android - How to selectively decorate RecyclerView items

Question

I am creating a subclass of ItemDecoration from this gist: https://gist.github.com/alexfu/0f464fc3742f134ccd1e

How to make it only decorate items with certain condition? For instance, only decorate items with certain positions, type of ViewHolder, etc.

I have modified the above mentioned gist (plus some changes on deprecated Android API) with this code, but all items get decorated anyway:

public boolean isDecorated(View view, RecyclerView parent) {
    RecyclerView.ViewHolder holder = parent.getChildViewHolder(view);
    return holder instanceof MenuIconViewHolder || holder instanceof MenuDetailViewHolder;
}

@Override
public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
    if (isDecorated(view, parent)) {
        if (mOrientation == VERTICAL_LIST) {
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        } else {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        }
    } else {
        super.getItemOffsets(outRect, view, parent, state);
    }
}

What's wrong with above code? By the way, can it be considered best practice (in respect of separation of concerns) to place that kind of code in ItemDecoration class?

Answer 1

You need to call isDecorated on the draw method as well, because at the moment you don't put the offset on those items but you still draw over it.

The method loops over all the child views currently in the RecyclerView visible on the screen.

public void drawVertical(Canvas c, RecyclerView parent) {
    final int left = parent.getPaddingLeft();
    final int right = parent.getWidth() - parent.getPaddingRight();

    final int childCount = parent.getChildCount();
    for (int i = 0; i < childCount; i++) {
        final View child = parent.getChildAt(i);
        if(isDecorated(child, parent))
        {
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                .getLayoutParams();
            final int top = child.getBottom() + params.bottomMargin;
            final int bottom = top + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }
}

public void drawHorizontal(Canvas c, RecyclerView parent) {
    final int top = parent.getPaddingTop();
    final int bottom = parent.getHeight() - parent.getPaddingBottom();

    final int childCount = parent.getChildCount();
    for (int i = 0; i < childCount; i++) {
        final View child = parent.getChildAt(i);
        if(isDecorated(child, parent))
        {
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child
                .getLayoutParams();
            final int left = child.getRight() + params.rightMargin;
            final int right = left + mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(c);
        }
    }
}