From 1c1cce67fa1d03a49cdfb6f1ca378b182925ffdb Mon Sep 17 00:00:00 2001
From: Pavel Krebs <pkrebs@amberg.cz>
Date: Fri, 5 Dec 2014 15:39:48 +0100
Subject: [PATCH] QScrollBar: emit valueChanged once even if a slot takes too
 much time

Put also processing of control activation into initial timer check for possibly
pending mouse release event.

[ChangeLog][QtWidgets][QScrollBar] Fixed a bug where the valueChanged() signal
was emitted twice if a connected slot took too much time.

Task-number: QTBUG-42871
Change-Id: I7bad5279ef84463a033b55256d241d4445374081
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
---
 src/widgets/widgets/qscrollbar.cpp            |  7 ++--
 .../widgets/qscrollbar/tst_qscrollbar.cpp     | 40 +++++++++++++++++++
 2 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/src/widgets/widgets/qscrollbar.cpp b/src/widgets/widgets/qscrollbar.cpp
index 58510203799..c2d2117e209 100644
--- a/src/widgets/widgets/qscrollbar.cpp
+++ b/src/widgets/widgets/qscrollbar.cpp
@@ -593,13 +593,14 @@ void QScrollBar::mousePressEvent(QMouseEvent *e)
         d->clickOffset = sliderLength / 2;
     }
     const int initialDelay = 500; // default threshold
-    d->activateControl(d->pressedControl, initialDelay);
     QElapsedTimer time;
     time.start();
+    d->activateControl(d->pressedControl, initialDelay);
     repaint(style()->subControlRect(QStyle::CC_ScrollBar, &opt, d->pressedControl, this));
     if (time.elapsed() >= initialDelay && d->repeatActionTimer.isActive()) {
-        // It took more than 500ms (the initial timer delay) to process the repaint(), we
-        // therefore need to restart the timer in case we have a pending mouse release event;
+        // It took more than 500ms (the initial timer delay) to process
+        // the control activation and repaint(), we therefore need
+        // to restart the timer in case we have a pending mouse release event;
         // otherwise we'll get a timer event right before the release event,
         // causing the repeat action to be invoked twice on a single mouse click.
         // 50ms is the default repeat time (see activateControl/setRepeatAction).
diff --git a/tests/auto/widgets/widgets/qscrollbar/tst_qscrollbar.cpp b/tests/auto/widgets/widgets/qscrollbar/tst_qscrollbar.cpp
index cb0383c3987..008d3b24355 100644
--- a/tests/auto/widgets/widgets/qscrollbar/tst_qscrollbar.cpp
+++ b/tests/auto/widgets/widgets/qscrollbar/tst_qscrollbar.cpp
@@ -58,6 +58,7 @@ private slots:
 #ifndef QT_NO_WHEELEVENT
     void QTBUG_27308();
 #endif
+    void QTBUG_42871();
 };
 
 class SingleStepTestScrollBar : public QScrollBar {
@@ -169,5 +170,44 @@ void tst_QScrollBar::QTBUG_27308()
 }
 #endif
 
+class QTBUG_42871_Handler : public QObject {
+    Q_OBJECT
+public:
+    int updatesCount;
+    QTBUG_42871_Handler() : QObject(), updatesCount(0) {}
+public slots:
+    void valueUpdated(int) { ++updatesCount; QTest::qSleep(600); }
+};
+
+void tst_QScrollBar::QTBUG_42871()
+{
+    QTBUG_42871_Handler myHandler;
+    QScrollBar scrollBarWidget(Qt::Vertical);
+    bool connection = connect(&scrollBarWidget, SIGNAL(valueChanged(int)), &myHandler, SLOT(valueUpdated(int)));
+    QVERIFY(connection);
+    scrollBarWidget.resize(100, scrollBarWidget.height());
+    centerOnScreen(&scrollBarWidget);
+    scrollBarWidget.show();
+    QTest::qWaitForWindowExposed(&scrollBarWidget);
+    QSignalSpy spy(&scrollBarWidget, SIGNAL(actionTriggered(int)));
+    QVERIFY(spy.isValid());
+    QCOMPARE(myHandler.updatesCount, 0);
+    QCOMPARE(spy.count(), 0);
+
+    // Simulate a mouse click on the "scroll down button".
+    const QPoint pressPoint(scrollBarWidget.width() / 2, scrollBarWidget.height() - 10);
+    const QPoint globalPressPoint = scrollBarWidget.mapToGlobal(pressPoint);
+    QMouseEvent mousePressEvent(QEvent::MouseButtonPress, pressPoint, globalPressPoint,
+                                Qt::LeftButton, Qt::LeftButton, 0);
+    QApplication::sendEvent(&scrollBarWidget, &mousePressEvent);
+    QTest::qWait(1);
+    QMouseEvent mouseReleaseEvent(QEvent::MouseButtonRelease, pressPoint, globalPressPoint,
+                                  Qt::LeftButton, Qt::LeftButton, 0);
+    QApplication::sendEvent(&scrollBarWidget, &mouseReleaseEvent);
+    // Check that the action was triggered once.
+    QCOMPARE(myHandler.updatesCount, 1);
+    QCOMPARE(spy.count(), 1);
+}
+
 QTEST_MAIN(tst_QScrollBar)
 #include "tst_qscrollbar.moc"