sending text from editText to ListView (2 activities)

sending text from editText to ListView (2 activities)

i am new to Andriod and programming. i am trying to make a to do list app,
which will contain a listView, Button(add) in the main layout. when i
click add i want it to go to another activity which will contain a
editText and a add button. when i click the add button i want to update
the list in my main activity. Now i was able to get the information from
the second activity but when i try to add it in my list it over writes it.
How can i update my list as soon as my main activity appears again.
Here's what i have so far :
MainActivity class :
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
add = (Button) findViewById(R.id.bAdd);
list = (ListView) findViewById(R.id.lvList);
addItems(); // i think this is the error but i dont know how to fix it.
alList = new ArrayList<String>();
aaList = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, alList);
list.setAdapter(aaList);
}
public void clickAdd(View v) { //when clicking the add button(add)
Intent intent = new Intent(MainActivity.this, AddItem.class);
startActivity(intent);
}
private void addItems(){
String s = getIntent().getStringExtra("item");
aaList.add(s);
aaList.notifyDataSetChanged();
}
AddItem class :
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.add_layout);
et = (EditText) findViewById(R.id.etAdd);
bt = (Button) findViewById(R.id.badd);
}
public void add(View v){ //when clicking the add button(bt)
edit = et.getText().toString();
Intent intent = new Intent(AddItem.this, MainActivity.class);
intent.putExtra("item", edit);
startActivity(intent);
}
Can you please tell me where and why i am going wrong? Thank You