Android: How to correctly use NotifyDataSetChanged with SimpleExpandableListAdapter?

Question

I am struggeling updating my ExpandableListView via NotfiyDataSetChanged.

I am downloading some data from a webserver, which is displayed correctly in my ExpandableListView.

By clicking on a child item, the user gets displayed a dialog where he can change some value. This value is supposed to show up in the ExpandableListView, so I change the background data in my class and call NotifyDataSetChanged(). This works fine for the child items, until I send off a new request to the Webserver. Then, neither in my downloading function nor my local change function, NotifyDataSetChanged() works.

As I want to change some group item content as well (after the dialog), I also change the background data of my groups, too. However, while NotifyDataSetChanged() works at least a few times for the child items, it doesn't at all show any effect on the group items.

I have checked with debugger & log.d() if my background data really changes, but it does.

Looking into this question and this thread, I believe I am using notifyData... wrong. But I can't figure out how it's supposed to work. Only useful function I found was registerDataSetObserver(observer), but I wasn't sure how to use this as well. :/

Here is my code. There might be some small errors, as I tried to strip it down to the necessary parts.

@SuppressWarnings("rawtypes")
private List children;
@SuppressWarnings("rawtypes")
private List groups;
private SimpleExpandableListAdapter expListAdapter;


/*download from webserver*/
void function1()
{
    groups = new ArrayList();
    children = new ArrayList();

    */go through a list I downloaded*/
    for (...)
    {
        HashMap groupMap = new HashMap();
        groupMap.put(groupName, downloadedList.getName());
        groupMap.put(groupRate, downloadedList.getMatchrate() + getString(R.string.matchrate));
        groups.add(groupMap);

        ArrayList childList = new ArrayList();
        HashMap childMap;

        */go through a sublist and fill child Map accordingly*/
        for (...)
        {
            childMap = new HashMap();
            childMap.put(...);
            childList.add(childMap);
        }

        children.add(childList);

    }

    if (expListAdapter == null)
    {
        expListAdapter = new SimpleExpandableListAdapter(KnBDiagMan.this, groups, 
                R.layout.xlist_group_item, 
                new String[]
                { groupName, groupRate }, //private final static String components of my activity
                new int[]
                { R.id.title, R.id.rate }, 
                children, 
                R.layout.xlist_child_item, 
                new String[]
                { childName, childValue }, 
                new int[]
                { R.id.child_title, R.id.child_value } 
        )
        {
            @Override
            public View getChildView(int groupPosition, int childPosition, boolean isLastChild, View convertView, ViewGroup parent)
            {
                /*change of the text color of R.id.child_value's depending on content*/
            }
        };

        setListAdapter(expListAdapter);
    }
    else
    {
        expListAdapter.notifyDataSetChanged();
    }
}

/*change after Dialog*/
void function2()
{
    String savedChildName = (String) ((HashMap) ((ArrayList) children.get(groupPos)).get(childPos)).get(childName);

    for (int i = 0; i < children.size(); ++i)
    {
        List secondLevel = (ArrayList) children.get(i);

        for (int j = 0; j < (secondLevel.size()); ++j)
        {
            HashMap map = (HashMap) secondLevel.get(j);
            String compareName = (String) map.get(childName);

            if (compareName.contentEquals(savedChildName))
            {
                HashMap newMap = new HashMap();
                newMap.put(childName, savedChildName);
                newMap.put(childValue, newValue);
                secondLevel.set(j, newMap);
            }
        }
    }

    List newGroups = new ArrayList();

    for(int i = 0; i < groups.size(); ++i)
    {
        String savedGroupName = (String) ((HashMap) groups.get(i)).get(groupName);
        HashMap groupContent = new HashMap();
        groupContent.put(groupName, savedGroupName);
        groupContent.put(groupRate, getString(R.string.newString));
        newGroups.add(groupContent);
    }

    groups = newGroups;

    expListAdapter.notifyDataSetChanged();
}

Update: Everything is working as intented if I create a new SimpleExpandableListAdapter instead of calling notifyDataSetChanged. However, I am sure this can't be the solution. What would be the point in using an Adapter at all?

Answer 1

You're replacing your local reference to the SimpleExpandableListAdapter's data objects with a new reference... Instead of:

List newGroups = new ArrayList();
...
groups = newGroups;

Try:

groups.clear();

// Add items here
...

expListAdapter.notifyDataSetChanged();