Question

well most of us familiar with this pattern:

   public class MySingeltone {

    public String mSomeReferenceTypeData;
    public int mSomeValueTypeData;

    private static MySingeltone mInstance;

    private MySingeltone() {

    }

    public static MySingeltone getInstance() {
        if (mInstance == null) {
            mInstance = new MySingeltone();
        }

        return mInstance;
    }
 }

my problem is that I’ve found recently that the mInstance don’t equal null after activity using him been destroyed, or when the whole application suppose to be clause, for example:

public class SomeActivity extends Activity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        MySingeltone mySingeltone = MySingeltone.getInstance();
        mySingeltone.mSomeReferenceTypeData = "some value";
    }
}

when launching “SomeActivity” next time after closing the whole applications running activities (say 10 seconds after..) the mInstance still holds the same reference, with the same values on his fields.

why does it happening?

what am I missing?

when android garbage collecting static members belongs to application?

Answer 1

Since “mInstance” is a static variable it will not get null when you close your application. Closing of application doesn’t means that your application got destroyed.

Also there is no concept of Closing your Android app. If you get out of your app it will not get destroyed at the same time. Android OS handles it internally when to close the app when it is no more in use. In case of memory shortage when android decides to destroy the app then this static variable will also got null.