Add SH_ItemView_ScrollMode style hint and use it in QMacStyle

On OS X, the default scrolling mode of item views should be
per pixel instead of per item. We enforce this through a new
style hint. On all other platforms, the behavior remains the
same.

It's still possible to override the style hint by using the
regular scroll mode setters. Any subsequent style change will
result in a no-op once the setters have been called and until
the properties are reset.

Some auto-tests had to be update to to take the new behavior
into account.

[ChangeLog][QtWidgets][Styles] Added SH_ItemView_ScrollMode
style hint.

[ChangeLog][QtWidgets][Item Views] Item views scroll per pixel
on OS X now.

[ChangeLog][QtWidgets][Item Views] QAbstractItemView::verticalScrollMode
and QAbstractItemView::horizontalScrollMode are now resettable.

Change-Id: I3f923275c99aa4389323b52fc1c5455fe71f8d73
Task-number: QTBUG-50102
Reviewed-by: Jake Petroules <jake.petroules@theqtcompany.com>

3 files changed, 72 insertions, 8 deletions

diff --git a/tests/auto/widgets/itemviews/qabstractitemview/tst_qabstractitemview.cpp b/tests/auto/widgets/itemviews/qabstractitemview/tst_qabstractitemview.cpp
index 2a26427542..2dd0337117 100644
--- a/tests/auto/widgets/itemviews/qabstractitemview/tst_qabstractitemview.cpp
+++ b/tests/auto/widgets/itemviews/qabstractitemview/tst_qabstractitemview.cpp
@@ -50,6 +50,7 @@
 #include <qstyleditemdelegate.h>
 #include <qstringlistmodel.h>
 #include <qsortfilterproxymodel.h>
+#include <qproxystyle.h>
 
 static inline void setFrameless(QWidget *w)
 {
@@ -246,6 +247,7 @@ private slots:
     void sizeHintChangeTriggersLayout();
     void shiftSelectionAfterChangingModelContents();
     void QTBUG48968_reentrant_updateEditorGeometries();
+    void QTBUG50102_SH_ItemView_ScrollMode();
 };
 
 class MyAbstractItemDelegate : public QAbstractItemDelegate
@@ -2018,5 +2020,53 @@ void tst_QAbstractItemView::QTBUG48968_reentrant_updateEditorGeometries()
     // No crash, all fine.
 }
 
+class ScrollModeProxyStyle: public QProxyStyle
+{
+public:
+    ScrollModeProxyStyle(QAbstractItemView::ScrollMode sm, QStyle *style = 0)
+        : QProxyStyle(style)
+        , scrollMode(sm == QAbstractItemView::ScrollPerItem ?
+                     QAbstractItemView::ScrollPerPixel : QAbstractItemView::ScrollPerItem)
+    { }
+
+    int styleHint(QStyle::StyleHint hint, const QStyleOption *opt, const QWidget *w, QStyleHintReturn *returnData) const override
+    {
+        if (hint == SH_ItemView_ScrollMode)
+            return scrollMode;
+
+        return baseStyle()->styleHint(hint, opt, w, returnData);
+    }
+
+    QAbstractItemView::ScrollMode scrollMode;
+};
+
+void tst_QAbstractItemView::QTBUG50102_SH_ItemView_ScrollMode()
+{
+    QListView view;
+
+    // Default comes from the style
+    auto styleScrollMode = static_cast<QAbstractItemView::ScrollMode>(view.style()->styleHint(QStyle::SH_ItemView_ScrollMode, 0, &view, 0));
+    QCOMPARE(view.verticalScrollMode(), styleScrollMode);
+    QCOMPARE(view.horizontalScrollMode(), styleScrollMode);
+
+    // Change style, get new value
+    view.setStyle(new ScrollModeProxyStyle(styleScrollMode));
+    auto proxyScrollMode = static_cast<QAbstractItemView::ScrollMode>(view.style()->styleHint(QStyle::SH_ItemView_ScrollMode, 0, &view, 0));
+    QVERIFY(styleScrollMode != proxyScrollMode);
+    QCOMPARE(view.verticalScrollMode(), proxyScrollMode);
+    QCOMPARE(view.horizontalScrollMode(), proxyScrollMode);
+
+    // Explicitly set vertical, same value
+    view.setVerticalScrollMode(proxyScrollMode);
+    QCOMPARE(view.verticalScrollMode(), proxyScrollMode);
+    QCOMPARE(view.horizontalScrollMode(), proxyScrollMode);
+
+    // Change style, won't change value for vertical, will change for horizontal
+    view.setStyle(new ScrollModeProxyStyle(proxyScrollMode));
+    QCOMPARE(view.verticalScrollMode(), proxyScrollMode);
+    QCOMPARE(view.horizontalScrollMode(), styleScrollMode);
+}
+
+
 QTEST_MAIN(tst_QAbstractItemView)
 #include "tst_qabstractitemview.moc"
diff --git a/tests/auto/widgets/itemviews/qlistview/tst_qlistview.cpp b/tests/auto/widgets/itemviews/qlistview/tst_qlistview.cpp
index ea9f20d5ba..5058dd2a81 100644
--- a/tests/auto/widgets/itemviews/qlistview/tst_qlistview.cpp
+++ b/tests/auto/widgets/itemviews/qlistview/tst_qlistview.cpp
@@ -279,6 +279,18 @@ public:
     mutable bool wrongIndex;
 };
 
