Port frameParent() to firstParentOfType()

src/private/DockRegistry.cpp

@@ -711,7 +711,7 @@ bool DockRegistry::eventFilter(QObject *watched, QEvent *event)
         }
     } else if (event->type() == QEvent::MouseButtonPress) {
         // When clicking on a MDI Frame we raise the window
-        if (Frame *f = parentFrame(watched)) {
+        if (Frame *f = firstParentOfType<Frame>(watched)) {
             if (f->isMDI())
                 f->raise();
         }

src/private/TitleBar.cpp

@@ -18,6 +18,7 @@
 #include "FrameworkWidgetFactory.h"
 #include "Config.h"
 #include "MainWindowBase.h"
+#include "MDILayoutWidget_p.h"
 
 #include <QTimer>
 #include <QWindowStateChangeEvent>
@@ -100,10 +101,7 @@ MainWindowBase *TitleBar::mainWindow() const
 
 bool TitleBar::isMDI() const
 {
-    if (auto mw = mainWindow())
-        return mw->isMDI();
-
-    return false;
+    return firstParentOfType<MDILayoutWidget>(this) != nullptr;
 }
 
 void TitleBar::updateButtons()

src/private/TitleBar_p.h

@@ -112,9 +112,8 @@ public:
     ///Returns nullptr otherwise
     MainWindowBase *mainWindow() const;
 
-    /// @brief Returns if this title bar is in a main window in MDI mode
-    /// By default false. Only relevant if your main window was constructed with the
-    /// MainWindowOption_MDI option
+    /// @brief Returns if this title bar belongs to a dock widget which is in MDI mode (inside a MDI area)
+    /// For example in a main window created with MainWindowOption_MDI option
     bool isMDI() const override;
 
     /// @brief updates the close button enabled state

src/private/Utils_p.h

@@ -362,13 +362,18 @@ inline bool scalingFactorIsSupported(qreal factor)
 #endif
 }
 
-/// @brief Returns the parent frame which the specified object is in, if any
-inline Frame *parentFrame(QObject *from)
+template <typename T>
+inline T* firstParentOfType(const QObject *child)
 {
-    auto p = from;
+    auto p = const_cast<QObject *>(child);
     while (p) {
-        if (auto frame = qobject_cast<Frame *>(p))
-            return frame;
+        if (qobject_cast<const QWindow*>(p)) {
+            // Ignore QObject hierarchies spanning though multiple windows
+            return nullptr;
+        }
+
+        if (auto candidate = qobject_cast<T *>(p))
+            return candidate;
 
         p = p->parent();
     }

tests/tst_docks.cpp

@@ -7526,4 +7526,14 @@ void TestDocks::tst_mdi_mixed_with_docking()
 
     mdiArea->addDockWidget(mdiWidget1, QPoint(10, 10));
     mdiArea->addDockWidget(mdiWidget2, QPoint(50, 50));
-}
+
+    Frame *frameMDI1 = mdiWidget1->d->frame();
+    Frame *frame1 = dock1->d->frame();
+    QVERIFY(!frame1->isMDI());
+    QVERIFY(frameMDI1->isMDI());
+    QVERIFY(!frame1->mdiLayoutWidget());
+    QVERIFY(frameMDI1->mdiLayoutWidget());
+
+    QVERIFY(!dock1->titleBar()->isMDI());
+    QVERIFY(mdiWidget1->titleBar()->isMDI());
+}