You need to pass a reference to an object that implements your listener to your 'SyncData' class when you create it. Presumably, at the moment in your LoginPage you have something that looks like this.
It may be possible that you dialog object gets null so instead.
I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.