qml: Fix warnings about dereferencing null types

src/private/quick/FrameQuick.cpp

@@ -53,6 +53,7 @@ DockWidgetModel *FrameQuick::dockWidgetModel() const
 void FrameQuick::removeWidget_impl(DockWidgetBase *dw)
 {
     m_dockWidgetModel->remove(dw);
+    disconnect(m_connections.take(dw));
 }
 
 void FrameQuick::detachTab_impl(DockWidgetBase *)
@@ -93,6 +94,13 @@ void FrameQuick::insertDockWidget_impl(DockWidgetBase *dw, int index)
     if (m_dockWidgetModel->insert(dw, index)) {
         dw->setParent(m_stackLayout);
 
+        QMetaObject::Connection conn = connect(dw, &DockWidgetBase::parentChanged, this, [dw, this] {
+            if (dw->parent() != m_stackLayout)
+                removeWidget_impl(dw);
+        });
+
+        m_connections[dw] = conn;
+
         if (!m_currentDockWidget)
             m_currentDockWidget = dw;
     }
@@ -191,8 +199,9 @@ void DockWidgetModel::remove(DockWidgetBase *dw)
     if (row == -1) {
         qWarning() << Q_FUNC_INFO << "Nothing to remove" << dw;
     } else {
-        disconnect(m_connections.value(dw));
-        m_connections.remove(dw);
+        const auto connections = m_connections.take(dw);
+        for (QMetaObject::Connection conn : connections)
+            disconnect(conn);
 
         beginRemoveRows(QModelIndex(), row, row);
         m_dockWidgets.removeOne(dw);
@@ -214,11 +223,11 @@ bool DockWidgetModel::insert(DockWidgetBase *dw, int index)
         return false;
     }
 
-    QMetaObject::Connection c = connect(dw, &DockWidgetBase::titleChanged, this, [dw, this] {
+    QMetaObject::Connection conn = connect(dw, &DockWidgetBase::titleChanged, this, [dw, this] {
         emitDataChangedFor(dw);
     });
 
-    m_connections.insert(dw, c);
+    m_connections[dw] = { conn };
 
     beginInsertRows(QModelIndex(), index, index);
     m_dockWidgets.insert(index, dw);

src/private/quick/FrameQuick_p.h

@@ -53,6 +53,7 @@ private:
     QQuickItem *m_stackLayout = nullptr;
     DockWidgetBase *m_currentDockWidget = nullptr;
     DockWidgetModel *const m_dockWidgetModel;
+    QHash<DockWidgetBase *, QMetaObject::Connection> m_connections; // To make it easy to disconnect from lambdas
 };
 
 class DockWidgetModel : public QAbstractListModel
@@ -79,7 +80,7 @@ Q_SIGNALS:
 private:
     void emitDataChangedFor(DockWidgetBase *);
     DockWidgetBase::List m_dockWidgets;
-    QHash<DockWidgetBase *, QMetaObject::Connection> m_connections; // To make it easy to disconnect from lambda
+    QHash<DockWidgetBase *, QVector<QMetaObject::Connection> > m_connections; // To make it easy to disconnect from lambdas
 };
 
 }

src/private/quick/QWidgetAdapter_quick.cpp

@@ -71,6 +71,7 @@ void QWidgetAdapter::itemChange(QQuickItem::ItemChange change, const QQuickItem:
     case QQuickItem::ItemVisibleHasChanged: {
         QEvent ev(QEvent::ParentChange);
         event(&ev);
+        Q_EMIT parentChanged();
         break;
     }
     case QQuickItem::ItemParentHasChanged: {

src/private/quick/QWidgetAdapter_quick_p.h

@@ -106,6 +106,8 @@ public:
     Qt::WindowFlags windowFlags() const;
 
     QQuickItem *createItem(QQmlEngine *, const QString &filename) const;
+Q_SIGNALS:
+    void parentChanged();
 protected:
     void raiseAndActivate();
     virtual bool onResize(QSize newSize);

src/private/quick/qml/FloatingWindow.qml

@@ -47,7 +47,9 @@ Rectangle {
 
     onDropAreaCppChanged: {
         // Parent the cpp obj to the visual obj. So the user can style it
-        dropAreaCpp.parent = dropArea;
-        dropAreaCpp.anchors.fill = dropArea;
+        if (dropAreaCpp) {
+            dropAreaCpp.parent = dropArea;
+            dropAreaCpp.anchors.fill = dropArea;
+        }
     }
 }

src/private/quick/qml/Frame.qml

@@ -22,7 +22,8 @@ Rectangle {
     anchors.fill: parent
 
     onFrameCppChanged: {
-        frameCpp.setStackLayout(stackLayout);
+        if (frameCpp)
+            frameCpp.setStackLayout(stackLayout);
     }
 
     TitleBar {

src/private/quick/qml/TitleBarBase.qml

@@ -26,6 +26,7 @@ Rectangle {
     }
 
     onTitleBarCppChanged: {
-        titleBarCpp.filterEvents(dragMouseArea)
+        if (titleBarCpp)
+            titleBarCpp.filterEvents(dragMouseArea)
     }
 }