Xamarin.iOS Extension Methods

ExtensionMethods.cs

using System;
using MonoTouch.UIKit;

namespace System
{
  public static class ExtensionMethods
  {
    public static UIColor ToUIColor(this string hexString)
    {
        hexString = hexString.Replace("#", "");

        if (hexString.Length == 3)
            hexString = hexString + hexString;

        if (hexString.Length != 6)
            throw new Exception("Invalid hex string");

        int red = Int32.Parse(hexString.Substring(0,2), System.Globalization.NumberStyles.AllowHexSpecifier);
        int green = Int32.Parse(hexString.Substring(2,2), System.Globalization.NumberStyles.AllowHexSpecifier);
        int blue = Int32.Parse(hexString.Substring(4,2), System.Globalization.NumberStyles.AllowHexSpecifier);

        return UIColor.FromRGB(red, green, blue);
    }

    public static SizeF StringSize(this UILabel label)
    {
        return new NSString(label.Text).StringSize(label.Font);
    }


    public static void HideGradientBackground(this UIView view)
    {
        try
        {
            foreach(var subview in view.Subviews)
            {
                if(subview.GetType() == typeof(UIImageView))
                    subview.Hidden = true;
                subview.HideGradientBackground();
            }
        }
        catch
        {
            // nothing to do
        }
    }

    /// <summary>
    /// Returns a lighter color
    /// </summary>
    /// <param name="steps">The number of steps to lighten.</param>
    public static UIColor Lighten(this UIColor color, int steps)
    {
        int modifier = 16 * steps;

        float rF, gF, bF, aF;
        color.GetRGBA(out rF, out gF, out bF, out aF);

        int r, g, b, a;
        r = (int)Math.Ceiling(rF * 255);
        g = (int)Math.Ceiling(gF * 255);
        b = (int)Math.Ceiling(bF * 255);
        a = (int)Math.Ceiling(aF * 255);

        r += modifier;
        g += modifier;
        b += modifier;
        // leave 'a' alone?

        r = r > 255 ? 255 : r;
        g = g > 255 ? 255 : g;
        b = b > 255 ? 255 : b;

        return UIColor.FromRGBA(r, g, b, a);
    }

    /// <summary>
    /// Returns a darker color
    /// </summary>
    /// <param name="steps">The number of steps to darken.</param>
    public static UIColor Darken(this UIColor color, int steps)
    {
        int modifier = 16 * steps;

        float rF, gF, bF, aF;

        color.GetRGBA(out rF, out gF, out bF, out aF);

        int r, g, b, a;
        r = (int)Math.Ceiling(rF * 255);
        g = (int)Math.Ceiling(gF * 255);
        b = (int)Math.Ceiling(bF * 255);
        a = (int)Math.Ceiling(aF * 255);

        r -= modifier;
        g -= modifier;
        b -= modifier;
        // leave 'a' alone?

        r = r < 0 ? 0 : r;
        g = g < 0 ? 0 : g;
        b = b < 0 ? 0 : b;

        return UIColor.FromRGBA(r, g, b, a);
    }
  }
}

Line 13 is wrong:

hexString = hexString + hexString;

It works for #333, but doesn't work for #123 where #123123 - is a different color.

I think the intent must be to double each digit, right? So:

#333 => 3+3, 3+3, 3+3 => #333333
#123 => 1+1, 2+2, 3+3 => #112233