Save and restore expanded/collapsed state of an ExpandableListActivity

Question

I have an ExpandableListActivity (using a SimpleCursorTreeAdapter) which starts another activity when the user clicks on a child-element. When pressing the back-button in the new activity all the list-items are collapsed again. How do I save the expanded state of the ExpandableListActivity and restore it again.

I already tried to implemented onSaveInstanceState() and onRestoreInstanceState() like this...

@Override
protected void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    Parcelable listState = getExpandableListView().onSaveInstanceState();
    outState.putParcelable("ListState", listState);
}


@Override
protected void onRestoreInstanceState(Bundle state) {
    super.onRestoreInstanceState(state);
    Parcelable listState = state.getParcelable("ListState");
    getExpandableListView().onRestoreInstanceState(listState);
}

...but onRestoreInstanceState() gets never called. I also tried to restore the state in the onCreate() method but it isn't called as well:

if (savedInstanceState != null) {
    Parcelable listState = savedInstanceState.getParcelable("ListState");
    getExpandableListView().onRestoreInstanceState(listState);
}

I am doing something similar HERE http://stackoverflow.com/questions/10611927/simplecursortreeadapter-and-cursorloader — Etienne Lawlor, May 16 '12 at 07:22
Beware of setting the adapter again when returning to the previous activity. Setting the adapter anew will collapse the list. — jayeffkay, May 08 '13 at 10:30

Tom · Accepted Answer · 2010-11-15T16:53:15.140

Unfortunately the expanded state always resets whenever the focus is lost and onCreate() is not called when it gets the focus again but onStart(). So my workaround for now is to manually store the IDs of all expanded items and expand them in onStart() again. I implemented a subclass of ExpandableListActivity to reuse the behavior.

public class PersistentExpandableListActivity extends ExpandableListActivity {
    private long[] expandedIds;

    @Override
    protected void onStart() {
        super.onStart();
        if (this.expandedIds != null) {
            restoreExpandedState(expandedIds);
        }
    }

    @Override
    protected void onStop() {
        super.onStop();
        expandedIds = getExpandedIds();
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        this.expandedIds = getExpandedIds();
        outState.putLongArray("ExpandedIds", this.expandedIds);
    }

    @Override
    protected void onRestoreInstanceState(Bundle state) {
        super.onRestoreInstanceState(state);
        long[] expandedIds = state.getLongArray("ExpandedIds");
        if (expandedIds != null) {
            restoreExpandedState(expandedIds);
        }
    }

    private long[] getExpandedIds() {
        ExpandableListView list = getExpandableListView();
        ExpandableListAdapter adapter = getExpandableListAdapter();
        if (adapter != null) {
            int length = adapter.getGroupCount();
            ArrayList<Long> expandedIds = new ArrayList<Long>();
            for(int i=0; i < length; i++) {
                if(list.isGroupExpanded(i)) {
                    expandedIds.add(adapter.getGroupId(i));
                }
            }
            return toLongArray(expandedIds);
        } else {
            return null;
        }
    }

    private void restoreExpandedState(long[] expandedIds) {
        this.expandedIds = expandedIds;
        if (expandedIds != null) {
            ExpandableListView list = getExpandableListView();
            ExpandableListAdapter adapter = getExpandableListAdapter();
            if (adapter != null) {
                for (int i=0; i<adapter.getGroupCount(); i++) {
                    long id = adapter.getGroupId(i);
                    if (inArray(expandedIds, id)) list.expandGroup(i);
                }
            }
        }
    }

    private static boolean inArray(long[] array, long element) {
        for (long l : array) {
            if (l == element) {
                return true;
            }
        }
        return false;
    }

    private static long[] toLongArray(List<Long> list)  {
        long[] ret = new long[list.size()];
        int i = 0;
        for (Long e : list)  
            ret[i++] = e.longValue();
        return ret;
    }
}

Maybe someone has a better solution though.

score 2 · Answer 2 · answered Apr 21 '13 at 19:26

2

This should work

Parcelable state = exercisesList.onSaveInstanceState();
exercisesList.setAdapter(....);
exercisesList.onRestoreInstanceState(state);

answered Apr 21 '13 at 19:26

Sergei Ledvanov

2,131
6
29
52

1

The accepted answer is completely unnecessary. This is the proper way. – JanithaR Aug 10 '17 at 09:35

score 0 · Answer 3 · answered Nov 15 '10 at 13:16

0

Try this. It will solve the problem, partly

yourlist.setSaveEnabled(true);

answered Nov 15 '10 at 13:16

user479211

1,544
1
12
13

Unfortunately this doesn't change anything. – Tom Nov 15 '10 at 14:05
It works only for change orientation of a screen (if data of adapter will not be reloaded after change orientation of a screen) – user479211 Nov 15 '10 at 14:29

Save and restore expanded/collapsed state of an ExpandableListActivity

3 Answers3

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