Xamarin Android: How to swipe left recyclerview items

Question

Hello everyone my name is Taniguchi:

I have a recyclerview and i wish to swipe to Delete in xamarin android but i only find articles in java

does anyone knows how to do it in C# ?

The java article teaching how to swipe to delete.

https://medium.com/@zackcosborn/step-by-step-recyclerview-swipe-to-delete-and-undo-7bbae1fce27e

my recylerview adapter:

public class RecyclerAdapter : RecyclerView.Adapter, View.IOnClickListener, View.IOnLongClickListener
{
    private View view;
    private Boolean isSelected = false;

    public Boolean IsSelected()
    {
        return isSelected;
    }

    public void setSelected(Boolean selected)
    {

        isSelected = selected;
    }

    public static RecyclerView.Adapter mAdapter;
    public static bool isActionMode = true;
    private int viewType;
    private ViewGroup parent;
    public static bool unselect = false;
    private Activity mActivity;
    private MyActionMode mActionMode;
    private RecyclerView.ViewHolder holder;
    private List<time_entry> mTime_Entries;
    private Context context;
    private View p;
    private ActionMode mode;
    public static bool count = false;
    public static int CountAuxiliar = 0;
    private MyActionMode myActionMode;

    public event EventHandler<int> ItemClick;
    public RecyclerAdapter(List<time_entry> time_entries, Context context)
    {
        mTime_Entries = time_entries;
        this.context = context;
    }

    public RecyclerAdapter(List<time_entry> time_entries, Activity activity)
    {
        mTime_Entries = time_entries;
        mActivity = activity;
    }

    public RecyclerAdapter(List<time_entry> time_entries, MyActionMode myActionMode)
    {
        mTime_Entries = time_entries;
        this.myActionMode = myActionMode;
    }

    public class MyView : RecyclerView.ViewHolder
    {
        public View mMainView {get; set;}
        public TextView mName {get; set;}
        public TextView mSubject {get; set;}
        public TextView mMessage {get; set;}

        public MyView(View view) : base(view)
        {
            mMainView = view;
        }

    }


    public  override int ItemCount
    {
        get { return mTime_Entries.Count; }
    }

    public  override RecyclerView.ViewHolder OnCreateViewHolder(ViewGroup parent, int viewType)
    {
        LayoutInflater inflater = LayoutInflater.From(parent.Context);
        View row = LayoutInflater.From(parent.Context).Inflate(Resource.Layout.row, parent, false);
        RecyclerViewHolder vh = new RecyclerViewHolder(row);
        return vh;
    }

    public  override void OnBindViewHolder(RecyclerView.ViewHolder holder, int position)
    {

        RecyclerViewHolder myHolder = holder as RecyclerViewHolder;
        myHolder.cbx.Visibility = mTime_Entries[position].IsSelected() ? ViewStates.Visible : ViewStates.Gone;
        myHolder.cbx.Checked = mTime_Entries[position].IsSelected();


        myHolder.mProject_Task.Text = mTime_Entries[position].projectTask;
        myHolder.mDate.Text = mTime_Entries[position].date;
        myHolder.mDescription.Text = mTime_Entries[position].description;


        myHolder.ItemView.SetBackgroundColor(mTime_Entries[position].IsSelected() ? Color.LightBlue : Color.Transparent);
        myHolder.ItemView.Tag = position;
        myHolder.ItemView.SetOnClickListener(this);
        myHolder.ItemView.SetOnLongClickListener(this);

    }

    void View.IOnClickListener.OnClick(View v)
    {
        if (CountAuxiliar > 0)
        {
            int position = (int)v.Tag;
            mTime_Entries[position].setSelected(!mTime_Entries[position].IsSelected());
            v.SetBackgroundColor(mTime_Entries[position].IsSelected() ? Color.LightBlue : Color.Transparent);
            v.FindViewById(Resource.Id.checkBox1).Visibility = mTime_Entries[position].IsSelected() ? ViewStates.Visible : ViewStates.Invisible;
            if (mTime_Entries[position].IsSelected())
            {
                CountAuxiliar++;
            }
            else
            {
                CountAuxiliar--;
            }
            //mode.Title = CountAuxiliar.ToString() + " " + "Selecionados";
            MainActivity.title.Text = CountAuxiliar.ToString() + " " + "Selecionados";
            Toast.MakeText(v.Context, "Click : " + CountAuxiliar + "---" + position, ToastLength.Short).Show();
        }
        if (CountAuxiliar < 1 && count == true)
        {
            count = false;
            MainActivity.toolbar2.Visibility = ViewStates.Gone;
            MainActivity.bottomnavigationview1.Visibility = ViewStates.Gone;
            MainActivity.floatinactionbutton1.Visibility = ViewStates.Visible;
        }
    }
    public void removeSelection()
    {
        if (mTime_Entries != null)
        {
            foreach (time_entry email in mTime_Entries)
            {
                email.setSelected(false);

