I'm kind of new to programming in general, so I have this maybe simple question. Actually, writing helps me to identify the problem faster.

Anyway, I have an app with multiple asynchronous calls, they are nested like this:

```
InstagramUnoficialAPI.shared.getUserId(from: username, success: { (userId) in

    InstagramUnoficialAPI.shared.fetchRecentMedia(from: userId, success: { (data) in

        InstagramUnoficialAPI.shared.parseMediaJSON(from: data, success: { (media) in

                guard let items = media.items else { return }
                self.sortMediaToCategories(media: items, success: {

                    print("success")

          // Error Handlers

```

Looks horrible, but that's not the point. I will investigate the Promise Kit once I get this working. 

I need the `sortMediaToCategories` to wait for completion and then reload my collection view. However, in the `sortMediaToCategories` I have another nested function, which is async too and has a for in loop. 

```
func sortMediaToCategories(media items: [StoryData.Items],
                           success: @escaping (() -> Swift.Void),
                           failure: @escaping (() -> Swift.Void)) {

    let group = DispatchGroup()
    group.enter()

    for item in items {

        if item.media_type == 1 {

            guard let url = URL(string: (item.image_versions2?.candidates?.first!.url)!) else {return}

            mediaToStorageDistribution(withImageUrl: url,
                                       videoUrl: nil,
                                       mediaType: .jpg,
                                       takenAt: item.taken_at,
                                       success: { group.notify(queue: .global(), execute: {

                                        self.collectionView.reloadData()
                                           group.leave()

                                       })  },
                                       failure: { print("error") })

 //....

```

I can't afford the collection view to reload every time obviously, so I need to wait for loop to finish and then reload. 

I'm trying to use Dispatch Groups, but struggling with it. Could you please help me with this? Any simple examples and any advice will be very appreciated.