RecyclerView with alphabetical index

Question

I am trying to create a RecyclerView list with the alphabetical index on the right. I have a list that displays perfectly and is scrollable.

I am wondering if anyone can give me guidance in creating an alphabetical indexer. I believe that I need to iterate over the list and determine the letters used (I can do this). Then create a list of letters (for the indexer), and then use scrollToPosition (int position) to move to the desired item in the list when the letter is selected.

The main problem that I can’t deal with is not creating another list, but rather the relationship between the two lists. Any help would be greatly appreciated.

Answer 1

I believe this is the information you were looking for since I have

You can check out these libraries here:

danoz73 / RecyclerViewFastScroller

as far as I remember, he is the one who actually made the first index in recyclerview. I never did this in my application because there were a lot of problems setting it up.

AndroidDeveloperLB / LollipopContactsRecyclerViewFastScroller

readme said he had a lot of optimizations, so I think this is the best I could use, but I did not work it in my application.

code-computerlove / FastScrollRecyclerView

I think this is the design that you want correctly? Therefore, any of these libraries that you have used should suit your needs.

hope this helps

Answer 2

- FastScrollRecyclerView, Xamarin, ( xml .. .. - . , ).

, , ScrollToPosition ( ), Java Handler async Task.Delay. , . , . , - :)

public interface IFastScrollRecyclerViewAdapter
{
    Dictionary<string, int> GetMapIndex();
}

//

public class FastScrollRecyclerView : RecyclerView
{
    public const int INDWIDTH = 25;
    public const int INDHEIGHT = 18;
    public float ScaledWidth { get; set; }
    public float ScaledHeight { get; set; }
    public string[] Sections { get; set; }
    public float Sx { get; set; }
    public float Sy { get; set; }
    public string Section { get; set; }
    public bool ShowLetter { get; set; }

    private ListHandler _listHandler;
    private bool _setupThings = false;
    private Context _context;

    public FastScrollRecyclerView(Context context) : base(context)
    {
        _context = context;
    }

    public FastScrollRecyclerView(Context context, IAttributeSet attrs) : base(context, attrs)
    {
        _context = context;
    }

    public FastScrollRecyclerView(Context context, IAttributeSet attrs, int defStyle) : base(context, attrs, defStyle)
    {
        _context = context;
    }

    public override void OnDraw(Canvas c)
    {
        if (!_setupThings && GetAdapter() != null)
            SetupThings();
        base.OnDraw(c);
    }

    private void SetupThings()
    {
        //create az text data
        var sectionSet = ((IFastScrollRecyclerViewAdapter)GetAdapter()).GetMapIndex().Keys;
        var listSection = new List<string>(sectionSet);
        listSection.Sort();
        Sections = new string[listSection.Count];
        int i = 0;
        foreach (var s in listSection)
        {
            Sections[i++] = s;
        }

        ScaledWidth = INDWIDTH * _context.Resources.DisplayMetrics.Density;
        var divisor = sectionSet.Count == 0 ? 1 : sectionSet.Count;
        ScaledHeight = Height / divisor ;// INDHEIGHT * _context.Resources.DisplayMetrics.Density;
        Sx = Width - PaddingRight - (float)(1.2 * ScaledWidth);
        Sy = (float)((Height - (ScaledHeight * Sections.Length)) / 2.0);
        _setupThings = true;
    }

    public override bool OnTouchEvent(MotionEvent motionEvent)
    {
        if (_setupThings)
        {
            var adapter = GetAdapter() as IFastScrollRecyclerViewAdapter;

            var x = motionEvent.GetX();
            var y = motionEvent.GetY();

            switch (motionEvent.Action)
            {
                case MotionEventActions.Down:
                    {
                        if (x < Sx - ScaledWidth || y < Sy || y > (Sy + ScaledHeight * Sections.Length))
                        {
                            return base.OnTouchEvent(motionEvent);
                        }
                        else
                        {
                            //// We touched the index bar
                            float yy = y - PaddingTop - PaddingBottom - Sy;
                            int currentPosition = (int)Math.Floor(yy / ScaledHeight);
                            if (currentPosition < 0) currentPosition = 0;
                            if (currentPosition >= Sections.Length) currentPosition = Sections.Length - 1;
                            Section = Sections[currentPosition];
                            ShowLetter = true;
                            int positionInData = 0;
                            if (adapter.GetMapIndex().ContainsKey(Section.ToUpper()))
                            {
                                positionInData = adapter.GetMapIndex()[Section.ToUpper()];
                            }

