iOS 从相机或相册获取图片并裁剪

    //load user image        - (void)UesrImageClicked        {            UIActionSheet *sheet;                        // 判断是否支持相机            if([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera])            {                sheet  = [[UIActionSheet alloc] initWithTitle:@"选择图像" delegate:self cancelButtonTitle:nil destructiveButtonTitle:@"取消" otherButtonTitles:@"拍照", @"从相册选择", nil];            }            else {                sheet = [[UIActionSheet alloc] initWithTitle:@"选择图像" delegate:self cancelButtonTitle:nil destructiveButtonTitle:@"取消" otherButtonTitles:@"从相册选择", nil];            }                        sheet.tag = 255;                        [sheet showInView:self.view];        }                        #pragma mark - action sheet delegte        - (void)actionSheet:(UIActionSheet *)actionSheet clickedButtonAtIndex:(NSInteger)buttonIndex        {            if (actionSheet.tag == 255) {                NSUInteger sourceType = UIImagePickerControllerSourceTypePhotoLibrary;                // 判断是否支持相机                if([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) {                    switch (buttonIndex) {                        case 0:                            return;                        case 1: //相机                            sourceType = UIImagePickerControllerSourceTypeCamera;                            break;                        case 2: //相册                            sourceType = UIImagePickerControllerSourceTypePhotoLibrary;                            break;                    }                }                else {                    if (buttonIndex == 0) {                        return;                    } else {                        sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;                    }                }                // 跳转到相机或相册页面                UIImagePickerController *imagePickerController = [[UIImagePickerController alloc] init];                imagePickerController.delegate = self;                imagePickerController.allowsEditing = YES;                imagePickerController.sourceType = sourceType;                                [self presentViewController:imagePickerController animated:YES completion:^{}];            }        }                #pragma mark - image picker delegte        - (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info        {            [picker dismissViewControllerAnimated:YES completion:^{}];                        UIImage *image = [info UIImagePickerControllerOriginalImage];                userImageView.image = image;                        NSData *imageData = UIImageJPEGRepresentation(image, COMPRESSED_RATE);            UIImage *compressedImage = [UIImage imageWithData:imageData];                        [HttpRequestManager uploadImage:compressedImage httpClient:self.httpClient delegate:self];                    }  

创建一张表单，选择相机或者相册，然后用回调函数处理返回的图片。

但是返回的图像并不是正方形，显示在用户头像的View里面产生明显的拉伸。研究了很久各种裁剪算法，甚至想创建一个view来处理。突然发现代码中从相机、相册获取图片时采用的的

UIImagePickerControllerOriginalImage

于是跟踪进去一看：

UIKIT_EXTERN NSString *const UIImagePickerControllerMediaType;     // an NSString (UTI, i.e. kUTTypeImage)

UIKIT_EXTERN NSString *const UIImagePickerControllerOriginalImage; // a UIImage

UIKIT_EXTERN NSString *const UIImagePickerControllerEditedImage;   // a UIImage

UIKIT_EXTERN NSString *const UIImagePickerControllerCropRect;      // an NSValue (CGRect)

UIKIT_EXTERN NSString *const UIImagePickerControllerMediaURL;      // an NSURL

UIKIT_EXTERN NSString *const UIImagePickerControllerReferenceURL       NS_AVAILABLE_IOS(4_1); // an NSURL that references an 

恍然大悟，很简单，用UIImagePickerControllerEditedImage，万事搞定。