在有一些場景下，需要我們在app從後臺程序到前臺程序的切換過程中，做一些操作，如展示一個公司廣告頁面等等情況。這個時候，我們可以在我們的Application中來監聽當前App的狀態，Google已經給我們封裝好了方法:

public class MyApplication extends Application {
    @Override
    public void onCreate() {
        super.onCreate();
        Log.i("justh","application oncreate");

        registerActivityLifecycleCallbacks(new
 
 ActivityLifecycleCallbacks() {
            @Override
            public void onActivityCreated(Activity activity, Bundle savedInstanceState) {
                Log.i("justh","onActivityCreated");
            }

            @Override
            public void onActivityStarted(Activity activity) {
                Log.w("justh"
 
,"onActivityStarted");
            }

            @Override
            public void onActivityResumed(Activity activity) {
                Log.e("justh","onActivityResumed");
            }

            @Override
            public void onActivityPaused(Activity activity) {
                Log.i("justh"
 
,"onActivityPaused");
            }

            @Override
            public void onActivityStopped(Activity activity) {
                Log.i("justh","onActivityStopped");
            }

            @Override
            public void onActivitySaveInstanceState(Activity activity, Bundle outState) {
                Log.i("justh","onActivitySaveInstanceState");
            }

            @Override
            public void onActivityDestroyed(Activity activity) {

            }
        });
    }
}

對，就是這個registerActivityLifecycleCallbacks方法，具體的生命週期該呼叫的方法應該就不需要過多說明了吧，嘿嘿!