This project was initially implemented by me while doing a code quiz at one interesting IT company. It was intended to be a simple two view app with a collection view of avatars shown in the first view and a table view depicting all image downloads happening in the second view. The list of requirements for the avatar view included:
- activity indicator should be shown in the cell while the avatar download is in progress
- when avatar download is completed the image should be set for the image view and activity indicator should be dismissed
- if the download fail the cell should simply have gray background without activity indicator
The second view, which was supposed to provide the status and progress of each download initiated in the first view had to fulfill these requirements:
- the cell should contain the title of the avatar
- the cell should indicate the status of the assigned downlod (queued, in progress, done or failed)
- the cell should show the progress of the download
- the cell should depict the timestamp of the last modification of the download status
The main rule of that code quiz was to implement all image downloading and caching without the use of third-party libraries and caching needed to be done only in the main memory without writting the images to disk.
The final project was also required to have some unit or/and integration tests implemented. Thus, for the coding I was allowed to use any library and approach I prefer as well as the language: Obj-C or Swift.
As I've been digging into the world of FRP and specifically the RxSwift library for a while, I have considered it to be a great candidate to apply here that would simplify a lot of asynchronous stuff.
For the actual download of the images a URLSession and it's URLSessionDownloadTask were utilized. This way it was possible to track the download progress of the task and report it to the user with a progress indicator. Again, in any other project I would with high probability consider using the Alamofire, which even got the rx wrapper already written.
According to requirements caching had to be organized only in the main memory resulting. The two possible solutions that came to my mind were to use the URLCache that could be set at the time of session init and the second one, more interesting way - by using RxSwift shareReplay operator on task observer. ShareReplay operator would allow me to get the latest event from the observable on subscription even upon completion. URLCache approach however was much more flexible and allowed to persist the requests to disk if needed by simply changing its config. At the time when I was doing the code quiz due either to the lack of time and the pressure of the approaching submit deadline (I had aproximately 4 hours) or for some other mysterious reason I have sticked to the first approach. Now after a nice amount of the refactoring the BehaviorSubject does the job for me, even though the URLCache is hooked-up too.
The data provider for this project was the adorable avatar API. The service provides avatars placeholder for web developers and designers and is easy to use due to the lack of any authorization/authentication. You can simply send a request with the avatar id in the url and it will provide you with the image.
| Avatars view | Downloads view |
|---|---|
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