Android开发在RecyclerView上面实现"拖放"和"滑动删除"-2

public interface OnStartDragListener {
 /**
 * Called when a view is requesting a start of a drag.
 *
 * @param viewHolder The holder of the view to drag.
 */
 void onStartDrag(RecyclerView.ViewHolder viewHolder);
}

public final ImageView handleView;
public ItemViewHolder(View itemView) {
 super(itemView);
 // ...
 handleView = (ImageView) itemView.findViewById(R.id.handle);
}

private final OnStartDragListener mDragStartListener;
public RecyclerListAdapter(OnStartDragListener dragStartListener) {
 mDragStartListener = dragStartListener;
 // ...
}
@Override
public void onBindViewHolder(final ItemViewHolder holder, 
 int position) {
 // ...
 holder.handleView.setOnTouchListener(new OnTouchListener() {
 @Override
 public boolean onTouch(View v, MotionEvent event) {
 if (MotionEventCompat.getActionMasked(event) == 
  MotionEvent.ACTION_DOWN) {
 mDragStartListener.onStartDrag(holder);
 }
 return false;
 }
 });
}

public class RecyclerListFragment extends Fragment implements 
 OnStartDragListener {
 // ...
 @Override
 public void onViewCreated(View view, Bundle icicle) {
 super.onViewCreated(view, icicle);
 RecyclerListAdapter a = new RecyclerListAdapter(this);
 // ...
 }
 @Override
 public void onStartDrag(RecyclerView.ViewHolder viewHolder) {
 mItemTouchHelper.startDrag(viewHolder);
 }
}

/**
 * Notifies a View Holder of relevant callbacks from 
 * {@link ItemTouchHelper.Callback}.
 */
public interface ItemTouchHelperViewHolder {
 /**
 * Called when the {@link ItemTouchHelper} first registers an 
 * item as being moved or swiped.
 * Implementations should update the item view to indicate 
 * it's active state.
 */
 void onItemSelected();
 /**
 * Called when the {@link ItemTouchHelper} has completed the 
 * move or swipe, and the active item state should be cleared.
 */
 void onItemClear();
}

@Override
public void onSelectedChanged(RecyclerView.ViewHolder viewHolder, 
 int actionState) {
 // We only want the active item
 if (actionState != ItemTouchHelper.ACTION_STATE_IDLE) {
 if (viewHolder instanceof ItemTouchHelperViewHolder) {
 ItemTouchHelperViewHolder itemViewHolder = 
  (ItemTouchHelperViewHolder) viewHolder;
 itemViewHolder.onItemSelected();
 }
 }
 super.onSelectedChanged(viewHolder, actionState);
}
@Override
public void clearView(RecyclerView recyclerView, 
 RecyclerView.ViewHolder viewHolder) {
 super.clearView(recyclerView, viewHolder);

 if (viewHolder instanceof ItemTouchHelperViewHolder) {
 ItemTouchHelperViewHolder itemViewHolder = 
 (ItemTouchHelperViewHolder) viewHolder;
 itemViewHolder.onItemClear();
 }
}

public class ItemViewHolder extends RecyclerView.ViewHolder 
 implements ItemTouchHelperViewHolder {
 // ...
 @Override
 public void onItemSelected() {
 itemView.setBackgroundColor(Color.LTGRAY);
 }
 @Override
 public void onItemClear() {
 itemView.setBackgroundColor(0);
 }
}

@Override
public int getMovementFlags(RecyclerView recyclerView, 
 RecyclerView.ViewHolder viewHolder) {
 int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN;
 int swipeFlags = ItemTouchHelper.START | ItemTouchHelper.END;
 return makeMovementFlags(dragFlags, swipeFlags);
}

int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | 
 ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;

@Override
public int getMovementFlags(RecyclerView recyclerView, 
 RecyclerView.ViewHolder viewHolder) {
 int dragFlags = ItemTouchHelper.UP | ItemTouchHelper.DOWN | 
  ItemTouchHelper.LEFT | ItemTouchHelper.RIGHT;
 int swipeFlags = 0;
 return makeMovementFlags(dragFlags, swipeFlags);
}

@Override
public void onChildDraw(Canvas c, RecyclerView recyclerView, 
 ViewHolder viewHolder, float dX, float dY, 
 int actionState, boolean isCurrentlyActive) {
 if (actiOnState== ItemTouchHelper.ACTION_STATE_SWIPE) {
 float width = (float) viewHolder.itemView.getWidth();
 float alpha = 1.0f - Math.abs(dX) / width;
 viewHolder.itemView.setAlpha(alpha);
 viewHolder.itemView.setTranslationX(dX); 
 } else {
 super.onChildDraw(c, recyclerView, viewHolder, dX, dY, 
  actionState, isCurrentlyActive);
 }
}