C# ColorTranslator.FromHtml() throws Exception for "Grey" (is not a valid value for int32)

Question

I am using the Microsoft Cognitive Services / Vision API in my application.

Vision API returns colours as string - either HEX (without the "#" prefix), or as a Name.

In order to convert this to a System.Drawing.Color that I can use as a panel background color, I am using the below code:

// Hex Color Format
Regex hex = new Regex("^#(?:[0-9a-fA-F]{3}){1,2}$");

// Colours
System.Drawing.Color accent = new System.Drawing.Color();
System.Drawing.Color fore = new System.Drawing.Color();
System.Drawing.Color back = new System.Drawing.Color();

try
{
  if (hex.IsMatch("#" + result.Color.AccentColor.ToString())) accent = ColorTranslator.FromHtml("#" + result.Color.AccentColor.ToString());
  else accent = ColorTranslator.FromHtml(result.Color.AccentColor.ToString());

  fore = ColorTranslator.FromHtml(result.Color.DominantColorForeground.ToString());
  back = ColorTranslator.FromHtml(result.Color.DominantColorBackground.ToString());

  displayData.Colors = new System.Drawing.Color[] { accent, fore, back };

}
catch (Exception e)
{
  throw new Exception(e.Message.ToString());
}

This has worked fine in 99% of cases, however, when one of the Colors returns from Micrsoft Vision API with "Grey", I get an Exception:

Grey is not a valid value for Int32

(This is the only color name I've encountered but I don't know if there would be others)

From my understanding, this would be because "Grey" is not a HTML Color Name, as it should be "Gray" ("Grey" being the CSS name) http://www.rapidtables.com/web/color/gray-color.htm

What would be the best way to handle this Exception? I was thinking creating a Dictionary of "bad" color names and manually assign those colors their true HTML Color Name (or a System.Drawing.Color directly), but this seems prone to human error and a constant game of update the Color.

Thoughts? Thanks.

Answer 1

I probably did this is in a convoluted manner, but I merged all of your responses into one and I think it was a neat solution:

I create a new class called ColorFix, which checks for "bad" names in a Dictionary<string, string> (manually defined), then checks if it is a KnownName, before otherwise just returning a new blank Color object.

Then, from the calling class, I created a Method ColorFromString which accepts the raw string color from the Microsoft API.

This is the old code that tries to ColorTranslate.FromHtml -- and catches Exceptions -- except now Exceptions are processed through ColorFix.

So round-about way of just parsing through a Dictionary and Checking if it's a KnownName.

I'm relatively new to C#, so here is my code if this helps anyone:

Controller.cs

        // Colours
        System.Drawing.Color accent = new System.Drawing.Color();
        System.Drawing.Color fore = new System.Drawing.Color();
        System.Drawing.Color back = new System.Drawing.Color();

        try
        {
            accent = ColorFromString(result.Color.AccentColor.ToString());
            fore = ColorFromString(result.Color.DominantColorForeground.ToString());
            back = ColorFromString(result.Color.DominantColorBackground.ToString());

            displayData.Colors = new System.Drawing.Color[] { accent, fore, back };
        }
        catch (Exception e)
        {
            throw new Exception(e.Message.ToString());
        }

...

    private System.Drawing.Color ColorFromString(string color)
    {
        System.Drawing.Color value = new System.Drawing.Color();

        // Hex Color Format
        Regex hex = new Regex("^#(?:[0-9a-fA-F]{3}){1,2}$");

        try
        {
            if (hex.IsMatch("#" + color)) value = ColorTranslator.FromHtml("#" + color);
            else value = ColorTranslator.FromHtml(color);
        }
        catch (Exception)
        {
            ColorFix colorFix = new ColorFix(color);

            value = colorFix.Fix();
        }

        return value;
    }

ColorFix.cs

using System;
using System.Collections.Generic;
using System.Drawing;

namespace Project.Services
{
    class ColorFix
    {
        private string color;
        public Dictionary<string, string> badColors = new Dictionary<string, string>(StringComparer.InvariantCultureIgnoreCase);

        //
        // Constructor, takes Color String
        //
        // @param string(color)
        // @return void
        //
        public ColorFix(string color)
        {
            this.color = color;

            badColors.Add("Grey", "Gray");
        }

        //
        // Fix the Color Exception
        //
        // @return Color
        //
        public Color Fix()
        {
            if (Bad() != null) return (Color)Bad();
            if (Known() != null) return (Color)Known();

            return new Color();
        }

        //
        // Check if Color is a system KnownColor
        //
        // @return Nullable<Color>
        //
        private Color? Known()
        {
            string colorLower = color.ToLower();

            Array colorValues = Enum.GetValues(typeof(KnownColor));
            string[] colorNames = Enum.GetNames(typeof(KnownColor));

            for (int c = 0; c < colorValues.Length; c++)
            {
                if (colorNames.Equals(colorLower)) return Color.FromKnownColor((KnownColor)colorValues.GetValue(c));
            }

            return null;
        }

        //
        // Check if Color is within the Bad Colors Dictionary
        //
        // @return Nullable<Color>
        //
        private Color? Bad()
        {
            if (badColors.ContainsKey(color))
            {
                try
                {
                    return ColorTranslator.FromHtml(badColors[color]);
                }
                catch (Exception)
                {
                    return null;
                }
            }

            return null;
        }
    }
}