QComboBox - only react on a mouse-release if we had a mousepress

In delegates we get into trouble with calling showPopup in
setEditorData (edit by double click) - and that is not reasonable.
The user has requested edit - and therefore it is natural to save
a click for the user and show the popup at once.

However that fails since we have the mouse down and as soon as we
release the mouse we will call hidePopup.

This patch ensures that the mouseReleaseEvent, that caused the
problem is only considered if we have had a mousePressEvent.

Change-Id: Ibe031fcb9ad2158f6969e41127bbb5f651b9cae6
Reviewed-by: Stephen Kelly <stephen.kelly@kdab.com>

src/widgets/widgets/qcombobox.cpp

@@ -407,7 +407,7 @@ void QComboBoxPrivateContainer::leaveEvent(QEvent *)
 }
 
 QComboBoxPrivateContainer::QComboBoxPrivateContainer(QAbstractItemView *itemView, QComboBox *parent)
-    : QFrame(parent, Qt::Popup), combo(parent), view(0), top(0), bottom(0)
+    : QFrame(parent, Qt::Popup), combo(parent), view(0), top(0), bottom(0), maybeIgnoreMouseButtonRelease(false)
 {
     // we need the combobox and itemview
     Q_ASSERT(parent);
@@ -667,10 +667,15 @@ bool QComboBoxPrivateContainer::eventFilter(QObject *o, QEvent *e)
             }
         }
         break;
+    case QEvent::MouseButtonPress:
+        maybeIgnoreMouseButtonRelease = false;
+        break;
     case QEvent::MouseButtonRelease: {
+        bool ignoreEvent = maybeIgnoreMouseButtonRelease && popupTimer.elapsed() < QApplication::doubleClickInterval();
+
         QMouseEvent *m = static_cast<QMouseEvent *>(e);
         if (isVisible() && view->rect().contains(m->pos()) && view->currentIndex().isValid()
-            && !blockMouseReleaseTimer.isActive()
+            && !blockMouseReleaseTimer.isActive() && !ignoreEvent
             && (view->currentIndex().flags() & Qt::ItemIsEnabled)
             && (view->currentIndex().flags() & Qt::ItemIsSelectable)) {
             combo->hidePopup();
@@ -2562,6 +2567,7 @@ void QComboBox::showPopup()
     container->setUpdatesEnabled(false);
 #endif
 
+    bool startTimer = !container->isVisible();
     container->raise();
     container->show();
     container->updateScrollers();
@@ -2581,6 +2587,10 @@ void QComboBox::showPopup()
     if (QApplication::keypadNavigationEnabled())
         view()->setEditFocus(true);
 #endif
+    if (startTimer) {
+        container->popupTimer.start();
+        container->maybeIgnoreMouseButtonRelease = true;
+    }
 }
 
 /*!
@@ -2876,6 +2886,11 @@ void QComboBox::mousePressEvent(QMouseEvent *e)
         }
 #endif
         showPopup();
+        // The code below ensures that regular mousepress and pick item still works
+        // If it was not called the viewContainer would ignore event since it didn't have
+        // a mousePressEvent first.
+        if (d->viewContainer())
+            d->viewContainer()->maybeIgnoreMouseButtonRelease = false;
     } else {
 #ifdef QT_KEYPAD_NAVIGATION
         if (QApplication::keypadNavigationEnabled() && sc == QStyle::SC_ComboBoxEditField && d->lineEdit) {

src/widgets/widgets/qcombobox_p.h

@@ -254,6 +254,10 @@ private:
     QAbstractItemView *view;
     QComboBoxPrivateScroller *top;
     QComboBoxPrivateScroller *bottom;
+    bool maybeIgnoreMouseButtonRelease;
+    QElapsedTimer popupTimer;
+
+    friend class QComboBox;
 };
 
 class QComboMenuDelegate : public QAbstractItemDelegate

tests/manual/widgets/itemviews/delegate/example.cpp

@@ -45,6 +45,7 @@
 #include <QStandardItemModel>
 #include <QItemDelegate>
 #include <QDebug>
+#include <QComboBox>
 
 class ExampleEditor : public QLineEdit
 {
@@ -56,13 +57,26 @@ public:
 class ExampleDelegate : public QItemDelegate
 {
 public:
-    ExampleDelegate():QItemDelegate() { m_editor = new ExampleEditor(0); }
-protected:
-    QWidget* createEditor(QWidget *p, const QStyleOptionViewItem &o, const QModelIndex &) const
+    ExampleDelegate() : QItemDelegate()
     {
-        m_editor->setParent(p);
-        m_editor->setGeometry(o.rect);
-        return m_editor;
+        m_editor = new ExampleEditor(0);
+        m_combobox = new QComboBox(0);
+        m_combobox->addItem(QString::fromUtf8("item1"));
+        m_combobox->addItem(QString::fromUtf8("item2"));
+    }
+protected:
+    QWidget* createEditor(QWidget *p, const QStyleOptionViewItem &o, const QModelIndex &i) const
+    {
+        // doubleclick rownumber 3 (last row) to see the difference.
+        if (i.row() == 3) {
+            m_combobox->setParent(p);
+            m_combobox->setGeometry(o.rect);
+            return m_combobox;
+        } else {
+            m_editor->setParent(p);
+            m_editor->setGeometry(o.rect);
+            return m_editor;
+        }
     }
     void destroyEditor(QWidget *editor, const QModelIndex &) const
     {
@@ -71,10 +85,25 @@ protected:
     }
 
     // Avoid setting data - and therefore show that the editor keeps its state.
-    void setEditorData(QWidget*, const QModelIndex &) const { }
+    void setEditorData(QWidget* w, const QModelIndex &) const
+    {
+        QComboBox *combobox = qobject_cast<QComboBox*>(w);
+        if (combobox) {
+            qDebug() << "Try to show popup at once";
+            // Now we could try to make a call to
+            // QCoreApplication::processEvents();
+            // But it does not matter. The fix:
+            // https://codereview.qt-project.org/40608
+            // is blocking QComboBox from reacting to this doubleclick edit event
+            // and we need to do that since the mouseReleaseEvent has not yet happened,
+            // and therefore cannot be processed.
+            combobox->showPopup();
+        }
+    }
 
     ~ExampleDelegate() { delete m_editor; }
     mutable ExampleEditor *m_editor;
+    mutable QComboBox *m_combobox;
 };
 
 int main(int argc, char *argv[])