Alternate view for an empty group in an expandableList

Question

The question is simple, but I can't make it work. I have a expandable list with 3 header, they can be either populated or empty.

I wish to show a simple textview when you expand a group that is empty, I've been looking for a while but nothing seems to work. i can't use setEmpty() because this will only work if all the groups are empty.

I found a similar thread here: ExpandableListView - empty group message

If i try to do as the accepted answer suggested, so:

@Override
public int getChildrenCount(int groupPosition) {
    if(this._listDataChild.get(this._listDataHeader.get(groupPosition))
            .size() != 0){
        return this._listDataChild.get(this._listDataHeader.get(groupPosition))
                .size();        
    }
    return 1;
}

I get an error when i try to expand the empty group ... And I don't think this would work anyway, for instance what will happen if I have a group with 1 child, will it be considerated as empty ??

EDIT:

Ok I solved this by always having an null object at the first place in mys child list, then when getchildrencount returns 1, I know it's actually empty and so I call the empty case of the switch. In the populated case of the switch i always hide the first element, this might not be the cleanest way to do this, but this works.

Answer 1

If you are using different layouts whether they are populated or empty, you can distinguish by overriding getChildType or getGroupType like this

private static final int CHILD_TYPE_COUNT = 2;

@Override
public int getChildType(int groupPosition, int childPosition) {
    if(obj.isEmpty())
        return 0;
    else if(obj.isPopulated)
        return 1;
}

@Override
public int getChildTypeCount() {
    return CHILD_TYPE_COUNT;
}

Then you can use the corresponding layout to populate. I suggest you also use the ViewHolder-Pattern

static class PopulatedViewHolder {
    //declare the elements of a populated view here
}

static class EmptyViewHolder {
    //declare the elements of an empty view here
}


@Override
public View getChildView(final int groupPosition, final int childPosition, boolean isLastChild,
        View convertView, ViewGroup parent) {

    EmptyViewHolder emptyViewHolder = null;
    PopulatedViewHolder populatedViewHolder = null;

    //check if the type of your view is populated or empty and use the corresponding layout
    int type = getChildType(groupPosition, childPosition);

    if (convertView == null || (type == 0 && (convertView.getTag()) instanceof PopulatedViewHolder) || (type == 1 && (convertView.getTag()) instanceof EmptyViewHolder)) {
        LayoutInflater inflater = (LayoutInflater)context
                .getSystemService(Context.LAYOUT_INFLATER_SERVICE);

        switch(type){
            case 0:
                //type is empty
                emptyViewHolder =  new EmptyViewHolder();
                convertView = inflater.inflate(R.layout.empty_layout,
                        parent, false);

                //...initialize your viewcomponents of the populated layout here...

                convertView.setTag(emptyViewHolder);
                break;
            case 1:
                //populated
                populatedViewHolder = new PopulatedViewHolder();
                convertView = inflater.inflate(
                        R.layout.populated_layout, parent, false);

                //...initialize your viewcomponents of the populated layout here...

                convertView.setTag(populatedViewHolder);

                break;
        }
    }
    else {
        switch (type) {
            case 0:
                emptyViewHolder = (EmptyViewHolder)convertView.getTag();
                break;

            case 1:
                PopulatedViewHolder = (PopulatedViewHolder)convertView.getTag();
                break;
        }
    }

    switch(type){
        case 0:
            //empty
            //set the values of your empty view here

            break;
        case 1:
            //populated
            //set the values of your populated view here

            break;
     }

    return convertView;
}