不完整截图功能

using System;
using CoreGraphics;

using UIKit;
using Foundation;

using Pasasoft.Fep.Drawing;
using Pasasoft.Utilities;
using Pasasoft.Fep.Resources;
using Pasasoft.Localization;

namespace Pasasoft.Fep.UIKit
{
    public class ImageViewController:UIViewController
    {
        private UIImage image;

        private UIImageView imageView;

        private UIView maskView;

        public Action<UIImage> DoneAction{ get; set;}

        private UIBarButtonItem cropItem;
        private UIBarButtonItem rotationCW;
        private UIBarButtonItem rotationCCW;

        public ImageViewController()
        {
            var cancelButton = new UIBarButtonItem (UIBarButtonSystemItem.Cancel,null);
            cancelButton.Clicked += delegate {Dismiss();};

            NavigationItem.LeftBarButtonItem = cancelButton;

            var doneButton = new UIBarButtonItem (UIBarButtonSystemItem.Done, null);
            doneButton.Clicked += delegate {
                var image = GetTargetImage();
                if(null != image){
                    if(null != DoneAction)
                        DoneAction.Invoke(image);
                    Dismiss();
                }
                else{
                    AlertHelper.ShowAlert(Strings.CropRegion.Localize());
                }
            };
            NavigationItem.RightBarButtonItem = doneButton;

            cropItem = new UIBarButtonItem ();
            cropItem.Image=  UIImage.FromBundle (ImageFiles.Crop25);
            cropItem.Clicked += delegate {
                Crop();
            };

            rotationCW = new UIBarButtonItem ();
            rotationCW.Image = UIImage.FromBundle (ImageFiles.RotationCW);
            rotationCW.Clicked += delegate {
                Clear();
                Rotation(true);
            };

            rotationCCW = new UIBarButtonItem ();
            rotationCCW.Image = UIImage.FromBundle (ImageFiles.RotationCCW);
            rotationCCW.Clicked += delegate {
                Clear();
                Rotation(false);
            };

            ToolbarItems = new UIBarButtonItem[]{ cropItem, rotationCCW, rotationCW};

            EdgesForExtendedLayout = UIRectEdge.None;
        }

        private void Pan(UIPanGestureRecognizer gestureRecognizer)
        {
            if (null != maskView && maskView.Superview != null) {
                var p1 = gestureRecognizer.LocationInView (View);
                var p2 = gestureRecognizer.TranslationInView (View);

                var p3 = new CGPoint (p1.X - p2.X, p1.Y - p2.Y);
                var frame = DrawHelper.GetBound (p1, p3);
                maskView.Frame = frame;
            }
        }

        private UIImage GetTargetImage()
        {
            if (null == maskView || maskView.Superview == null)
                return image;

            var imageViewFrame = imageView.Frame;

            CGRect imageFrame = new CGRect ();
            var scaleImage = image.Size.Width / image.Size.Height;
            var scaleImageView = imageView.Frame.Width / imageView.Frame.Height;
            if (image.Size.Width < imageViewFrame.Width && image.Size.Height < imageViewFrame.Height) {
                imageFrame = imageViewFrame;
            }else if (scaleImageView > scaleImage) {
                var imageWidth = image.Size.Width / image.Size.Height * imageViewFrame.Height;
                var imageX = (imageViewFrame.Width - imageWidth) / 2;
                imageFrame = new CGRect (imageX, imageViewFrame.Y, imageWidth, imageViewFrame.Height);
            }else if (scaleImageView <= scaleImage) {
                var imageHeight = image.Size.Height / image.Size.Width * imageViewFrame.Width;
                var imageY = (imageViewFrame.Height - imageHeight) / 2;
                imageFrame = new CGRect (imageViewFrame.X, imageY, imageViewFrame.Width, imageHeight);
            }

            var frame = CGRect.Intersect(maskView.Frame,imageFrame);

