Listview + BaseAdapter - 如何通知单项的变更？

Question

I have a list view fed by BaseAdapter.

When something changes in data, I call BaseAdapter.notifyDataSetChanged. All works fine.

Now I wonder, if I change some tiny detail in some list item, is there some optimized way to update view of single item if it's displayed on screen ? I suppose that notifyDataSetChanged blindly rebuilds views of all visible items in list, which is not optimal if trivial change in item happens.

Answer 1

No, I guess it's not possible unless you implement your own ListView class extension. Here there is the source code for setAdapter() .

You will see, the ListView only registers itself as observer using mAdapter.registerDataSetObserver(mDataSetObserver); And a DataSetObserver provides no means to notify about a change at a certain position.

However it might not be necessary to notify about updates of certain items, because as far as I know, a ListView only renders and updates the items currently seen on the screen so, no optimization should be necessary here.

Answer 2

Yes, there is way. Assuming I can identify list item, for example by assigning View.setTag to it to some value, I can iterate list items and rebind only one list item if desired, or even update only some sub-view of the item.

It's simple and relatively cheap (linear search):

for(int i = list.getChildCount(); --i>=0; ){
   View v = list.getChildAt(i);
   Object id = v.getTag();
   if(id==myId){
      updateListItem(id, v);
      break;
   }
}

where myId is some ID of item I want to update, and updateListItem makes desired changes on the list item. Proved, and working fine and very efficiently.