Platform and Compiler Notes - Mac OS X

Using native Cocoa panels

Launching native Cocoa panels from within a Qt application can sometimes be problematic. The reason is that Qt's event dispatcher is more flexible than what Cocoa offers, and lets the user spin the event dispatcher (and running QEventLoop::exec) without having to think about whether or not modal dialogs are showing on screen (which is a difference to Cocoa). Therefore we need to do special bookkeeping in Qt to handle this correctly, which unfortunately make mixing in native panels hard. The best way at the moment to do this, is to follow the pattern below, where we post the call to the function with native code rather than calling it directly. Then we know that Qt has cleanly updated any pending event loop recursions before the native panel is shown:

 #include <QtGui>

 class NativeProxyObject : public QObject
 {
     Q_OBJECT
 public slots:
     void execNativeDialogLater()
     {
         QMetaObject::invokeMethod(this, "execNativeDialogNow", Qt::QueuedConnection);
     }

     void execNativeDialogNow()
     {
         NSRunAlertPanel(@"A Native dialog", @"", @"OK", @"", @"");
     }

 };

 #include "main.moc"

 int main(int argc, char **argv){
     QApplication app(argc, argv);
     NativeProxyObject proxy;
     QPushButton button("Show native dialog");
     QObject::connect(&button, SIGNAL(clicked()), &proxy, SLOT(execNativeDialogLater()));
     button.show();
     return app.exec();
 }