ALAssetsLibrary writeImageToSavedPhotosAlbum阻止iOS8中的程序

Question

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingMediaWithInfo:(NSDictionary *)info
{
    NSMutableDictionary* meta = [[NSMutableDictionary alloc] initWithDictionary:[info objectForKey:UIImagePickerControllerMediaMetadata]];
    UIImage* img = [info objectForKey:UIImagePickerControllerOriginalImage];
if(self.locationManager.location){
        NSDictionary* locationMeta = [self gpsDictionaryForLocation:self.locationManager.location];
        [meta setObject:locationMeta forKey:(NSString*)kCGImagePropertyGPSDictionary];
    }

    ALAssetsLibrary* library = [[ALAssetsLibrary alloc] init];

    [library writeImageToSavedPhotosAlbum:img.CGImage metadata:meta completionBlock:^(NSURL* assetUrl, NSError* error){
        //.......
    }
    [picker dismissViewControllerAnimated:YES completion:nil];
}

此代码在iOS7中运行良好。将设备升级到iOS8后，程序被阻止，imagePickerView没有被解雇。

这是iOS8中的错误吗？有人可以帮帮我吗？