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

UIKIT_EXTERNNSString *const UIImagePickerControllerOriginalImage; // a UIImage

UIKIT_EXTERNNSString *const UIImagePickerControllerEditedImage;   // a UIImage

UIKIT_EXTERNNSString *const UIImagePickerControllerCropRect;      // an NSValue (CGRect)

UIKIT_EXTERNNSString *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。