Why is the ContentObserver called multiple times?

I have following ContentObserver implementation for receiving and writing SMS, but it is called multiple times.

Code:

public class SMSObserverActivity extends Activity {
    protected MyContentObserver observer = null;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        String url = "content://mms-sms/";
        Uri uri = Uri.parse(url);
        observer = new MyContentObserver(new Handler());
        getContentResolver().registerContentObserver(uri, true, observer);
    }

    @Override
    protected void onDestroy(){
        super.onDestroy();

        getContentResolver().unregisterContentObserver(observer);
    }

    class MyContentObserver extends ContentObserver {
        ContentValues values = new ContentValues();
        Handler handler;

        public MyContentObserver(Handler handler){
            super(handler);
            this.handler = handler;
        }

        @Override
        public boolean deliverSelfNotifications(){
            return false;
        }


        @Override
        public void onChange(boolean arg0){
            super.onChange(arg0);

            Log.v("SMS", "Notification on SMS observer");
            values.put("status", 5);
            Message msg = new Message();
            msg.obj = "xxxxxxxxxx";
            int threadId = 0;
            handler.sendMessage(msg);

            Uri uriSMSURI = Uri.parse("content://sms/");
            Cursor cur =
                    getContentResolver().query(uriSMSURI, null, null, null,
                            null);
            cur.moveToNext();
            Log.e("sms", cur.getString(4)+" "+cur.getString(11));
        }
    }
}

Manifest:

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.test"
    android:versionCode="1"
    android:versionName="1.0">
    <uses-sdk android:minSdkVersion="8" />
    <uses-permission android:name="android.permission.READ_SMS"></uses-permission>
    <uses-permission android:name="android.permission.WRITE_SMS"></uses-permission>

    <application android:icon="@drawable/icon" android:label="@string/app_name">
        <activity android:name=".SMSObserverActivity"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

    </application>
</manifest>

Why is it called multiple times?

EDIT:
There was the idea that the problem is caused by the missing unregisterContentObserver, but it makes no difference.

This is occurring because you are registering your content observer for the entire SMS database. So your content observer gets notified each time a table entry in the database gets updated.

In this case when a message is sent for example around 7 tables entries get updated so your content observer gets notified 7 times.

Since I'm only interested if a message is sent I've changed to only observe the queued messages and this means my observer always gets notified exactly three times so I have implemented code to protect against that.

There are likely to be some other issues such as multi recipient or multi part messages but the basics work so far.