Q_OBJECT is used by the MOC system to produce the code you need for the signals. My best guess would be that you are not included the MOC generated files in your project (the CPP files which it generates).
How you do this greatly depends on your build system (CMake, QMake, AUtomake, MSVC) but you should refer to the tutorial with QMake first.
That is, the undefined reference to vtable is the error I sometimes get when I forget to update my Cmake files and have a Q_OBJECT.
Also, your ctor for MyApp is wrong, the signature must be:
MyApp( int & argc, char** argv );
The & is important should you ever use command-line parameters.
