A Xamarin Android TextView that supports Linkify and gestures

LinkifyTextView.cs

// -----------------------------------------------------------------------
// <copyright file="LinkifyTextView.cs" company="Conglomo">
// Copyright 2019 Peter Chapman. All rights reserved.
// </copyright>
// -----------------------------------------------------------------------

namespace Conglomo.AndroidSupport
{
    using Android.Content;
    using Android.Runtime;
    using Android.Text;
    using Android.Text.Style;
    using Android.Text.Util;
    using Android.Util;
    using Android.Views;
    using Android.Widget;
    using Java.Lang;

    /// <summary>
    /// A TextView that supports linkifying of hyperlinks and gestures.
    /// </summary>
    /// <seealso cref="Android.Widget.TextView" />
    public class LinkifyTextView : TextView
    {
        /// <summary>
        /// Initialises a new instance of the <see cref="LinkifyTextView"/> class.
        /// </summary>
        /// <param name="context">The context.</param>
        public LinkifyTextView(Context context)
            : base(context)
        {
            this.Initialise();
        }

        /// <summary>
        /// Initialises a new instance of the <see cref="LinkifyTextView"/> class.
        /// </summary>
        /// <param name="context">The context.</param>
        /// <param name="attrs">The attributes.</param>
        public LinkifyTextView(Context context, IAttributeSet attrs)
            : base(context, attrs)
        {
            this.Initialise();
        }

        /// <summary>
        /// Initialises a new instance of the <see cref="LinkifyTextView"/> class.
        /// </summary>
        /// <param name="context">The context.</param>
        /// <param name="attrs">The attributes.</param>
        /// <param name="defStyleAttr">The definition style attribute.</param>
        public LinkifyTextView(Context context, IAttributeSet attrs, int defStyleAttr)
            : base(context, attrs, defStyleAttr)
        {
            this.Initialise();
        }

        /// <summary>
        /// Initialises a new instance of the <see cref="LinkifyTextView"/> class.
        /// </summary>
        /// <param name="context">The context.</param>
        /// <param name="attrs">The attributes.</param>
        /// <param name="defStyleAttr">The definition style attribute.</param>
        /// <param name="defStyleRes">The definition style resource.</param>
        public LinkifyTextView(Context context, IAttributeSet attrs, int defStyleAttr, int defStyleRes)
            : base(context, attrs, defStyleAttr, defStyleRes)
        {
            this.Initialise();
        }

        /// <summary>
        /// Initialises a new instance of the <see cref="LinkifyTextView"/> class.
        /// </summary>
        /// <param name="javaReference">The java reference.</param>
        /// <param name="transfer">The transfer.</param>
        protected LinkifyTextView(System.IntPtr javaReference, JniHandleOwnership transfer)
            : base(javaReference, transfer)
        {
            this.Initialise();
        }

        /// <inheritdoc/>
        public override bool OnTouchEvent(MotionEvent e)
        {
            if (e != null && this.TextFormatted is SpannableString buffer)
            {
                if (e.Action == MotionEventActions.Up || e.Action == MotionEventActions.Down)
                {
                    int x = (int)e.GetX();
                    int y = (int)e.GetY();

                    x -= this.TotalPaddingLeft;
                    y -= this.TotalPaddingTop;

                    x += this.ScrollX;
                    y += this.ScrollY;

                    Layout layout = this.Layout;
                    int line = layout.GetLineForVertical(y);
                    int off = layout.GetOffsetForHorizontal(line, x);

                    Object[] link = buffer.GetSpans(off, off, Class.FromType(typeof(ClickableSpan)));

                    if (link.Length != 0)
                    {
                        if (e.Action == MotionEventActions.Up)
                        {
                            ((ClickableSpan)link[0]).OnClick(this);
                        }
                        else if (e.Action == MotionEventActions.Down)
                        {
                            Selection.SetSelection(buffer, buffer.GetSpanStart(link[0]), buffer.GetSpanEnd(link[0]));
                        }

                        return true;
                    }
                }
            }

            return false;
        }

        /// <inheritdoc/>
        public override void SetText(ICharSequence text, BufferType type)
        {
            base.SetText(text, type);
            this.MovementMethod = default;
        }

        /// <summary>
        /// Initialises this instance.
        /// </summary>
        private void Initialise()
        {
            this.AutoLinkMask = MatchOptions.All;
        }
    }
}