[Android]Application use

Make a class extends Application and implement ActivityLifecycleCallbacks:
http://stackoverflow.com/questions/23558986/gcm-how-do-i-detect-if-app-is-open-and-if-so-pop-up-an-alert-box-instead-of-nor/23559146#23559146


Static Way to get Context on android
http://stackoverflow.com/questions/2002288/static-way-to-get-context-on-android/5114361#5114361


How to declare global variables in Android
http://stackoverflow.com/questions/708012/how-to-declare-global-variables-in-android/708317#708317


survey Application class and dealing with Singleton,get the article and code resource from Singleton