//圆角头像

 _avatarView = new UIImageView(new RectangleF(_blockSpace, _blockSpace, 2 * _avatarRadius, 2 * _avatarRadius));

UIImage img = UIImage.FromFile("profile-pic.jpg");

_avatarView.Layer.Contents = img.CGImage;

_avatarView.Layer.MasksToBounds = true;//如果没有将MasksToBounds设置为true，图片圆角无效

_avatarView.Layer.CornerRadius = _avatarRadius;

 _avatarView.UserInteractionEnabled = true;//用户互动属性()

_avatarView.AddGestureRecognizer(new UITapGestureRecognizer(onClickImage));

 void onClickImage()

 {

            try

            {

                //UIActionSheet是在iOS弹出的选择按钮项的对话框，可以添加多项，并为每项添加点击事件。

                //ChangePictureActionSheetDelegate：通过重写UIActionSheetDelegate的Clicked方法，获取当前点击项

                UIActionSheet _actionSheet = new UIActionSheet("选择图片",

                new ChangePictureActionSheetDelegate(this,_avatarView), "取消",

                null, "从相片库", "拍照");

                _actionSheet.ShowInView(this.View);

            }

            catch (Exception e)

            {

                Console.WriteLine("Error:" + e.Message);

            }

 }

class ChangePictureActionSheetDelegate : UIActionSheetDelegate

    {

        UIViewController _controller;

        UIImageView _img;

        UIImagePickerController picker;

        public ChangePictureActionSheetDelegate(UIViewController controller,UIImageView img)

        {

            _controller = controller;

            _img = img;

        }

        public override void Clicked(UIActionSheet actionSheet, int buttonIndex)

        {

            Console.WriteLine("你选择了：" + buttonIndex);

            switch (buttonIndex)

            {

                case 1: CallPhoto(UIImagePickerControllerSourceType.Camera); break;

                case 0: CallPhoto(UIImagePickerControllerSourceType.PhotoLibrary); break;

                default: break;

            }

        }        

        private void CallPhoto(UIImagePickerControllerSourceType type)

        {

            Console.WriteLine("Begin...");

            if (UIImagePickerController.IsSourceTypeAvailable(type))

            {

                try

                {

                    picker = new UIImagePickerController();

                    picker.SourceType = type;

                    //允许编辑图片

                    picker.AllowsEditing = true;

                    if (_controller.PresentedViewController == null)

                    {

                        _controller.PresentModalViewController(picker, false);

                    }

                    //picker.FinishedPickingImage += picker_FinishedPickingImage;(无效)

                    //AvatarPickerDelegate：通过重写UIImagePickerControllerDelegate的FinishedPickingImage方法获取选择的图片

                    picker.Delegate =new AvatarPickerDelegate(_img);

                    Console.WriteLine("Finished");

                }

                catch (Exception e)

                {

                    Console.WriteLine("Error:" + e.Message);

                }

            }

            else

            {

                Console.WriteLine("该设备不支持此操作");

            }

        }

    }

class AvatarPickerDelegate:UIImagePickerControllerDelegate {

        UIImageView _avatar;

        public AvatarPickerDelegate(UIImageView _imgView) {

            _avatar = _imgView;

        }

        public override void FinishedPickingImage(UIImagePickerController picker, UIImage image, NSDictionary editingInfo)

        {

            Console.WriteLine("选择了图片");

            if (image == null)

            {

                Console.WriteLine("Null");

            }

           //更新显示图片

            _avatar.Layer.Contents = image.CGImage;

            //关闭UIImagePicker

            picker.DismissModalViewControllerAnimated(true);

            Console.WriteLine("完成选择");

        }

    }