            }
        }
       NotifyDataSetChanged();
        CountAuxiliar = 0;
        count = false;
        MainActivity.bottomnavigationview1.Visibility = ViewStates.Gone;
        MainActivity.floatinactionbutton1.Visibility = ViewStates.Visible;

    }

    public void checkall()
    {
        if (mTime_Entries != null)
        {
            foreach (time_entry email in mTime_Entries)
            {
                email.setSelected(true);

            }
        }
        NotifyDataSetChanged();
        MainActivity.bottomnavigationview1.Visibility = ViewStates.Visible;
    }


    public bool OnLongClick(View v)
    {

        if (CountAuxiliar < 1)
        {
            CountAuxiliar = 1;
            count = true;
            int position = (int)v.Tag;
            mTime_Entries[position].setSelected(!mTime_Entries[position].IsSelected());
            v.SetBackgroundColor(mTime_Entries[position].IsSelected() ? Color.LightBlue : Color.Transparent);
            MainActivity.bottomnavigationview1.Visibility = ViewStates.Visible;
            MainActivity.floatinactionbutton1.Visibility = ViewStates.Gone;
            v.FindViewById(Resource.Id.checkBox1).Visibility = mTime_Entries[position].IsSelected() ? ViewStates.Visible : ViewStates.Invisible;
            MainActivity.title.Text = CountAuxiliar.ToString() + " " + "Selecionado";

            MainActivity.toolbar2.Visibility = ViewStates.Visible;
            count = true;

            Toast.MakeText(v.Context, "Long Click : " + mTime_Entries[position].IsSelected() + "---" + position, ToastLength.Short).Show();
        }
        return true;
    }
}

Answer 1

You can custom a SwipeToDeleteCallback inherited from ItemTouchHelper.SimpleCallback to realize it , here is an article for reference .

SwipeToDeleteCallback class:

public class SwipeToDeleteCallback : ItemTouchHelper.SimpleCallback
{
    private Context context;
    private PhotoAlbumAdapter madapter;
    private Android.Graphics.Drawables.Drawable deleteIcon;
    private int intrinsicWidth;
    private int intrinsicHeight;
    private Android.Graphics.Drawables.ColorDrawable background;
    private Color backgroundColor;
    private Paint clearPaint;

    public SwipeToDeleteCallback(int dragDirs, int swipeDirs, Context context) : base(dragDirs, swipeDirs )
    {
        this.context = context;
        deleteIcon = ContextCompat.GetDrawable(context, Resource.Drawable.alter_delete);
        intrinsicWidth = deleteIcon.IntrinsicWidth;
        intrinsicHeight = deleteIcon.IntrinsicHeight;
        background = new Android.Graphics.Drawables.ColorDrawable();
        backgroundColor = Color.ParseColor("#f44336");
        clearPaint = new Paint();
        clearPaint.SetXfermode(new PorterDuffXfermode(PorterDuff.Mode.Clear));
    }

    public SwipeToDeleteCallback(int dragDirs, int swipeDirs, Context context, PhotoAlbumAdapter mRecyclerView) : this(dragDirs, swipeDirs, context)
    {
        this.context = context;
        this.madapter = mRecyclerView;
        deleteIcon = ContextCompat.GetDrawable(context, Resource.Drawable.delete);
        intrinsicWidth = deleteIcon.IntrinsicWidth;
        intrinsicHeight = deleteIcon.IntrinsicHeight;
        background = new Android.Graphics.Drawables.ColorDrawable();
        backgroundColor = Color.ParseColor("#f44336");
        clearPaint = new Paint();
        clearPaint.SetXfermode(new PorterDuffXfermode(PorterDuff.Mode.Clear));
    }

    public override int GetMovementFlags(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder)
    {
        if(viewHolder.AdapterPosition == 10)
        {
            return 0;
        }
        return base.GetMovementFlags(recyclerView, viewHolder);
    }

    public override void OnChildDraw(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, bool isCurrentlyActive)
    {
        base.OnChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
    }

    public override bool OnMove(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, RecyclerView.ViewHolder target)
    {
        //throw new NotImplementedException();
        return false;
    }

