Question

My project simplify as below:
First, I use application method Data.java to save data.
It contain the data:

private ArrayList<String> data = new ArrayList<String>();
public int getsize() {
return this.data.size();
}
public String getdata(int i) {
return this.data.get(i);
}
public void adddata(String s) {
return this.data.add(s);
}

My AActivity class onCreate as below:

Data d = (Data)this.getApplication();
String test = new String[d.getsize()];
for(i = 0; i < d.getsize(); i++) {
test[i] = d.getdata(i);
}
//to show in list
DataAdapter = new DataAdapter (this, test);
setListAdapter(DataAdapter);

And when button is click, startActivity the BActivity class.
In BActivity class, the code as below:

Data d = (Data)this.getApplication();
d.adddata("newdata");
finish();

And AActivity class onResume() as below:

@Override
public void onResume(){
super.onResume();
this.DataAdapter.notifyDataSetChanged();
}

But why the list is not update?
I confirm the data has be save.

My DataAdapter:

public DataAdapter(Context ctxt, String[] d) {
this.data = new String[d.length];
myInflater = LayoutInflater.from(ctxt);
int i;
for(i = 0; i < d.length; i++) {
data[i] = d[i];
}
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ViewTag viewTag;
if(convertView == null) {
convertView = myInflater.inflate(R.layout.row_bookmark_list, null);
viewTag = new ViewTag((TextView)convertView.findViewById(R.id.tv));
convertView.setTag(viewTag);
}
else {
viewTag = (ViewTag) convertView.getTag();
}
viewTag.tv.setText(data[position]);
}
class ViewTag {
TextView tv;
public ViewTag(TextView t) {
this.tv = t;
}
}

Answer 1

Add your new data directly to the adapter not to ‘d’. The adapter keeps its own internal data which means that whatever changes you apply to your ‘d’ has no impact on the adapter.

For example:

List<String> itemsList = new ArrayList<String>();
ArrayAdapter aa = new ArrayAdapter(..., itemsList);
...
itemsList.add("new item"); --> wrong!
aa.notifyDataSetChanged(); --> nothing changes, you wrongly added the item to itemsList

you have to deal directly with the adapter:

aa.add("new item");          --> correct
aa.notifyDataSetChanged();   --> the adapter will reflect the change