Xamarin.Forms.Color to hex value

Just a quick fix, the last line is wrong.

Alpha channel comes before the other values:

string hex = String.Format("#{0:X2}{1:X2}{2:X2}{3:X2}", alpha, red, green, blue);

and this is best for an extension method:

public static class ExtensionMethods
{
    public static string GetHexString(this Xamarin.Forms.Color color)
    {
        var red = (int)(color.R * 255);
        var green = (int)(color.G * 255);
        var blue = (int)(color.B * 255);
        var alpha = (int)(color.A * 255);
        var hex = $"#{alpha:X2}{red:X2}{green:X2}{blue:X2}";

        return hex;
    }
}

a bit late but here is how I do that in Xamarin Forms (the Xamarin.Forms.Color class already exposes a FromHex(string) method.

public string ColorHexa { get; set; }
public Color Color
{
    get => Color.FromHex(ColorHexa);
    set => ColorHexa = value.ToHexString();
}

With this extension :

public static class ColorExtensions
{
    public static string ToHexString(this Color color, bool outputAlpha = true)
    {
        string DoubleToHex(double value)
        {
            return string.Format("{0:X2}", (int)(value * 255));
        }

        string hex = "#";
        if (outputAlpha) hex += DoubleToHex(color.A);
        return $"{hex}{DoubleToHex(color.R)}{DoubleToHex(color.G)}{DoubleToHex(color.B)}";
    }
}

var color = Xamarin.Forms.Color.Orange;
int red = (int) (color.R * 255);
int green = (int) (color.G * 255);
int blue = (int) (color.B * 255);
int alpha = (int)(color.A * 255);
string hex = String.Format("#{0:X2}{1:X2}{2:X2}{3:X2}", red, green, blue, alpha);