how to use ContentObserver..?

Question

I'm very new to this stuff and could't find an appropriate answer. I did something by myself, i don't know to what extent i'm rite. and its not working.

package com.aqui.observer;

import android.app.Activity;
import android.os.Bundle;
import android.os.Handler;
import android.provider.ContactsContract;

    public class ObserverActivity extends Activity {
        private MyObserver observer;

        /** Called when the activity is first created. */
        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.main);
            observer = new MyObserver(new Handler());
            getContentResolver().registerContentObserver(ContactsContract.Data.CONTENT_URI, true, observer);
        }

    @Override
    protected void onStop() {
        super.onStop();
        getContentResolver().unregisterContentObserver(observer);
    }

    @Override
    protected void onStart() {
        super.onStart();
         getContentResolver().registerContentObserver(ContactsContract.Data.CONTENT_URI, true, observer);
    }
}

and this is my observer.

package com.aqui.observer;

import android.database.ContentObserver;
import android.os.Handler;
import android.util.Log;

public class MyObserver extends ContentObserver{

    public MyObserver(Handler handler) {
        super(null);
    }
@Override
public void onChange(boolean selfChange) {
    super.onChange(selfChange);
    Log.e("CHANGEsTrappedSuccessfully", "YEAH..YEAh");
}
}

thank you in advance.