Hello Friends,

This tutorial will help you to implement "drag & drop" and "swipe" functionality  with Recyclerview items. There are many different ways to implement this features but we are using really a simple way to add these features in Recyclerview. It’s already part of the Android Support Library and needs one class. This class is called ItemTouchHelper.

ItemTouchHelper :- ItemTouchHelper is a powerful class that can do everything you need to drag, drop, swipe in RecyclerView. It’s a subclass of RecyclerView.ItemDecoration, that mean it's easily added to existing LinearLayout Manager and Adapter.

We can implement this feature by following steps.

Step-1: First we’ll create an interface ItemTouchHelperAdapter that allows us to pass two events onMove() and onSwiped() event callbacks back up the chain.

public interface ItemTouchHelperAdapter { 

 void onItemMove(int fromPosition, int toPosition);
 void onItemDismiss(int position);
 
}

This interface will implement by RecyclerViewAdapter class as listener

Step-2: Defined here complete code for RecyclerView Adapter which implement ItemTouchHelperAdapter interface

public class RecylerViewAdapter extends RecyclerView.Adapter<RecylerViewAdapter.ViewHolder>  implements ItemTouchHelperAdapter {


    private ArrayList<String> list;
    private final OnStartDragListener mDragStartListener;


    public RecylerViewAdapter(ArrayList<String> list, Context context, OnStartDragListener dragStartListener) {

        this.list = list;
        mDragStartListener = dragStartListener;



    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_layout, parent, false);
        return new ViewHolder(v);
    }

    @Override
    public void onBindViewHolder(final ViewHolder holder, final int position) {

        holder.textView.setText(list.get(position));
        holder.imageView.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {

                if (MotionEventCompat.getActionMasked(event) == MotionEvent.ACTION_DOWN) {
                    mDragStartListener.onStartDrag(holder);
                }
                return false;
            }
        });





    }

    @Override
    public int getItemCount() {
        return list.size();
    }

    @Override
    public boolean onItemMove(int fromPosition, int toPosition) {

        Collections.swap(list, fromPosition, toPosition);
        notifyItemMoved(fromPosition, toPosition);
        return true;
    }

    @Override
    public void onItemDismiss(int position) {

        list.remove(position);
        notifyItemRemoved(position);

    }

    public class ViewHolder extends RecyclerView.ViewHolder implements
            ItemTouchHelperViewHolder {

        TextView textView;
        ImageView imageView;


        public ViewHolder(View itemView) {
            super(itemView);

            textView=(TextView)itemView.findViewById(R.id.text);
            imageView=(ImageView)itemView.findViewById(R.id.handle);



        }

        @Override
        public void onItemSelected() {

            itemView.setBackgroundColor(Color.LTGRAY);
        }

        @Override
        public void onItemClear() {

            itemView.setBackgroundColor(0);
        }
    }



}

Here it is very necessary to call notifyItemRemoved() and notifyItemMoved() so that Adapter will get aware when any changes happen.

Step-3: Defined another interface ItemTouchHelperViewHolder and implement by ViewHolder class.

This interface holds two callbacks events. This callback call when you selected any item from RecyclerView.

public interface ItemTouchHelperViewHolder {

 / * Implementations should update the item view to indicate it's active state. */ 
void onItemSelected(); 

/*
Called when completed the move or swipe, and the active item * state should be cleared. 
*/ 

void onItemClear();

 } 

Step-4: Defined interface OnStartDragListener .

