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(_1);  // an NSURL that references an

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