The sqlite database insert duplicated data

I got the data from webservice and insert them to database in activity onCreate() function. the code is as below:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    setContentView(R.layout.contact_person);

    RunningService runningService = new RunningService();
    runningService.insert(staff);
    initView();
}

And the the code of insert() is as below:

public void insertAllStaff(Staff staff){
    ContentValues values = new ContentValues();
    values.put("name", staff.getName());
    Uri uri = contentResolver.insert(CONTENT_URI, values);
}

Every time that I go into this activity, it will insert data to database, the data are the same.

Is there a method that I can go into this activity and it doesn't insert the same data to database?