activity管理

 public class MainApp extends Application {

      private static ArrayList<WeakReference<Activity>> activitys;
      public volatile static MainApp instance;
     @Override
     public void onCreate() {
         // TODO Auto-generated method stub
         super.onCreate();
      }

     public MainApp() {
         // TODO Auto-generated constructor stub
     }
     public static MainApp getInstance(){
         if(instance==null){
             synchronized (MainApp.class) {
                 if(instance==null){
                     instance=new MainApp();
                 }
             }
         }
         return instance;
     }

         public static void addActivity(Activity context) {
             if(activitys==null){
                 activitys=new ArrayList<WeakReference<Activity>>();
             }
             activitys.add(new WeakReference<Activity>(context));
         }

         public static void removeActivity(Activity activity) {

             if(activity!=null){

                 activitys.remove(new WeakReference<Activity>(activity));
                 activity.finish();
                 activity=null;
             }

         }

         public static void finishAllActivity() {
             Activity activity;
             for (int i = activitys.size() - 1; i >= 0; i--) {
                 activity = activitys.get(i).get();
                 if (activity != null && !activity.isFinishing()) {
                     activity.finish();
                 }
             }
             activitys.clear();
         }