Fix slow scrolling in dock panels

Commit f688bcd1f1 fixed slow scrolling with xf86-input-libinput on DolphinView.

However the commit also exposed a bug in the Dolphin scrolling
algorithm, which was previously hidden. This resulted in slow
scrolling in dock panels (Places and Folders), with both
xf86-input-evdev and xf86-input-libinput drivers, as well as libinput on
Wayland.

KItemListContainer::updateScrollOffsetScrollBar() relied on the view's
itemSize() method to compute the scrollbar's singleStep, but this QSize
was invalid for the dock panels' views.

We use a new itemSizeHint() method instead, which is always valid and
also adapts to the current icon size set in the view.

BUG: 365968
FIXED-IN: 16.12.0
REVIEW: 129409

1 files changed, 1 insertions, 1 deletions

diff --git a/src/kitemviews/kitemlistcontainer.cpp b/src/kitemviews/kitemlistcontainer.cpp
index 6974ebb48..6a0c5756c 100644
--- a/src/kitemviews/kitemlistcontainer.cpp
+++ b/src/kitemviews/kitemlistcontainer.cpp
@@ -265,7 +265,7 @@ void KItemListContainer::updateScrollOffsetScrollBar()
     if (view->scrollOrientation() == Qt::Vertical) {
         smoothScroller = m_verticalSmoothScroller;
         scrollOffsetScrollBar = verticalScrollBar();
-        singleStep = view->itemSize().height();
+        singleStep = view->itemSizeHint().height();
         // We cannot use view->size().height() because this height might
         // include the header widget, which is not part of the scrolled area.
         pageStep = view->verticalPageStep();