How to save and restore the state of an ExpandableListView in Android?

Question

Is it possible to save and restore the state (which items are collapsed and which not) of an ExpandableListView in Android?

If it is possible, how can I do that?

Answer 1

I came across this very same question and found a better answer. I have a fragment and use the onSaveInstanceState and onViewStateRestored to save and restore the ExpandableListView.

Here I save the state of the list

@Override
public void onSaveInstanceState( @NonNull Bundle outState )
{
    super.onSaveInstanceState( outState );

    ExpandableListView expandable = getView() != null ? getView().findViewById( R.id.expandable ) : null;
    if( expandable != null )
    {
        int groupsCount = expandable.getExpandableListAdapter()
                                    .getGroupCount();
        boolean[] groupExpandedArray = new boolean[groupsCount];
        for( int i = 0; i < groupsCount; i += 1 )
        {
            groupExpandedArray[i] = expandable.isGroupExpanded( i );
        }
        outState.putBooleanArray( "groupExpandedArray", groupExpandedArray );
        outState.putInt( "firstVisiblePosition", expandable.getFirstVisiblePosition() );
    }
}

And here I restore it when it is needed

@Override
public void onViewStateRestored( @Nullable Bundle savedInstanceState )
{
    super.onViewStateRestored( savedInstanceState );
    if( savedInstanceState != null )
    {
        boolean[]          groupExpandedArray   = savedInstanceState.getBooleanArray( "groupExpandedArray" );
        int                firstVisiblePosition = savedInstanceState.getInt( "firstVisiblePosition", -1 );
        ExpandableListView expandable           = getView() instanceof ViewGroup ? getView().findViewById( R.id.expandable ) : null;
        if( expandable != null && groupExpandedArray != null )
        {
            for( int i = 0; i < groupExpandedArray.length; i++ )
            {
                if( groupExpandedArray[i] )
                    expandable.expandGroup( i );
            }
            if( firstVisiblePosition >= 0 )
                expandable.setSelection( firstVisiblePosition );
        }
    }
}