You might want to look at src/gui/util/qsystemtrayicon_mac.mm for some usage of NSApplication.

Thanks for the reply, If i want to use Qt Class function in Cocoa class, then how can i use it?

That depends on the class and method. Some of them (most notable the GUI classes and many QObject derived classes) need a Qt event loop running (which is usually achieved by starting exec() on a QApplication). Others do not depend on this (e.g. QString, the container classes, the XML classes) and can be used directly.

I want to call QtGui class function in cocoa class,, how can i call Qtcode class function in cocoa class, can you explain it with an example?

Sorry, I have never used Qt this way before, so I cannot provide a sample code.

Ok, not an issue, i will try to do something else.