                            (GetLayoutManager() as LinearLayoutManager).ScrollToPositionWithOffset(positionInData, 20);
                            Invalidate();
                        }
                        break;
                    }
                case MotionEventActions.Move:
                    {
                        if (!ShowLetter && (x < Sx - ScaledWidth || y < Sy || y > (Sy + ScaledHeight * Sections.Length)))
                        {
                            return base.OnTouchEvent(motionEvent);
                        }
                        else
                        {
                            float yy = y - Sy;
                            int currentPosition = (int)Math.Floor(yy / ScaledHeight);
                            if (currentPosition < 0) currentPosition = 0;
                            if (currentPosition >= Sections.Length) currentPosition = Sections.Length - 1;
                            Section = Sections[currentPosition];
                            ShowLetter = true;
                            int positionInData = 0;
                            if (adapter.GetMapIndex().ContainsKey(Section.ToUpper()))
                                positionInData = adapter.GetMapIndex()[Section.ToUpper()];
                            (GetLayoutManager() as LinearLayoutManager).ScrollToPositionWithOffset(positionInData, 20);
                            Invalidate();
                        }
                        break;
                    }
                case MotionEventActions.Up:
                    {
                        _listHandler = new ListHandler(this);
                        _listHandler.DelayClear();
                        if (x < Sx - ScaledWidth || y < Sy || y > (Sy + ScaledHeight * Sections.Length))
                        {
                            return base.OnTouchEvent(motionEvent);
                        }
                        else
                        {
                            return true;
                        }
                    }
            }
        }

        return true;
    }

    private class ListHandler
    {
        FastScrollRecyclerView _parent;
        public ListHandler (FastScrollRecyclerView parent)
        {
            _parent = parent;
        }

        public async void DelayClear()
        {
            await Task.Delay(100);
            _parent.ShowLetter = false;
            _parent.Invalidate();
        }
    }
}

//

public class FastScrollRecyclerViewItemDecoration : ItemDecoration
    {
        private Context _context;
        public FastScrollRecyclerViewItemDecoration(Context context)
        {
            _context = context;
        }

        public override void OnDrawOver(Canvas canvas, RecyclerView parent, State state)
        {
            base.OnDrawOver(canvas, parent, state);

            float scaledWidth = ((FastScrollRecyclerView)parent).ScaledWidth;
            float sx = ((FastScrollRecyclerView)parent).Sx;
            float scaledHeight = ((FastScrollRecyclerView)parent).ScaledHeight;
            float sy = ((FastScrollRecyclerView)parent).Sy;
            string[] sections = ((FastScrollRecyclerView)parent).Sections;
            string section = ((FastScrollRecyclerView)parent).Section;
            bool showLetter = ((FastScrollRecyclerView)parent).ShowLetter;

            // We draw the letter in the middle
            if (showLetter & section != null && !section.Equals(""))
            {
                //overlay everything when displaying selected index Letter in the middle
                Paint overlayDark = new Paint();
                overlayDark.Color = Color.Black;
                overlayDark.Alpha = 100;
                canvas.DrawRect(0, 0, parent.Width, parent.Height, overlayDark);
                float middleTextSize = _context.Resources.GetDimension(Resource.Dimension.fast_scroll_overlay_text_size );
                Paint middleLetter = new Paint();
                middleLetter.Color = new Color(ContextCompat.GetColor(_context, Resource.Color.primary));
                middleLetter.TextSize = middleTextSize;
                middleLetter.AntiAlias = true;
                middleLetter.FakeBoldText = true;
                middleLetter.SetStyle(Paint.Style.Fill);
                int xPos = (canvas.Width - (int)middleTextSize) / 2;
                int yPos = (int)((canvas.Height / 2) - ((middleLetter.Descent() + middleLetter.Ascent()) / 2));


                canvas.DrawText(section.ToUpper(), xPos, yPos, middleLetter);
            }

            //        // draw indez A-Z

            Paint textPaint = new Paint();
            textPaint.AntiAlias = true;
            textPaint.SetStyle(Paint.Style.Fill);

            for (int i = 0; i < sections.Length; i++)
            {
                if (showLetter & section != null && !section.Equals("") && section != null
                        && sections[i].ToUpper().Equals(section.ToUpper()))
                {
                    textPaint.Color = Color.White;
                    textPaint.Alpha = 255;
                    textPaint.FakeBoldText = true;
                    textPaint.TextSize = scaledWidth / 2;
                    canvas.DrawText(sections[i].ToUpper(),
                            sx + textPaint.TextSize / 2, sy + parent.PaddingTop
                                    + scaledHeight * (i + 1), textPaint);
                    textPaint.TextSize = scaledWidth;
                    canvas.DrawText("•",
                            sx - textPaint.TextSize / 3, sy + parent.PaddingTop
                                    + scaledHeight * (i + 1) + scaledHeight / 3, textPaint);

                }
                else
                {
                    textPaint.Color = new Color(ContextCompat.GetColor(_context, Resource.Color.primary));
                    textPaint.Alpha = 200;
                    textPaint.FakeBoldText = false;
                    textPaint.TextSize = scaledWidth / 2;
                    canvas.DrawText(sections[i].ToUpper(),
                            sx + textPaint.TextSize / 2, sy + parent.PaddingTop
                                    + scaledHeight * (i + 1), textPaint);
                }
            }
        }
    }