Add Controller::setParentView()

Controllers need to know when the view changes parent. Until know
they listen to event filter's QEvent::ParentChange, which isn't portable
to non-Qt platforms. Instead, always go through the controller.
Then each controller can override setParentView(), which is virtual,
to intercept parent changes without any Qt specific events.

In a followup will inherit from setParentView() in a few controllers

src/Controller.cpp

@@ -124,3 +124,12 @@ void Controller::show() const
 {
     return view()->show();
 }
+
+void Controller::setParentView(View *parent)
+{
+    if (auto v = view()) {
+        v->setParent(parent);
+    } else {
+        qWarning() << Q_FUNC_INFO << "No view()";
+    }
+}

src/Controller.h

@@ -80,6 +80,10 @@ public:
     void show() const;
     bool inDtor() const;
 
+    /// Sets the parent view
+    /// In Qt this would be equivalent to calling view()->setParent(parent);
+    virtual void setParentView(View *parent);
+
 private:
     void setParent(QObject *) = delete;
     View *m_view = nullptr;

src/private/multisplitter/Item.cpp

@@ -185,7 +185,7 @@ void Item::setGuestView(View *guest)
     m_layoutInvalidatedConnection->disconnect();
 
     if (m_guest) {
-        m_guest->setParent(m_hostWidget);
+        m_guest->controller()->setParentView(m_hostWidget);
         if (Controllers::Group *group = asGroupController())
             group->setLayoutItem(this);