IOS 判断相册是否允许访问

ALAssetsLibrary *library = [[ALAssetsLibrary alloc]init];
    [library writeImageToSavedPhotosAlbum:image.CGImage orientation:image.imageOrientation completionBlock:^(NSURL *asSetUrl,NSError *error){
        if (error) {
            UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"保存图片失败"
                                                           message:@"请打开 设置-隐私-照片 来进行设置"
                                                          delegate:nil
                                                 cancelButtonTitle:@"确定"
                                                 otherButtonTitles:nil, nil];
            [alert show];
            [alert release];
        }else{
            UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"保存图片成功"
                                                           message:nil
                                                          delegate:nil
                                                 cancelButtonTitle:@"确定"
                                                 otherButtonTitles:nil, nil];
            [alert show];
            [alert release];
        }

    }];