Section gap is gone when expand the last item of section

[steventxc]

as above describe, when the section contains a expandable item at last, expand it, the gap is gone, but collapse it, the gap is visible as normal. it's weird. any suggestion for it ? thx.

[steventxc]

collapsed:

expanded:

[davideas]

Could you call invalidateItemDecorations(delay) when expanding?
The RV should apply the decoration to the current view during a layout pass, but is calculated and applied if the next item is a header. So, if we insert a new view type the decoration is lost.

[steventxc]

@davideas I'm not sure where to insert invalidateItemDecorations(delay) method.
i try insert code these place:

1. in ExpandableViewHolder:

   @Override
   protected boolean shouldNotifyParentOnClick() {
       return true;
   }
   
   @Override
   protected void expandView(int position) {
       mAdapter.invalidateItemDecorations(100);
       super.expandView(position);
   }
   

2. in AbstractExpandableItem :

    @Override
    public void bindViewHolder(FlexibleAdapter adapter, ES_ViewHolder holder, int position, List<Object> payloads) {
    	holder.tv_userName.setText(userName);
    	holder.tv_suggestion.setText(suggestion);
    	holder.iv_status.setImageResource(iconRes);
    
    	adapter.invalidateItemDecorations(100);
    }
   

3. in Fragment when init adapter:

   List<ISectionable> list = new ArrayList<>();
   
   // section 1
   FDHeader header1 = new FDHeader(1, "Header 1");
   FDEatableSection section1 = new FDEatableSection(header1, "section1_1",
                       null, R.drawable.ic_eat_half);
   section1.addSubItem(new FDEatableSubItem(0, "section sub 1_1_1"));
   list.add(section1);
   
   // section 2
   FDHeader header2 = new FDHeader(2, "Header 2");
   
   FDEatableSection section2_1 = new FDEatableSection(header2, "section2_1", 
                       null, R.drawable.ic_eat_half);
   section2_1.addSubItem(new FDEatableSubItem(1, "section sub 2_1_1"));
   section2_1.addSubItem(new FDEatableSubItem(2, "section sub 2_1_2"));
   list.add(section2_1);
   
   // ....
   
   mAdapter = new FlexibleAdapter<ISectionable>(list,
                       FoodDetailFragment1.this, true);
   
   mAdapter.setDisplayHeadersAtStartUp(true)
       .setMinCollapsibleLevel(1) 
       .setAutoCollapseOnExpand(true)
       .expandAll(0); 
   
   
   recyclerView.setAdapter(mAdapter);
   recyclerView.addItemDecoration(new FlexibleItemDecoration(_mActivity)
                       .withSectionGapOffset(24));
   
   // i'm not sure this is necessary             
   mAdapter.invalidateItemDecorations(100);
               
   

but all above are not work. :(

especially the third point, some items will expand at the beginning, how could i handle the gap?

[davideas]

@steventxc, try 1st point after the super() call since the expand occurs inside there.

[steventxc]

@davideas i followed your instruction, but it was not work.
so i put my code in this address, am i do something wrong?

[davideas]

@steventxc, the FDSubItem is not a ISectionable type, when I created the gap, it was only for 1 level of section with items of type ISectionable.
But now I need more time, I'm too busy in these days.

[steventxc]

@davideas Thanks your time and help.
It's work when I implement the ISectionable interface.

[davideas]

@steventxc, but which header do you assign? I tried and when no header is assigned it works nicely, but it will have an impact for your sticky header if activated, it won't work as expected.
I will have to find another way to create the gap. please keep this issue open.

[davideas]

This will be the condition in FlexibleItemDecoration to apply section gap from the next version:

// IMPORTANT: the check must be done on the BOTTOM of the section,
// otherwise the sticky header will jump!
if (flexibleAdapter.isHeader(nextItem)) { // = nextItem instanceof IHeader
    Log.v("applySectionGap position=%s", position);
    if (orientation == RecyclerView.VERTICAL) {
        outRect.bottom += mSectionOffset;
    } else {
        outRect.right += mSectionOffset;
    }
}
if (position >= adapter.getItemCount() - mSectionGapOnLastItem) {
    Log.v("applySectionGapOnLastPosition position=%s", position);
    if (orientation == RecyclerView.VERTICAL) {
        outRect.bottom += mSectionOffset;
    } else {
        outRect.right += mSectionOffset;
    }
}

But for IExpandable, we will have always to invalidate the item decoration when expanding and collapsing!

So we don't need ISectionable anymore for subItems in expandables.

[davideas]

I was smarter and I was able to identify the header of the section anyway. That's why sticky header works if you don't apply any header. However, i think is not good to implement ISectionable just to have the gap, the interface covers another purpose.

[steventxc]

@davideas as you said above, in my project, i never assign any header for subitem, just implement ISectionable, it works fine :)
thanks for your excellent and also SMART job! 😁