**
 * Listener for manual initiation of a drag.
 */
public interface OnStartDragListener {

    /**
     * Called when a view is requesting a start of a drag.
     */
    void onStartDrag(RecyclerView.ViewHolder viewHolder);

}

Finally, We will define resulting call back class SimpleItemTouchHelperCallback

public class SimpleItemTouchHelperCallback extends ItemTouchHelper.Callback {

    public static final float ALPHA_FULL = 1.0f;

    private final ItemTouchHelperAdapter mAdapter;

    public SimpleItemTouchHelperCallback(ItemTouchHelperAdapter adapter) {
        mAdapter = adapter;
    }

    @Override
    public boolean isLongPressDragEnabled() {
        return true;
    }

    @Override
    public boolean isItemViewSwipeEnabled() {
        return true;
    }

    @Override
    public int getMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        // Set movement flags based on the layout manager
        if (recyclerView.getLayoutManager() instanceof GridLayoutManager) {
            final int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
            final int swipeFlags = 0;
            return makeMovementFlags(dragFlags, swipeFlags);
        } else {
            final int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
            final int swipeFlags = ItemTouchHelper.START | ItemTouchHelper.END;
            return makeMovementFlags(dragFlags, swipeFlags);
        }
    }

    @Override
    public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder source, RecyclerView.ViewHolder target) {
        if (source.getItemViewType() != target.getItemViewType()) {
            return false;
        }

        // Notify the adapter of the move
        mAdapter.onItemMove(source.getAdapterPosition(), target.getAdapterPosition());
        return true;
    }

    @Override
    public void onSwiped(RecyclerView.ViewHolder viewHolder, int i) {
        // Notify the adapter of the dismissal
        mAdapter.onItemDismiss(viewHolder.getAdapterPosition());
    }

    @Override
    public void onChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
        if (actionState == ItemTouchHelper.ACTION_STATE_SWIPE) {
            // Fade out the view as it is swiped out of the parent's bounds
            final float alpha = ALPHA_FULL - Math.abs(dX) / (float) viewHolder.itemView.getWidth();
            viewHolder.itemView.setAlpha(alpha);
            viewHolder.itemView.setTranslationX(dX);
        } else {
            super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
        }
    }

    @Override
    public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, int actionState) {
        // We only want the active item to change
        if (actionState != ItemTouchHelper.ACTION_STATE_IDLE) {
            if (viewHolder instanceof ItemTouchHelperViewHolder) {
                // Let the view holder know that this item is being moved or dragged
                ItemTouchHelperViewHolder itemViewHolder = (ItemTouchHelperViewHolder) viewHolder;
                itemViewHolder.onItemSelected();
            }
        }

        super.onSelectedChanged(viewHolder, actionState);
    }

    @Override
    public void clearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder) {
        super.clearView(recyclerView, viewHolder);

        viewHolder.itemView.setAlpha(ALPHA_FULL);

        if (viewHolder instanceof ItemTouchHelperViewHolder) {
            // Tell the view holder it's time to restore the idle state
            ItemTouchHelperViewHolder itemViewHolder = (ItemTouchHelperViewHolder) viewHolder;
            itemViewHolder.onItemClear();
        }
    }
}

Step-5 : With our Callback ready, we can create our ItemTouchHelper and call attachToRecyclerView(RecyclerView) in MainActivity class and implement interface onStartDragListener.

ItemTouchHelper.Callback callback = new SimpleItemTouchHelperCallback(adapter); 

ItemTouchHelper touchHelper = new ItemTouchHelper(callback); 

touchHelper.attachToRecyclerView(recyclerView);

@Override
public void onStartDrag(RecyclerView.ViewHolder viewHolder) {
  mItemTouchHelper.startDrag(viewHolder);
}

Step-6: Create a XML file for the items in RecyclerView item_layout.xml

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/item"
    android:layout_width="match_parent"
    android:layout_height="?listPreferredItemHeight"
    android:clickable="true"
    android:focusable="true"
    android:foreground="?selectableItemBackground">

    <TextView
        android:id="@+id/text"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_vertical"
        android:layout_marginLeft="@dimen/activity_horizontal_margin"
        android:textAppearance="?android:attr/textAppearanceMedium" />

    <ImageView
        android:id="@+id/handle"
        android:layout_width="?listPreferredItemHeight"
        android:layout_height="match_parent"
        android:layout_gravity="center_vertical|right"
        android:scaleType="center"
        android:src="@drawable/ic_reorder_grey_500_24dp" />
</FrameLayout>