RecyclerView与字母索引

Question

我正在尝试构建一个RecyclerView列表，右侧有一个按字母顺序排列的索引器。我有完美的列表显示并且能够滚动。

我想知道是否有人可以在构建字母索引器方面给我一些指导。我相信我需要遍历我的列表并确定使用的字母（我可以这样做）。然后构建字母列表（对于索引器），然后使用scrollToPosition（int position）在选择字母时移动到列表中的右项。

我无法解决的主要问题是没有建立另一个列表，而是两个列表之间的通信。任何帮助将不胜感激。

Answer 1

我相信这是你一直在寻找的信息

您可以在此处查看这些库：

danoz73/RecyclerViewFastScroller

据我记得，他是在recyclerview中实际制作第一个字母索引器的人。我从未在我的应用程序中使用它，因为定制它有很多问题。

AndroidDeveloperLB/LollipopContactsRecyclerViewFastScroller

自述文件说他已经做了很多优化，所以我认为这是我能用的最好的，但我现在还没有在我的应用程序中使用它。

code-computerlove/FastScrollRecyclerView

我认为这是你想要的设计吗？因此，您使用它们中的任何一个都应该满足您的需求。

希望有所帮助

Answer 2

如果有人想在Xamarin中使用上面提到的FastScrollRecyclerView ，我只需移植主要类（您仍然需要创建xml资源并准备索引等等 - 请参阅原始回购指南，很简单）。

我在问题页面中提出了调整以改进ScrollToPosition和索引高度（这也使它在横向上工作），并且还为异步Task.Delay切换了Java Handler类。它可能仍有问题，否则它是一个直接的端口。似乎没问题。希望我已经节省了一些时间：）

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);
                }
            }
        }
    }