The document is a postmortem by Frank A. Krueger discussing the development of the Mocast podcast player, highlighting both successes and failures encountered during the project. Key achievements include effective UI design and reliance on bindings for data updates, while significant challenges arose from an inadequate 'episode class' structure and limitations with iCloud syncing. The postmortem emphasizes lessons learned to improve future projects, particularly the need for better data modeling and practices in asynchronous programming.

1. Mocast Postmortem
Frank A. Krueger
Seattle Mobile .NET
July 1, 2014

2. What’s a Postmortem?
After a project finishes in a big production for a
movie, video game, or large project. Everyone
gets together to discuss in a meeting what went
wrong and what could be done better. The
issues brought up are almost always completely
ignored by management and they continue to
make the same incompetent mistakes they always
have.
- Urban Dictionary

3. What’s a Mocast?
• Podcast player
• Thumb-friendly UI
• Emphasizes the full catalog
• ADD-friendly UI

4. What Went Right?
!
What Went Wrong?

5. Right: UI Design
Goal: Make it iOS 7-y

6. Right: UI Design
Goal: Make it iOS 7-y
Goal: Non-modal
(no Now Playing screen, no Episode screen)

7. Right: UI Design

8. Right: UI Design

9. Right: UI Design

11. Right: UI Design

12. Right: Reliance on Bindings
INotifyCollectionChanged
INotifyPropertyChanged

13. Right: Reliance on Bindings
• Producers:
• ObservableCollection
• ObservableQuery!
• Consumers:
• ObservableTableView

14. Right: Reliance on Bindings
• A query that changes over time and
depends on other collections and
queries
• Emits minimal CollectionChanged events
• Automatic Update Throttling
• General Purpose - you put anything into
the “query”

16. Right: iCloud Syncing
• Mocast uses iCloud Key-Value store
• Very simple API, very simple update model

17. Right: iCloud Syncing

18. Right: Async Everywhere
• Async is the greatest thing to happen to UI
development since Visual Basic
!
announceTask = AnnounceNewEpisodeAsync (episode, streaming);
!
beginSeeking = true;
beginSeekingPosition = GetPlaybackPosition (ue);
await BeginSeekingAsync ();
if (announceTask != null) {
await announceTask;
announceTask = null;
}
player.Rate = BaseRate;
!
UpdatePositionData ();
UpdatePlaybackInfo ();

19. Wrong

20. Wrong: The “Episode Class”
• Oh my, I don’t have an Episode class!
• Instead, 3 classes comprise “Episode” based upon the source of
data:
• UserEpisode has all the data a user can control (play
position, tags, etc.) and is sync’d with iCloud
• DataEpisode has all the info from the podcast feed
• DownloadEpisode has information regarding its download
status
• Each implements IEpisodeReference so they can be correlated

21. Wrong: The “Episode Class”
Doesn’t Work :-(

22. Wrong: The “Episode Class”

23. Wrong: The “Episode Class”
I allowed the data source API
to dictate my domain model :-(

24. Wrong: The “Episode Class”
The Fix

25. Wrong: The “Episode Class”
The Fix

26. Wrong: Threaded
ObservableQueries
• To do modern UI programming, you need to do as
much / all work asynchronously
• My ObservableQuery started, naïvely, as thread-
dumb
• Eventually, had to make the class itself thread-safe
but did not require thread-safe queries so
couldn’t automatically run them on separate threads
• Result: UI freezes under very heavy load

27. Wrong: Threaded
ObservableQueries
The Fix
Instead of:
!
ObservableQuery (Func<T> source)!
!
I should have:
!
ObservableQuery (Func<Task<T>> asyncSource)

28. Wrong: iCloud Sync
• Wonderful because it’s simple
• BUT very small storage size:
• 1,000 keys
• 1 MB data

29. Wrong: iCloud Sync
• Use CloudKit!
The Fix

30. Wrong: Manual Entity Binding

31. Wrong: Manual Entity Binding
The Fix
?

32. Wrong: Manual Entity Binding
The Fix
There just aren’t many good declarative data binders out
there:
!
My Bind Library
That Reactive Library
MvvmCross
BindableObject / Dependency Properties (haha)

33. • Require re-architecting around their pattern
• Make for great demos, but have real-world issues:
• async
• reference cleanup
• throttling
• deep hierarchies
• greedy events
• …
Wrong: Manual Entity Binding

34. Thank you!
• Mocast will be available
on iPhone/iPod in a
couple weeks