of a spinbox or checkbox can easily be increased, but that doesn't help much if the user can't click on one distinct arrow, or on one distinct box. Is there any way to make these characteristics bigger, such that it's easier to use applications that rely heavily on spinboxes or checkboxes?
My advice: don't use the widget at all in a mobile, touch-driven environment. There are better ways of dealing with inputting numbers in such environments. As you found out, the buttons are too small to be of use.
In the past, I made a widget that rendered the buttons to the left and right of the line edit, taking the whole height of the line edit. That worked, but did not look all that elegant. On current mobile platforms, you often see that you get a specialized overlay that allows easy input for the field.