    public override void OnChildDrawOver(Canvas c, RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder, float dX, float dY, int actionState, bool isCurrentlyActive)
    {
        var itemView = viewHolder.ItemView;
        var itemHeight = itemView.Bottom - itemView.Top;
        var isCanceled = dX == 0f && !isCurrentlyActive;

        if (isCanceled)
        {
            clearCanvas(c, itemView.Right + dX, (float)itemView.Top, (float)itemView.Right, (float)itemView.Bottom);
            base.OnChildDrawOver(c, recyclerView
                , viewHolder, dX, dY, actionState, isCurrentlyActive);
            return;
        }
        background.Color = backgroundColor;
        background.SetBounds(itemView.Right + (int)dX, itemView.Top, itemView.Right, itemView.Bottom);
        background.Draw(c);

        var deleteIconTop = itemView.Top + (itemHeight - intrinsicHeight) / 2;
        var deleteIconMargin = (itemHeight - intrinsicHeight) / 2;
        var deleteIconLeft = itemView.Right - deleteIconMargin - intrinsicWidth;
        var deleteIconRight = itemView.Right - deleteIconMargin;
        var deleteIconBottom = deleteIconTop + intrinsicHeight;

        deleteIcon.SetBounds(deleteIconLeft, deleteIconTop, deleteIconRight, deleteIconBottom);
        deleteIcon.Draw(c);

        base.OnChildDrawOver(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive);
    }

    private void clearCanvas(Canvas c, float v, float top, float right, float bottom)
    {
        c.DrawRect(v, top, right, bottom, clearPaint);
    }

    public override void OnSwiped(RecyclerView.ViewHolder viewHolder, int direction)
    {
        //Invoke Removing Item method from adapter
        this.madapter.RemoveItem(viewHolder.AdapterPosition);
    }

    public override void ClearView(RecyclerView recyclerView, RecyclerView.ViewHolder viewHolder)
    {
        base.ClearView(recyclerView, viewHolder);
    }
}

Then in Activity can use it as follow:

 var swipeHandler = new SwipeToDeleteCallback(0, ItemTouchHelper.Left, this, mAdapter);
 var itemTouchHelper = new ItemTouchHelper(swipeHandler);
 itemTouchHelper.AttachToRecyclerView(mRecyclerView);

Not forgetting to add Remove method in Adapter :

public void RemoveItem (int position)
{
    ArrayList al = new ArrayList(mPhotoAlbum.mPhotos);
    al.RemoveAt(position);
    mPhotoAlbum.mPhotos = (Photo[])al.ToArray(typeof(Photo));
    NotifyDataSetChanged();
    NotifyItemChanged(position);
}

Maybe from code not understanding totally , I refer to this sample to realize it . And the modified sample will share here . The effect is as follow:

===================================Update====================================

From shared project , there are two places need to modify.

First is RemoveItem method in RecyclerAdapter class.Because my project use Object[] to set source for RecycleView , need to write code to convert to be a ArrayList .However ,the source (mTime_Entries) of your project is also a List[] , so not need to convert it. Modify as follow in your project:

public void RemoveItem(int position)
{
    mTime_Entries.RemoveAt(position);
    NotifyDataSetChanged();
    NotifyItemChanged(position);
}

Second is OnSwiped method in SwipeToDeleteCallback class.Before this , you also need to modify the constructor of SwipeToDeleteCallback. The Adapter is not correct here.

  private RecyclerAdapter mdapter;

  public SwipeToDeleteCallback(int dragDirs, int swipeDirs, Context context, PhotoAlbumAdapter mRecyclerView) : this(dragDirs, swipeDirs, context)
{
    this.context = context;
    this.madapter = mRecyclerView;
    deleteIcon = ContextCompat.GetDrawable(context, Resource.Drawable.delete);
    intrinsicWidth = deleteIcon.IntrinsicWidth;
    intrinsicHeight = deleteIcon.IntrinsicHeight;
    background = new Android.Graphics.Drawables.ColorDrawable();
    backgroundColor = Color.ParseColor("#f44336");
    clearPaint = new Paint();
    clearPaint.SetXfermode(new PorterDuffXfermode(PorterDuff.Mode.Clear));
}

You should keep them(Adapter) be the same between MainActity and here.

Then OnSwiped can be written with one line code as follow:

public override void OnSwiped(RecyclerView.ViewHolder viewHolder, int direction)
{
    //Invoke Removing Item method from 
    this.mdapter.RemoveItem(viewHolder.AdapterPosition);
}