The run() member function is executed in a different thread, rather than the thread where QNetworkRequestManager object was created.
This kind of different-thread problems happen all the time with Qt when you use multiple threads. The canonical way to solve this problem is to use signals and slots.
Create a slot in the object where QNetworkRequestManager belongs to, create a signal in ResultThread and connect both of the somewhere, the constructor of ResultThread would be a good place.
The code which is currently in ResultThread::run() goes to the new slot, and is replaced by a emit(yourSignal()). If necessary send a pointer to your ResultThread as a parameter with your emit function to gain access to member functions/variables.