iOS 從相機或相冊獲取圖片并裁剪

    //load user image


- (void)UesrImageClicked  
{  
    UIActionSheet *sheet;  

    // 判斷是否支持相機  
    if([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera])  
    {  
        sheet  = [[UIActionSheet alloc] initWithTitle:@"選擇圖像" delegate:self cancelButtonTitle:nil destructiveButtonTitle:@"取消" otherButtonTitles:@"拍照", @"從相冊選擇", nil];  
    }  
    else {  
        sheet = [[UIActionSheet alloc] initWithTitle:@"選擇圖像" delegate:self cancelButtonTitle:nil destructiveButtonTitle:@"取消" otherButtonTitles:@"從相冊選擇", 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;  
        // 判斷是否支持相機  
        if([UIImagePickerController isSourceTypeAvailable:UIImagePickerControllerSourceTypeCamera]) {  
            switch (buttonIndex) {  
                case 0:  
                    return;  
                case 1: //相機  
                    sourceType = UIImagePickerControllerSourceTypeCamera;  
                    break;  
                case 2: //相冊  
                    sourceType = UIImagePickerControllerSourceTypePhotoLibrary;  
                    break;  
            }  
        }  
        else {  
            if (buttonIndex == 0) {  
                return;  
            } else {  
                sourceType = UIImagePickerControllerSourceTypeSavedPhotosAlbum;  
            }  
        }  
        // 跳轉到相機或相冊頁面  
        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];  

}  </pre><br />

創建一張表單，選擇相機或者相冊，然后用回調函數處理返回的圖片。
 
但是返回的圖像并不是正方形，顯示在用戶頭像的View里面產生明顯的拉伸。研究了很久各種裁剪算法，甚至想創建一個view來處理。突然發現代碼中從相機、相冊獲取圖片時采用的的
UIImagePickerControllerOriginalImage
于是跟蹤進去一看：
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，很簡單，用UIImagePickerControllerEditedImage，萬事搞定。