iOS 从相机或相册获取图片并裁剪

今天遇到一个用户头像上传的问题，需要从相册或者相机中读取图片。代码很简单，抽取关键部分，如下：

//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