Manipulates a URI to get a resolution appropriate image by convention (for iOS) before calling Xamarin.Forms.ImageSource.FromUri(...)

UriImageLoaderIos.cs

    public class UriImageLoaderIos : IUriImageLoader
    {
        public string GetUri(string baseImageUri)
        {
            if (string.IsNullOrEmpty(baseImageUri))
            {
                throw new ArgumentNullException("baseImageUri");
            }
            if (UIScreen.MainScreen.Scale > 2.0)
            {
                return InsertMultiplierBeforeSuffix(baseImageUri, "@3x");
            }
            else if (UIScreen.MainScreen.Scale > 1.0)
            {
                return InsertMultiplierBeforeSuffix(baseImageUri, "@2x");
            }
            else
            {
                return baseImageUri;
            }
        }

        private string InsertMultiplierBeforeSuffix(string baseImageUri, string multiplier)
        {
            var lastDotIndex = baseImageUri.LastIndexOf(".");
            if (lastDotIndex == -1)
            {
                throw new ArgumentException("Invalid file name: " + baseImageUri, baseImageUri);
            }
            return baseImageUri.Insert(lastDotIndex, multiplier);
        }