+class ScrollPerItemListView : public QListView
+{
+public:
+    explicit ScrollPerItemListView(QWidget *parent = Q_NULLPTR)
+        : QListView(parent)
+    {
+        // Force per item scroll mode since it comes from the style by default
+        setVerticalScrollMode(QAbstractItemView::ScrollPerItem);
+        setHorizontalScrollMode(QAbstractItemView::ScrollPerItem);
+    }
+};
+
 void tst_QListView::initTestCase()
 {
 #ifdef Q_OS_WINCE //disable magic for WindowsCE
@@ -823,7 +835,7 @@ void tst_QListView::setCurrentIndex()
 {
     QStringListModel model(generateList(QLatin1String("item "), 20));
 
-    QListView view;
+    ScrollPerItemListView view;
     view.setModel(&model);
 
     view.resize(220,182);
@@ -1153,7 +1165,7 @@ void tst_QListView::scrollTo()
 {
     QWidget topLevel;
     setFrameless(&topLevel);
-    QListView lv(&topLevel);
+    ScrollPerItemListView lv(&topLevel);
     QStringListModel model(&lv);
     QStringList list;
     list << "Short item 1";
@@ -1189,6 +1201,7 @@ void tst_QListView::scrollTo()
     model.setStringList(list);
     lv.setModel(&model);
     lv.setFixedSize(110, 200);
+
     topLevel.show();
     QVERIFY(QTest::qWaitForWindowExposed(&topLevel));
 
@@ -1262,7 +1275,7 @@ void tst_QListView::scrollBarRanges()
     const int rowHeight = 20;
 
     QWidget topLevel;
-    QListView lv(&topLevel);
+    ScrollPerItemListView lv(&topLevel);
     QStringListModel model(&lv);
     QStringList list;
     for (int i = 0; i < rowCount; ++i)
@@ -1271,6 +1284,7 @@ void tst_QListView::scrollBarRanges()
     model.setStringList(list);
     lv.setModel(&model);
     lv.resize(250, 130);
+
     TestDelegate *delegate = new TestDelegate(&lv);
     delegate->m_sizeHint = QSize(100, rowHeight);
     lv.setItemDelegate(delegate);
@@ -1814,7 +1828,7 @@ void tst_QListView::taskQTBUG_2233_scrollHiddenItems()
 
     QWidget topLevel;
     setFrameless(&topLevel);
-    QListView view(&topLevel);
+    ScrollPerItemListView view(&topLevel);
     QStringListModel model(&view);
     QStringList list;
     for (int i = 0; i < rowCount; ++i)
@@ -2060,7 +2074,7 @@ void tst_QListView::taskQTBUG_21115_scrollToAndHiddenItems()
 {
     QFETCH(int, flow);
 
-    QListView lv;
+    ScrollPerItemListView lv;
     lv.setUniformItemSizes(true);
     lv.setFlow(static_cast<QListView::Flow>(flow));
 
@@ -2155,7 +2169,7 @@ void tst_QListView::taskQTBUG_21804_hiddenItemsAndScrollingWithKeys()
     model.setStringList(list);
 
     // create listview
-    QListView lv;
+    ScrollPerItemListView lv;
     lv.setFlow(static_cast<QListView::Flow>(flow));
     lv.setSpacing(spacing);
     lv.setModel(&model);
@@ -2227,7 +2241,7 @@ void tst_QListView::spacing()
     model.setStringList(list);
 
     // create listview
-    QListView lv;
+    ScrollPerItemListView lv;
     lv.setFlow(static_cast<QListView::Flow>(flow));
     lv.setModel(&model);
     lv.setSpacing(spacing);
diff --git a/tests/auto/widgets/itemviews/qtreeview/tst_qtreeview.cpp b/tests/auto/widgets/itemviews/qtreeview/tst_qtreeview.cpp
index e21aedee1e..137f18e23a 100644
--- a/tests/auto/widgets/itemviews/qtreeview/tst_qtreeview.cpp
+++ b/tests/auto/widgets/itemviews/qtreeview/tst_qtreeview.cpp
@@ -503,7 +503,7 @@ void tst_QTreeView::construction()
     QCOMPARE(view.sizeHintForRow(1), -1);
     QVERIFY(!view.tabKeyNavigation());
     QCOMPARE(view.textElideMode(), Qt::ElideRight);
-    QCOMPARE(view.verticalScrollMode(), QAbstractItemView::ScrollPerItem);
+    QCOMPARE(static_cast<int>(view.verticalScrollMode()), view.style()->styleHint(QStyle::SH_ItemView_ScrollMode, 0, &view));
     QCOMPARE(view.visualRect(QModelIndex()), QRect());
 
     // QTreeView properties