iOS helper functions in Xamarin

color-from-hex

        // http://stackoverflow.com/questions/10310917/uicolor-from-hex-in-monotouch
        public static UIColor GetColorFromHexString(string hexValue) {
            hexValue = hexValue.Substring(1, 6); // string will be passed in with a leading #
            var r = Convert.ToByte(hexValue.Substring(0, 2), 16);
            var g = Convert.ToByte(hexValue.Substring(2, 2), 16);
            var b = Convert.ToByte(hexValue.Substring(4, 2), 16);
            return UIColor.FromRGB(r, g, b);
        }

crop-square-uiimage

        //http://forums.xamarin.com/discussion/14269/objective-c-image-crop-function
        public static UIImage CropSquare(UIImage image) {
            var dimension = Math.Min((float)image.Size.Height, (float)image.Size.Width);
            float x = ((float)image.Size.Width / 2) - (dimension / 2);
            if (x < 0) { x = 0; }
            float y = ((float)image.Size.Height / 2) - (dimension / 2);
            if (y < 0) { y = 0; }
            RectangleF rect = new RectangleF(x, y, dimension, dimension);

            using (CGImage cgcrop = image.CGImage.WithImageInRect(rect)) {
                UIImage cropped = UIImage.FromImage(cgcrop);
                return cropped;
            }
        }

iOS-version

        //http://blog.xamarin.com/ios-6-7-compatibility-tips/
        public static bool IsiOS7OrHigher {
            get { return UIDevice.CurrentDevice.CheckSystemVersion(7, 0); }
        }

        public static bool IsiOS8OrHigher {
            get { return UIDevice.CurrentDevice.CheckSystemVersion(8, 0); }
        }

move-next-textField

        // bit hackish I feel, but works mostly
        public static bool MoveToNextTextField(UITextField textField) {
            int nextTag = textField.Tag + 1;
            UIResponder nextResponder = textField.Superview.ViewWithTag(nextTag);
            if(nextResponder != null) {
                nextResponder.BecomeFirstResponder();
            }
            else {
                textField.ResignFirstResponder();
            }
            return false;
        }

pictures-folder

        public static string GetPicturesFolder() {
            string picturesFolder;
            //if (IsiOS8OrHigher) { // Xamarin suggested iOS8 support, but appears unnecessary at last time we checked
            //    picturesFolder = NSFileManager.DefaultManager.GetUrls(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomain.User)[0].ToString();
            //}
            //else {
                picturesFolder = Environment.GetFolderPath(Environment.SpecialFolder.Personal);
            //}
            return picturesFolder;
        }

row-height

        //http://stackoverflow.com/questions/8344596/monotouch-uitableviewcell-height
        // StringSize now deprecated. See this forum post http://forums.xamarin.com/discussion/8154/uitextview-contentheight, 
        // specifically this answer from a xamarin employee http://forums.xamarin.com/discussion/comment/29997/#Comment_29997
        // Table cells that don't use the full cell width need an adjustment.
        public static float GetViewHeight(UIView view, string viewText, float fontSize = 12f, int viewWidthAdjustment = 0) {
            if (Utils.IsiOS7OrHigher) {
                var text = new NSMutableAttributedString(viewText);
                text.AddAttribute(UIStringAttributeKey.Font, UIFont.SystemFontOfSize(fontSize), new NSRange(0, text.Length));
                var ctxt = new NSStringDrawingContext();
                var boundingRect = text.GetBoundingRect(new SizeF(view.Frame.Width - viewWidthAdjustment, float.MaxValue), NSStringDrawingOptions.UsesFontLeading | NSStringDrawingOptions.UsesLineFragmentOrigin, ctxt);
                //Add some padding 
                return boundingRect.Height + 24;
            }
            else {
                string item = viewText;
                SizeF size = new SizeF(view.Frame.Width - viewWidthAdjustment, float.MaxValue);
                // TODO: if the font size of the table row items change in the storyboard, make sure this changes too
                float height = view.StringSize(item, UIFont.SystemFontOfSize(fontSize), size, UILineBreakMode.WordWrap).Height + 24;
                return height;
            }
        }

scale-uiimage

        // scale image, maintain aspect ratio
        public static UIImage Scale(UIImage image, int limitingDimension) {
            float scaleFactor = Math.Max(limitingDimension / image.Size.Height, limitingDimension / image.Size.Width);
            if(scaleFactor > 1) {
                return image;
            }
            return image.Scale(new SizeF(image.Size.Width * scaleFactor, image.Size.Height * scaleFactor));
        }

uialertview-task

        // Displays a UIAlertView and returns the index of the button pressed.
        public static Task<int> ShowAlert(string title, string message, params string[] buttons) {
            var tcs = new TaskCompletionSource<int>();
            var alert = new UIAlertView {
                Title = title,
                Message = message
            };
            foreach(var button in buttons)
                alert.AddButton(button);
            alert.Clicked += (s, e) => tcs.TrySetResult(e.ButtonIndex);
            alert.Show();
            return tcs.Task;
        }