Question

I have a little problem about needing Activity/Application everywhere…
More precisely I have classes defined like this:

public class MyApp extends Application {

     private static Activity currentActivity;
     private static MyApp instance;

     @Override
     public void onCreate() {
         super.onCreate();
         instance = this;
     }

     public static void setCurrentActivity(Activity activity) {
         currentActivity = activity;
     }
}

And I have an Extended activity like this:

public class MyActivity extends Activity {

       ....

       @Override
       public void onResume() {
          super.onResume();
          MyApp.setCurrentActivity(this);
       }


       ....

       @Override
       public void onDestroy() {
          super.onDestroy();   
          MyApp.setCurrentActivity(null);  // for nullifying static reference

       }
 }

My questions are:

1. Is the above code snippet fair ?
2. Should I use super.onDestroy(); after the MyApp.setCurrentActivity(null); to verify that activity is not reffered and destroyed succesfully?
3. And most important, what about static reference instance? where can I nullify it to not prevent from GC ?

Thanks.

Answer 1

1. Is the above code snippet fair ?

Nope. The biggest problem is in MyActivity.onDestroy(). This can be called at any time when the activity is no longer in use (ie: after it has finished). If you null out currentActivity in onDestroy() you will not be clearing the reference to MyActivity, you will be clearing the reference to whatever activity happens to be currently active at the moment. I you really want to have currentActivity point to the current activity, the best you can do is something like this:
@Override
public void onPause() {
super.onPause();
if (MyApp.getCurrentActivity() == this) {
MyApp.setCurrentActivity(null);
}
}

Also, be aware that there is a small window between onPause() of an activity and onResume() of the next activity so that it is possible that currentActivity will be null during this time. Watch out for that!

Should I use super.onDestroy(); after the
MyApp.setCurrentActivity(null); to verify that activity is not
reffered and destroyed succesfully?

See my comment above. You cannot null out this reference in onDestroy().

And most important, what about static reference instance? where can I
nullify it to not prevent from GC ?

You don’t need to. There is only ever one instance of MyApp created and it lives for as long as your process exists. When Android doesn’t need your process anymore it just kills the process, which will clean up everything automagically.