1、C语言方法

在需要保存图片的代码中调用下列方法即可

    UIImageWriteToSavedPhotosAlbum(self.imageView.image, self, @selector(image:didFinishSavingWithError:contextInfo:), nil);

注意：在上诉select方法中必须要按规定调用下列方法才可以，不可以自定义方法，否则会编译报错

- (void)image:(UIImage *)image didFinishSavingWithError:(NSError *)error contextInfo:(void *)contextInfo
{
    if (error) {
        [SVProgressHUD showErrorWithStatus:@"图片保存失败！！！"];
    } else {
        [SVProgressHUD showSuccessWithStatus:@"图片保存成功！"];
    }
}

2、Photos库

PHAsset：一张相片或者一个视频
PHAssetCollection：一个相册
相片和相册的操作共有4中情况：增删改查，其中增删改归纳为1类，查归纳为1类；
所有的增删改操作都需要在-[PHPhotoLibrary performChanges:] 或者 -[PHPhotoLibrary performChangesAndWait:] block方法中执行，否者会编译报错

用户保存一张图片到自定义相册代码示例

    // 获取保存到相册的图片
    PHFetchResult<PHAsset *> *createdAssets = [self createdAssets];
    if (createdAssets == nil) {
        [SVProgressHUD showErrorWithStatus:@"保存图片失败!!!"];
        return;
    }
    
    // 查找自定义相册
    PHAssetCollection *collect = [self createdCollection];
    if (collect == nil) {
        [SVProgressHUD showErrorWithStatus:@"自定义相册创建失败"];
        return;
    }
    
    // 保存图片到自定义相册
    [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
        PHAssetCollectionChangeRequest *request = [PHAssetCollectionChangeRequest changeRequestForAssetCollection:collect];
        [request insertAssets:createdAssets atIndexes:[NSIndexSet indexSetWithIndex:0]];
    } error:&error];
    
    if (error) {
        [SVProgressHUD showErrorWithStatus:@"保存图片到自定义相册失败"];
    } else {
        [SVProgressHUD showSuccessWithStatus:@"保存图片到自定义相册成功"];
    }

查找自定义相册方法，如果自定义相册不存在，则创建一个自定义相册并返回

- (PHAssetCollection *)createdCollection
{
    // 取出软件名称
    NSString *title = [NSBundle mainBundle].infoDictionary[(NSString *)kCFBundleNameKey];
    
    // 获取相册集
    PHFetchResult<PHAssetCollection *> *collects = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeAlbum subtype:PHAssetCollectionSubtypeAlbumRegular options:nil];
    // 遍历相册集，查找自定义相册
    for (PHAssetCollection *collect in collects) {
        if ([collect.localizedTitle isEqualToString:title]) {
            return collect;
        }
    }
    
    NSError *error = nil;
    __block NSString * createdcollectID = nil;
    
    // 遍历相册集没有找到自定义相册，创建一个自定义相册
    [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
        // 创建一个自定义相册，并返回Identifier
        createdcollectID = [PHAssetCollectionChangeRequest creationRequestForAssetCollectionWithTitle:title].placeholderForCreatedAssetCollection.localIdentifier;
    } error:&error];
    
    if (error) {
        return nil;
    } else {
        [SVProgressHUD showSuccessWithStatus:@"相册创建成功"];
    }
    
    // 通过相册的Identifier快速遍历相册集并返回相册
    return [PHAssetCollection fetchAssetCollectionsWithLocalIdentifiers:@[createdcollectID] options:nil].firstObject;
}

获取保存到相册的图片方法，保存图片到相册并返回图片

- (PHFetchResult<PHAsset *> *)createdAssets
{
    NSError *error = nil;
    __block NSString * assetID = nil;
    
    [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
        // 保存图片，并获取保存图片的Identifier
        assetID = [PHAssetChangeRequest creationRequestForAssetFromImage:self.imageView.image].placeholderForCreatedAsset.localIdentifier;
    } error:&error];
    
    if (error) {
        return nil;
    }
    
    // 通过图片的Identifier快速遍历图片并返回图片
    return [PHAsset fetchAssetsWithLocalIdentifiers:@[assetID] options:nil];
}

注意事项，在保存图片的时候需要确定是否有判断APP是否有权限访问相册，可调用以下方法根据返回状态进行判断

(void)requestAuthorization:(void(^)(PHAuthorizationStatus status))handler