Tools for RecyclerMergeAdapter

android-recycler-merge-adapter-tools

    /**
     * Calculates correct item position based on RecyclerAdapter and ViewHolder adapter position.
     * Takes in consideration RecyclerMergeAdapter and adjust position accordingly
     *
     * @param adapter    RecyclerAdapter with access to RecyclerView instance
     * @param viewHolder ViewHolder that was created by @adapter
     * @return adjusted local position for viewHolder
     */
    public static int getLocalPosition(RecyclerAdapter adapter, RecyclerView.ViewHolder viewHolder) {
        int position = viewHolder.getAdapterPosition();
        if (position == RecyclerView.NO_POSITION) {
            // ViewHolder is in transition, data is not available
            return RecyclerView.NO_POSITION;
        }

        final RecyclerView recyclerView = adapter.getRecyclerView();
        if (recyclerView == null) {
            // Adapter is not attached
            return RecyclerView.NO_POSITION;
        }

        final RecyclerView.Adapter mainAdapter = recyclerView.getAdapter();

        // Small optimization to avoid unnecessary calls for instanceOf
        if (adapter == mainAdapter) {
            return position;
        }

        if (mainAdapter instanceof RecyclerMergeAdapter) {
            final RecyclerMergeAdapter mergeAdapter = (RecyclerMergeAdapter) mainAdapter;
            position = mergeAdapter.getLocalPosition(position);

            if (position == RecyclerView.NO_POSITION) {
                // Something wrong with position
                return RecyclerView.NO_POSITION;
            }
        }

        return position;
    }
    
    
    /**
     * Calculates local adapter position from global position in MergeAdapter
     *
     * @param globalPosition - global position in merge adapter
     * @return position local for current adapter
     */
    public int getLocalPosition(int globalPosition) {
        int positionStart = 0;
        int positionEnd = 0;
        for (Adapter adapter : getActiveItems()) {
            positionEnd += positionStart + adapter.getItemCount();
            if (globalPosition >= positionStart && globalPosition < positionEnd) {
                return globalPosition - positionStart;
            } else {
                positionStart = positionEnd;
            }
        }

        return NO_POSITION;
    }