Introduce main window affinity

By default a dock widget can dock into any main window.
With affinities, we can now have a dock widget "belong" to a main window
and only be able to dock into it (or into other floating dock widgets
with the same affinity).

See DockWidgetBase::setAffinity() and MainWindowBase::setAffinity().

examples/dockwidgets/MyMainWindow.cpp

@@ -49,8 +49,9 @@ static MyWidget *newMyWidget()
     }
 }
 
-MyMainWindow::MyMainWindow(KDDockWidgets::MainWindowOptions options, QWidget *parent)
-    : MainWindow(QStringLiteral("MyMainWindow"), options, parent)
+MyMainWindow::MyMainWindow(const QString &uniqueName, KDDockWidgets::MainWindowOptions options,
+                           const QString &affinityName, QWidget *parent)
+    : MainWindow(uniqueName, options, parent)
 {
     // qApp->installEventFilter(this);
 
@@ -88,6 +89,7 @@ MyMainWindow::MyMainWindow(KDDockWidgets::MainWindowOptions options, QWidget *pa
         saver.restoreFromDisk();
     });
 
+    setAffinityName(affinityName);
     createDockWidgets();
 }
 
@@ -124,6 +126,7 @@ KDDockWidgets::DockWidgetBase *MyMainWindow::newDockWidget()
 {
     static int count = 0;
     auto dock = new KDDockWidgets::DockWidget(QStringLiteral("DockWidget #%1").arg(count));
+    dock->setAffinityName(affinityName()); // optional, just to show the feature. Pass -mi to the example to see incompatible dock widgets
 
     if (count == 1)
         dock->setIcon(QIcon::fromTheme(QStringLiteral("mail-message")));

examples/dockwidgets/MyMainWindow.h

@@ -26,7 +26,9 @@ class MyMainWindow : public KDDockWidgets::MainWindow
 {
     Q_OBJECT
 public:
-    explicit MyMainWindow(KDDockWidgets::MainWindowOptions options, QWidget *parent = nullptr);
+    explicit MyMainWindow(const QString &uniqueName, KDDockWidgets::MainWindowOptions options,
+                          const QString &affinityName = {}, // Usually not needed. Just here to show the feature.
+                          QWidget *parent = nullptr);
 
 private:
     void createDockWidgets();

examples/dockwidgets/main.cpp

@@ -58,6 +58,12 @@ int main(int argc, char **argv)
     QCommandLineOption lazyResizeOption("l", QCoreApplication::translate("main", "Use lazy resize"));
     parser.addOption(lazyResizeOption);
 
+    QCommandLineOption multipleMainWindows("m", QCoreApplication::translate("main", "Shows two multiple main windows"));
+    parser.addOption(multipleMainWindows);
+
+    QCommandLineOption incompatibleMainWindows("i", QCoreApplication::translate("main", "Only usable with -m. Make the two main windows incompatible with each other. (Illustrates (MainWindowBase::setAffinityName))"));
+    parser.addOption(incompatibleMainWindows);
+
 #if defined(DOCKS_DEVELOPER_MODE)
     QCommandLineOption noCentralFrame("c", QCoreApplication::translate("main", "No central frame"));
     parser.addOption(noCentralFrame);
@@ -88,11 +94,33 @@ int main(int argc, char **argv)
     if (parser.isSet(lazyResizeOption))
         flags |= KDDockWidgets::Config::Flag_LazyResize;
 
+    if (parser.isSet(incompatibleMainWindows) && !parser.isSet(multipleMainWindows)) {
+        qWarning() << "Error: Argument -i requires -m";
+        return 1;
+    }
+
     KDDockWidgets::Config::self().setFlags(flags);
 
-    MyMainWindow mainWindow(options);
+    MyMainWindow mainWindow(QStringLiteral("MyMainWindow"), options);
+    mainWindow.setWindowTitle("Main Window 1");
     mainWindow.resize(1200, 1200);
     mainWindow.show();
 
+    if (parser.isSet(multipleMainWindows)) {
+        // By default a dock widget can dock into any main window.
+        // By setting an affinity name we can prevent that. Dock widgets of different affinities are incompatible.
+        const QString affinity = parser.isSet(incompatibleMainWindows) ? QStringLiteral("affinity1")
+                                                                       : QString();
+
+        auto mainWindow2 = new MyMainWindow(QStringLiteral("MyMainWindow-2"), options, affinity);
+        if (affinity.isEmpty())
+            mainWindow2->setWindowTitle("Main Window 2");
+        else
+            mainWindow2->setWindowTitle("Main Window 2 (different affinity)");
+
+        mainWindow2->resize(1200, 1200);
+        mainWindow2->show();
+    }
+
     return app.exec();
 }