Improve QListView scroll bar calculation.

When both scroll bar's policies are set to ScrollBarAsNeeded, make sure
the scroll bars are shown if needed and not show if not. Even the corner
case, where one scroll bar's visibility depends on the other, is handled
properly.

Task-number: QTBUG-45470
Change-Id: I11d6ccf7c0b51644a5ce2d5c3fc59e2e4812755d
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
Reviewed-by: Thorbjørn Lund Martsum <tmartsum@gmail.com>
Reviewed-by: Thorbjørn Lindeijer <bjorn@lindeijer.nl>

1 files changed, 22 insertions, 4 deletions

diff --git a/src/widgets/itemviews/qlistview.cpp b/src/widgets/itemviews/qlistview.cpp
index b7a4ec3925..f3fd3e75a1 100644
--- a/src/widgets/itemviews/qlistview.cpp
+++ b/src/widgets/itemviews/qlistview.cpp
@@ -1846,8 +1846,17 @@ void QCommonListViewBase::updateHorizontalScrollBar(const QSize &step)
     const bool bothScrollBarsAuto = qq->verticalScrollBarPolicy() == Qt::ScrollBarAsNeeded &&
                                     qq->horizontalScrollBarPolicy() == Qt::ScrollBarAsNeeded;
 
-    if (bothScrollBarsAuto && contentsSize.width() - qq->verticalScrollBar()->width() <= viewport()->width()
-                           && contentsSize.height() - qq->horizontalScrollBar()->height() <= viewport()->height()) {
+    const QSize viewportSize(viewport()->width() + (qq->verticalScrollBar()->maximum() > 0 ? qq->verticalScrollBar()->width() : 0),
+                             viewport()->height() + (qq->horizontalScrollBar()->maximum() > 0 ? qq->horizontalScrollBar()->height() : 0));
+
+    bool verticalWantsToShow = contentsSize.height() > viewportSize.height();
+    bool horizontalWantsToShow;
+    if (verticalWantsToShow)
+        horizontalWantsToShow = contentsSize.width() > viewportSize.width() - qq->verticalScrollBar()->width();
+    else
+        horizontalWantsToShow = contentsSize.width() > viewportSize.width();
+
+    if (bothScrollBarsAuto && !horizontalWantsToShow) {
         // break the infinite loop described above by setting the range to 0, 0.
         // QAbstractScrollArea will then hide the scroll bar for us
         horizontalScrollBar()->setRange(0, 0);
@@ -1868,8 +1877,17 @@ void QCommonListViewBase::updateVerticalScrollBar(const QSize &step)
     const bool bothScrollBarsAuto = qq->verticalScrollBarPolicy() == Qt::ScrollBarAsNeeded &&
                                     qq->horizontalScrollBarPolicy() == Qt::ScrollBarAsNeeded;
 
-    if (bothScrollBarsAuto && contentsSize.width() - qq->verticalScrollBar()->width() <= viewport()->width()
-                           && contentsSize.height() - qq->horizontalScrollBar()->height() <= viewport()->height()) {
+    const QSize viewportSize(viewport()->width() + (qq->verticalScrollBar()->maximum() > 0 ? qq->verticalScrollBar()->width() : 0),
+                             viewport()->height() + (qq->horizontalScrollBar()->maximum() > 0 ? qq->horizontalScrollBar()->height() : 0));
+
+    bool horizontalWantsToShow = contentsSize.width() > viewportSize.width();
+    bool verticalWantsToShow;
+    if (horizontalWantsToShow)
+        verticalWantsToShow = contentsSize.height() > viewportSize.height() - qq->horizontalScrollBar()->height();
+    else
+        verticalWantsToShow = contentsSize.height() > viewportSize.height();
+
+    if (bothScrollBarsAuto && !verticalWantsToShow) {
         // break the infinite loop described above by setting the range to 0, 0.
         // QAbstractScrollArea will then hide the scroll bar for us
         verticalScrollBar()->setRange(0, 0);