Add the QTabBar::changeCurrentOnDrag property.

This property indicates that the current tab will change whilst dragging
over the tabbar

[ChangeLog][QtWidgets][QTabBar] Added changeCurrentOnDrag property.

Change-Id: Ib7d5a7613c9cd8432b84c523f66c02cd6c3c3c81
Reviewed-by: David Faure <david.faure@kdab.com>

src/widgets/styles/qcommonstyle.cpp

@@ -5109,6 +5109,9 @@ int QCommonStyle::styleHint(StyleHint sh, const QStyleOption *opt, const QWidget
     case SH_TabBar_CloseButtonPosition:
         ret = QTabBar::RightSide;
         break;
+    case SH_TabBar_ChangeCurrentDelay:
+        ret = 500;
+        break;
 #endif
     case SH_DockWidget_ButtonsHaveFrame:
         ret = true;

src/widgets/styles/qstyle.cpp

@@ -1930,6 +1930,10 @@ void QStyle::drawItemPixmap(QPainter *painter, const QRect &rect, int alignment,
     \value SH_Splitter_OpaqueResize Determines if resizing is opaque
            This enum value has been introduced in Qt 5.2
 
+    \value SH_TabBar_ChangeCurrentDelay Determines the delay before the current
+           tab is changed while dragging over the tabbar, in milliseconds. This
+           enum value has been introduced in Qt 5.4
+
     \sa styleHint()
 */
 

src/widgets/styles/qstyle.h

@@ -704,6 +704,7 @@ public:
         SH_Splitter_OpaqueResize,
         SH_ComboBox_UseNativePopup,
         SH_LineEdit_PasswordMaskDelay,
+        SH_TabBar_ChangeCurrentDelay,
         // Add new style hint values here
 
         SH_CustomBase = 0xf0000000

src/widgets/widgets/qtabbar.cpp

@@ -588,6 +588,16 @@ void QTabBarPrivate::makeVisible(int index)
     }
 }
 
+void QTabBarPrivate::killSwitchTabTimer()
+{
+    Q_Q(QTabBar);
+    if (switchTabTimerId) {
+        q->killTimer(switchTabTimerId);
+        switchTabTimerId = 0;
+    }
+    switchTabCurrentIndex = -1;
+}
+
 void QTabBarPrivate::layoutTab(int index)
 {
     Q_Q(QTabBar);
@@ -1527,6 +1537,26 @@ bool QTabBar::event(QEvent *event)
     } else if (event->type() == QEvent::Move) {
         d->updateMacBorderMetrics();
         return QWidget::event(event);
+
+#ifndef QT_NO_DRAGANDDROP
+    } else if (event->type() == QEvent::DragEnter) {
+        if (d->changeCurrentOnDrag)
+            event->accept();
+    } else if (event->type() == QEvent::DragMove) {
+        if (d->changeCurrentOnDrag) {
+            const int tabIndex = tabAt(static_cast<QDragMoveEvent *>(event)->pos());
+            if (isTabEnabled(tabIndex) && d->switchTabCurrentIndex != tabIndex) {
+                d->switchTabCurrentIndex = tabIndex;
+                if (d->switchTabTimerId)
+                    killTimer(d->switchTabTimerId);
+                d->switchTabTimerId = startTimer(style()->styleHint(QStyle::SH_TabBar_ChangeCurrentDelay));
+            }
+            event->ignore();
+        }
+    } else if (event->type() == QEvent::DragLeave || event->type() == QEvent::Drop) {
+        d->killSwitchTabTimer();
+        event->ignore();
+#endif
     }
     return QWidget::event(event);
 }
@@ -2044,6 +2074,21 @@ void QTabBar::changeEvent(QEvent *event)
     QWidget::changeEvent(event);
 }
 
