keep Scroll position with every refresh in list view

Question

I set a timer in my app, I could get some information from a web service and resulted in a list view to display. Now my problem is that every time the timer runs, scroll back to the beginning ...

how can i keep Scroll position with every refresh in list view ?

part of my code:

runOnUiThread(new Runnable() {
    public void run() {
        /**
         * Updating parsed JSON data into ListView
        * */
        ListAdapter adapter = new SimpleAdapter(DashboardActivity.this, 
                                                all_chat, 
                                                R.layout.list_item, 
                                                new String[] { TAG_FULLNAME,
                                                               TAG_DATE, 
                                                               TAG_MESSAGE }, 
                                                new int[] { R.id.fullname,
                                                            R.id.date, 
                                                            R.id.message }
                                               );
        // updating listview
        setListAdapter(adapter);
    }
});

TNx.

Answer 1

I had the same issue, tried a lot of things to prevent the list from changing its scroll position, including:

android:stackFromBottom="true"
android:transcriptMode="alwaysScroll"

and not calling listView.setAdapter(); None of it worked until I found this answer:

Which looks like this:

// save index and top position
int index = mList.getFirstVisiblePosition();
View v = mList.getChildAt(0);
int top = (v == null) ? 0 : (v.getTop() - mList.getPaddingTop());

// ...

// restore index and position
mList.setSelectionFromTop(index, top);

Explanation:

ListView.getFirstVisiblePosition() returns the top visible list item. But this item may be partially scrolled out of view, and if you want to restore the exact scroll position of the list you need to get this offset. So ListView.getChildAt(0) returns the View for the top list item, and then View.getTop() - mList.getPaddingTop() returns its relative offset from the top of the ListView. Then, to restore the ListView's scroll position, we call ListView.setSelectionFromTop() with the index of the item we want and an offset to position its top edge from the top of the ListView.

Answer 2

Do not call setAdapter(). Do something like this:

ListAdapter adapter; // declare as class level variable

runOnUiThread(new Runnable() {
    public void run() {
        /**
         * Updating parsed JSON data into ListView
         */
        if (adapter == null) {
            adapter = new SimpleAdapter(
                    DashboardActivity.this, all_chat, R.layout.list_item, new String[]{TAG_FULLNAME, TAG_DATE, TAG_MESSAGE},
                    new int[]{R.id.fullname, R.id.date, R.id.message});
            setListAdapter(adapter);
        } else {
            //update only dataset   
            allChat = latestetParedJson;
            ((SimpleAdapter) adapter).notifyDataSetChanged();
        }
        // updating listview
    }
});