一、 C语言函数UIImageWriteToSavedPhotosAlbum

- (IBAction)save {
    UIImageWriteToSavedPhotosAlbum(self.imageView.image, self, @selector(image:didFinishSavingWithError:contextInfo:), nil);
}

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

二、Photos

• 1、PHAsset : 一个PHAsset对象就代表相册中的一张图片或者一个视频。
  查 : [PHAsset fetchAssets...]
  增删改 : PHAssetChangeRequest(包括图片\视频相关的所有改动操作)

• 2、PHAssetCollection : 一个PHAssetCollection对象就代表一个相册
  查 : [PHAssetCollection fetchAssetCollections...]
  增删改 : PHAssetCollectionChangeRequest(包括相册相关的所有改动操作)

• 3、 对相片\相册的任何【增删改】操作，都必须放到以下方法的block中执行：
  -[PHPhotoLibrary performChanges:completionHandler:]
  -[PHPhotoLibrary performChangesAndWait:error:]

 #1、异步执行修改操作
 [[PHPhotoLibrary sharedPhotoLibrary] performChanges:^{
 [PHAssetChangeRequest creationRequestForAssetFromImage:self.imageView.image];
 } completionHandler:^(BOOL success, NSError * _Nullable error) {
 if (error) {
 [SVProgressHUD showErrorWithStatus:@"保存失败！"];
 } else {
 [SVProgressHUD showSuccessWithStatus:@"保存成功！"];
 }
 }];

 #2、同步执行修改操作
 NSError *error = nil;
 [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
 [PHAssetChangeRequest creationRequestForAssetFromImage:self.imageView.image];
 } error:&error];
 if (error) {
 [SVProgressHUD showErrorWithStatus:@"保存失败！"];
 } else {
 [SVProgressHUD showSuccessWithStatus:@"保存成功！"];
 }

三、请求检查访问权限 :

• 如果用户还没有做出选择，会自动弹框，用户对弹框做出选择后，才会调用block。
• 如果之前已经做过选择，会直接执行block。

    [PHPhotoLibrary requestAuthorization:^(PHAuthorizationStatus status) {
        dispatch_async(dispatch_get_main_queue(), ^{
            if (status == PHAuthorizationStatusDenied) { // 用户拒绝当前App访问相册
                if (oldStatus != PHAuthorizationStatusNotDetermined) {
                    NSLog(@"提醒用户打开开关");
                }
            } else if (status == PHAuthorizationStatusAuthorized) { // 用户允许当前App访问相册
                [self saveImageIntoAlbum];
            } else if (status == PHAuthorizationStatusRestricted) { // 无法访问相册
                [SVProgressHUD showErrorWithStatus:@"因系统原因，无法访问相册！"];
            }
        });
    }];

四、示例

#pragma mark -     请求\检查访问权限 :
- (IBAction)save {
    PHAuthorizationStatus oldStatus = [PHPhotoLibrary authorizationStatus];

   [PHPhotoLibrary requestAuthorization:^(PHAuthorizationStatus status) {
        dispatch_async(dispatch_get_main_queue(), ^{
            if (status == PHAuthorizationStatusDenied) { // 用户拒绝当前App访问相册
                if (oldStatus != PHAuthorizationStatusNotDetermined) {
                    NSLog(@"提醒用户打开开关");
                }
            } else if (status == PHAuthorizationStatusAuthorized) { // 用户允许当前App访问相册
                [self saveImageIntoAlbum];
            } else if (status == PHAuthorizationStatusRestricted) { // 无法访问相册
                [SVProgressHUD showErrorWithStatus:@"因系统原因，无法访问相册！"];
            }
        });
    }];
}
#pragma mark -   保存图片到相册
- (void)saveImageIntoAlbum
{
    // 获得相片
    PHFetchResult<PHAsset *> *createdAssets = self.createdAssets;
    if (createdAssets == nil) {
        [SVProgressHUD showErrorWithStatus:@"保存图片失败！"];
        return;
    }
    
    // 获得相册
    PHAssetCollection *createdCollection = self.createdCollection;
    if (createdCollection == nil) {
        [SVProgressHUD showErrorWithStatus:@"创建或者获取相册失败！"];
        return;
    }
    
    // 添加刚才保存的图片到【自定义相册】
    NSError *error = nil;
    [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
        PHAssetCollectionChangeRequest *request = [PHAssetCollectionChangeRequest changeRequestForAssetCollection:createdCollection];
        [request insertAssets:createdAssets atIndexes:[NSIndexSet indexSetWithIndex:0]];
    } error:&error];
    
    // 最后的判断
    if (error) {
        [SVProgressHUD showErrorWithStatus:@"保存图片失败！"];
    } else {
        [SVProgressHUD showSuccessWithStatus:@"保存图片成功！"];
    }
}

- (PHFetchResult<PHAsset *> *)createdAssets
{
     NSError *error = nil;
    __block NSString *assetID = nil;
    
    // 保存图片到【相机胶卷】
    [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
        assetID = [PHAssetChangeRequest creationRequestForAssetFromImage:self.imageView.image].placeholderForCreatedAsset.localIdentifier;
    } error:&error];
    
    if (error) return nil;
    
    // 获取刚才保存的相片
    return [PHAsset fetchAssetsWithLocalIdentifiers:@[assetID] options:nil];
}

#pragma mark - 获得当前App对应的自定义相册
- (PHAssetCollection *)createdCollection
{
    // 获得软件名字
    NSString *title = [NSBundle mainBundle].infoDictionary[(__bridge NSString *)kCFBundleNameKey];
    
    // 抓取所有的自定义相册
    PHFetchResult<PHAssetCollection *> *collections = [PHAssetCollection fetchAssetCollectionsWithType:PHAssetCollectionTypeAlbum subtype:PHAssetCollectionSubtypeAlbumRegular options:nil];
    
    // 查找当前App对应的自定义相册
    for (PHAssetCollection *collection in collections) {
        if ([collection.localizedTitle isEqualToString:title]) {
            return collection;
        }
    }
    
#pragma mark - 当前App对应的自定义相册没有被创建过 **/
#pragma mark - 创建一个【自定义相册】
    NSError *error = nil;
    __block NSString *createdCollectionID = nil;
    [[PHPhotoLibrary sharedPhotoLibrary] performChangesAndWait:^{
        createdCollectionID = [PHAssetCollectionChangeRequest creationRequestForAssetCollectionWithTitle:title].placeholderForCreatedAssetCollection.localIdentifier;
    } error:&error];
    
    if (error) return nil;
    
    #pragma mark -  根据唯一标识获得刚才创建的相册
    return [PHAssetCollection fetchAssetCollectionsWithLocalIdentifiers:@[createdCollectionID] options:nil].firstObject;
}