在小吃店上调用UNDO按钮时，已删除的项目为空

Question

I'm trying to implement the feature "Swipe to delete" item in recycleview. But the deleted item is can not restore correctly when invoke UNDO action on snackbar.

This is error. https://i.imgur.com/hPfaBQX.png

I have tried to implement onChildDraw in different ways, but it does not work

@Override
public void onSwiped(RecyclerView.ViewHolder viewHolder, int direction, int position) {

// backup of removed item
final String deletedItem = adapter.arrIgnoreNumber.get(viewHolder.getAdapterPosition());
final int deletedIndex = viewHolder.getAdapterPosition();


adapter.removeItem(viewHolder.getAdapterPosition());
// showing snack bar with Undo option
Snackbar snackbar = Snackbar.make(coordinatorLayout, "Removed from the list!", Snackbar.LENGTH_LONG);
snackbar.setAction("UNDO", new View.OnClickListener() {
                        @Override
                        public void onClick(View view) {
                            adapter.restoreItem(deletedItem, deletedIndex);
                        }
                    });
                    snackbar.setActionTextColor(Color.YELLOW);
                    snackbar.show();
                }
}

@Override
public void onChildDraw(@NonNull Canvas c, @NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
Bitmap icon;
            Paint p = new Paint();
            if(actionState == ItemTouchHelper.ACTION_STATE_SWIPE){

                View itemView = viewHolder.itemView;
                float height = (float) itemView.getBottom() - (float) itemView.getTop();
                float width = height / 3;

                if(dX > 0){
                    p.setColor(Color.parseColor("#388E3C"));
                    RectF background = new RectF((float) itemView.getLeft(), (float) itemView.getTop(), dX,(float) itemView.getBottom());
                    c.drawRect(background,p);
                    icon = BitmapFactory.decodeResource(mContext.getResources(), R.drawable.ic_delete);
                    RectF icon_dest = new RectF((float) itemView.getLeft() + width ,(float) itemView.getTop() + width,(float) itemView.getLeft()+ 2*width,(float)itemView.getBottom() - width);
                    c.drawBitmap(icon,null,icon_dest,p);
                } else {
                    p.setColor(Color.parseColor("#D32F2F"));
                    RectF background = new RectF((float) itemView.getRight() + dX, (float) itemView.getTop(),(float) itemView.getRight(), (float) itemView.getBottom());
                    c.drawRect(background,p);
                    icon = BitmapFactory.decodeResource(mContext.getResources(), R.drawable.ic_delete);
                    RectF icon_dest = new RectF((float) itemView.getRight() - 2*width ,(float) itemView.getTop() + width,(float) itemView.getRight() - width,(float)itemView.getBottom() - width);
                    c.drawBitmap(icon,null,icon_dest,p);
                }
            }
            super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
        }

I expect the deleted item can restore in list

• Update: I provide my adapter for more detail:

@NonNull
        @Override
        public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int i) {
            LayoutInflater inflater = LayoutInflater.from(parent.getContext());
            View view = inflater.inflate(R.layout.list_ignore_item, parent, false);
            return new ViewHolder(view);
        }

@Override
        public void onBindViewHolder(@NonNull ViewHolder viewHolder, int position) {
            final int tmpPos = position;
            viewHolder.phone.setText(arrIgnoreNumber.get(position));
            String name = arrIgnoreNumber.get(position);
            if (!name.isEmpty()) {
                viewHolder.phone.setVisibility(View.VISIBLE);
                viewHolder.name.setText(name);
            } else {
                viewHolder.phone.setVisibility(View.GONE);
                viewHolder.name.setText(arrIgnoreNumber.get(position));
            }
            viewHolder.icon.setImageBitmap(Utils.getBitmapByContactNumber(mContext, arrIgnoreNumber.get(position), false));

@Override
        public long getItemId(int position) {
            return position;
        }

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

        public void removeItem(int position) {
            arrIgnoreNumber.remove(position);
            notifyItemRemoved(position);
        }

        public void restoreItem(String item, int position) {
            arrIgnoreNumber.add(position, item);
            notifyItemInserted(position);
        }

Answer 1

The following solution works for me. Refer to https://www.androidhive.info/2017/09/android-recyclerview-swipe-delete-undo-using-itemtouchhelper/

1. In ItemTouchHelper.SimpleCallback :

@Override
        public int getMovementFlags(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder) {
            return makeMovementFlags(0, ItemTouchHelper.LEFT);
        }

        @Override
        public boolean onMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target) {
            return false;
        }

        @Override
        public void onSwiped(@NonNull RecyclerView.ViewHolder viewHolder, int direction) {
            listener.onSwiped(viewHolder, direction, viewHolder.getAdapterPosition());
        }

        @Override
        public void onSelectedChanged(@Nullable RecyclerView.ViewHolder viewHolder, int actionState) {
            if (viewHolder != null) {
                final View foregroundView = ((IgnoreCallAdapter.ViewHolder) viewHolder).foreground;
                getDefaultUIUtil().onSelected(foregroundView);
            }
        }

        @Override
        public void onChildDrawOver(@NonNull Canvas c, @NonNull RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
            final View foregroundView = ((IgnoreCallAdapter.ViewHolder) viewHolder).foreground;
            getDefaultUIUtil().onDrawOver(c, recyclerView, foregroundView, dX, dY,
                    actionState, isCurrentlyActive);
        }

        @Override
        public void onChildDraw(@NonNull Canvas c, @NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, boolean isCurrentlyActive) {
            final View foregroundView = ((IgnoreCallAdapter.ViewHolder) viewHolder).foreground;
            getDefaultUIUtil().onDraw(c, recyclerView, foregroundView, dX, dY,
                    actionState, isCurrentlyActive);
        }

        @Override
        public void clearView(@NonNull RecyclerView recyclerView, @NonNull RecyclerView.ViewHolder viewHolder) {
            final View foregroundView = ((IgnoreCallAdapter.ViewHolder) viewHolder).foreground;
            getDefaultUIUtil().clearView(foregroundView);
        }

        @Override
        public float getSwipeThreshold(@NonNull RecyclerView.ViewHolder viewHolder) {
            return 0.7f;
        }

        @Override
        public int convertToAbsoluteDirection(int flags, int layoutDirection) {
            return super.convertToAbsoluteDirection(flags, layoutDirection);
        }

2. In item layout xml :

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="@dimen/row_view_height_ignore_list"
    android:focusable="true"
    android:foreground="?android:attr/selectableItemBackground"
    android:orientation="vertical">

    <RelativeLayout
        android:id="@+id/ignore_item_background"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/ignore_item_bg">
    </RelativeLayout>


    <LinearLayout
        android:id="@+id/ignore_item_foreground"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@drawable/bg_ignore_item_foreground"
        android:orientation="horizontal"
        android:visibility="visible">
        </LinearLayout>

    </LinearLayout>

</FrameLayout>