            if (frame.IsEmpty)
                return null;
            var cropFrame = new CGRect ();
            var scaleX = image.Size.Width / imageFrame.Width;
            var scaleY = image.Size.Height / imageFrame.Height;
            cropFrame.X = (frame.X - imageFrame.X) * scaleX;
            cropFrame.Y = (frame.Y - imageFrame.Y) * scaleY;
            cropFrame.Width = frame.Width * scaleX;
            cropFrame.Height = frame.Height * scaleY;

            return image.Crop(cropFrame);
        }

        private void Clear()
        {
            if(null != maskView)
                maskView.RemoveFromSuperview ();

            cropItem.Image = UIImage.FromBundle (ImageFiles.Crop25);
            cropItem.Style = UIBarButtonItemStyle.Plain;
        }

        private void DoCrop()
        {
            if (null == maskView) {
                maskView = new UIView ();
                maskView.BackgroundColor = UIColor.FromRGB(0,0,96);
                maskView.Alpha = .5f;
            }

            maskView.Frame = CGRect.Empty;
            if(maskView.Superview == null)
                View.AddSubview (maskView);

            cropItem.Image = UIImage.FromBundle (ImageFiles.CropSelect25);
            cropItem.Style = UIBarButtonItemStyle.Done;
        }

        private void Crop()
        {
            if (cropItem.Style == UIBarButtonItemStyle.Plain)
                DoCrop ();
            else
                Clear ();
        }

        private void Rotation(bool isClockwise)
        {
            nfloat rotate, translateX, translateY;
            CGRect rect = new CGRect (0, 0, image.Size.Height, image.Size.Width);
            if (isClockwise) {
                rotate = 3 * (nfloat)Math.PI / 2;
                translateX = -rect.Size.Height;
                translateY = 0;
            } else {
                rotate = (nfloat)Math.PI / 2;
                translateX = 0;
                translateY = -rect.Size.Width;
            }

            UIGraphics.BeginImageContext (rect.Size);
            CGContext context = UIGraphics.GetCurrentContext ();
            context.TranslateCTM ( 0, rect.Height);
            context.ScaleCTM (1, -1);
            context.RotateCTM (rotate);
            context.TranslateCTM (translateX, translateY);

            context.DrawImage (new CGRect (0, 0, rect.Size.Height, rect.Size.Width), image.CGImage);
            image = UIGraphics.GetImageFromCurrentImageContext ();
            imageView.Image = image;
        }

        private void Dismiss()
        {
            NavigationController.PresentingViewController.DismissViewController(true,null);
        }

        public UIImage Image
        {
            get{ return image; }
            set
            { 
                image = value;
                if (IsViewLoaded)
                    imageView.Image = image;
            }
        }


        public override void LoadView ()
        {
            var view = new UIView (UIScreen.MainScreen.Bounds);
            view.BackgroundColor = UIColor.White;


            if (null != image)
                imageView = new UIImageView (image);
            else
                imageView = new UIImageView (UIScreen.MainScreen.Bounds);
            imageView.TranslatesAutoresizingMaskIntoConstraints = false;
            imageView.ContentMode = UIViewContentMode.ScaleAspectFit;
            view.AddSubview (imageView);

            View = view;

            var gestureRecognizer = new UIPanGestureRecognizer (Pan);
            gestureRecognizer.MinimumNumberOfTouches = 1;
            gestureRecognizer.MaximumNumberOfTouches = 1;
            view.AddGestureRecognizer (gestureRecognizer);
        }

        public override void ViewDidLayoutSubviews ()
        {
            base.ViewDidLayoutSubviews ();

            var rect = UIScreen.MainScreen.Bounds;
            var naviHeight = this.NavigationController.NavigationBar.Frame.Bottom + this.NavigationController.Toolbar.Frame.Height;
            imageView.Frame = new CGRect (0, 0, rect.Width, rect.Height - naviHeight);
        }
    }
}