Android ListView loading control

Question

I have a list that displays a fairly complex layout for each list item and there is noticable lag when I scroll. Yes, I have already put it in AsyncTask and used a View Holder, as suggested here http://lucasr.org/2012/04/05/performance-tips-for-androids-listview/ and http://developer.android.com/training/improving-layouts/smooth-scrolling.html

I think the next thing to try is to load all items in the list when the page is loading (even those that will be off screen), but I cannot seem to find a way to do this. And, yes, I understand that this is a very bad idea and goes against the point of a ListView in a way, if you are expecting many list items. But I should never have more than 20 items in my case and I cannot think of what else to try to make it faster when the user scrolls. So, I would like to be able to control what gets loaded into my ListView adapter, not just take the default of "whatever is visible on the screen at the time".

I think I understand from http://android.amberfog.com/?p=296 and How ListView's recycling mechanism works how the ListView recycling works. But I cannot see a way to load the items that are not currently appearing on the screen, so that it does not have to create a new view when the user scrolls. So my question is: is it possible to load off screen items in the list view so they are not created when the user scrolls? If so, how?

Thanks in advance.

score 1 · Answer 1 · answered Jun 10 '15 at 11:35

Use this listener object to detect if visibleThreshold number of items are still to be rendered in the list. And based on that condition fire your Asynk task to load the data in advance for the rest of elements in list. This kind of technique is used in adding Footer view also.

listenerObject = new AbsListView.OnScrollListener() {
            public void onScrollStateChanged(AbsListView view, int scrollState) {
            }

            public void onScroll(AbsListView view, int firstVisibleItem,
                                 int visibleItemCount, int totalItemCount) {

                int visibleThreshold = 3;
                if (loading == false && (totalItemCount - visibleItemCount) <= (firstVisibleItem + visibleThreshold)) {
                    loading = true;
                    //DO YOUR JOB HERE i.e. your async task
                    // once your async Task is complete make loading as false

                }
            }
        };
lv.setOnScrollListener(listenerObject);

Here lv is the listview. And in case your data is already loaded then you don't have to worry about view creation because it is already taken care of by Android's mechanism to optimise performance.

Android ListView loading control

1 Answers1