+/*!
+    \reimp
+*/
+void QTabBar::timerEvent(QTimerEvent *event)
+{
+    Q_D(QTabBar);
+    if (event->timerId() == d->switchTabTimerId) {
+        killTimer(d->switchTabTimerId);
+        d->switchTabTimerId = 0;
+        setCurrentIndex(d->switchTabCurrentIndex);
+        d->switchTabCurrentIndex = -1;
+    }
+    QWidget::timerEvent(event);
+}
+
 /*!
     \property QTabBar::elideMode
     \brief how to elide text in the tab bar
@@ -2306,6 +2351,32 @@ void QTabBar::setAutoHide(bool hide)
         setVisible(true);
 }
 
+/*!
+    \property QTabBar::changeCurrentOnDrag
+    \brief If true, then the current tab is automatically changed when dragging
+    over the tabbar.
+    \since 5.4
+
+    \note You should also set acceptDrops property to true to make this feature
+    work.
+
+    By default, this property is false.
+*/
+
+bool QTabBar::changeCurrentOnDrag() const
+{
+    Q_D(const QTabBar);
+    return d->changeCurrentOnDrag;
+}
+
+void QTabBar::setChangeCurrentOnDrag(bool change)
+{
+    Q_D(QTabBar);
+    d->changeCurrentOnDrag = change;
+    if (!change)
+        d->killSwitchTabTimer();
+}
+
 /*!
     Sets \a widget on the tab \a index.  The widget is placed
     on the left or right hand side depending upon the \a position.

src/widgets/widgets/qtabbar.h

@@ -71,6 +71,7 @@ class Q_WIDGETS_EXPORT QTabBar: public QWidget
     Q_PROPERTY(bool movable READ isMovable WRITE setMovable)
     Q_PROPERTY(bool documentMode READ documentMode WRITE setDocumentMode)
     Q_PROPERTY(bool autoHide READ autoHide WRITE setAutoHide)
+    Q_PROPERTY(bool changeCurrentOnDrag READ changeCurrentOnDrag WRITE setChangeCurrentOnDrag)
 
 public:
     explicit QTabBar(QWidget* parent=0);
@@ -170,6 +171,9 @@ public:
     bool autoHide() const;
     void setAutoHide(bool hide);
 
+    bool changeCurrentOnDrag() const;
+    void setChangeCurrentOnDrag(bool change);
+
 public Q_SLOTS:
     void setCurrentIndex(int index);
 
@@ -200,6 +204,7 @@ protected:
 #endif
     void keyPressEvent(QKeyEvent *);
     void changeEvent(QEvent *);
+    void timerEvent(QTimerEvent *event);
     void initStyleOption(QStyleOptionTab *option, int tabIndex) const;
 
 #ifndef QT_NO_ACCESSIBILITY

src/widgets/widgets/qtabbar_p.h

@@ -77,7 +77,8 @@ public:
         :currentIndex(-1), pressedIndex(-1), shape(QTabBar::RoundedNorth), layoutDirty(false),
         drawBase(true), scrollOffset(0), elideModeSetByUser(false), useScrollButtonsSetByUser(false), expanding(true), closeButtonOnTabs(false),
         selectionBehaviorOnRemove(QTabBar::SelectRightTab), paintWithOffsets(true), movable(false),
-        dragInProgress(false), documentMode(false), autoHide(false), movingTab(0)
+        dragInProgress(false), documentMode(false), autoHide(false), changeCurrentOnDrag(false),
+        switchTabCurrentIndex(-1), switchTabTimerId(0), movingTab(0)
 #ifdef Q_WS_MAC
         , previousPressedIndex(-1)
 #endif
@@ -203,6 +204,10 @@ public:
     bool dragInProgress;
     bool documentMode;
     bool autoHide;
+    bool changeCurrentOnDrag;
+
+    int switchTabCurrentIndex;
+    int switchTabTimerId;
 
     QWidget *movingTab;
 #ifdef Q_WS_MAC
@@ -242,6 +247,8 @@ public:
         }
     }
 
+    void killSwitchTabTimer();
+
 };
 
 class CloseButton : public QAbstractButton