Fast, fluid, instant-gratification apps are a must for mobile and C# async makes this much easier to accomplish. Slides are from the Xamarin CTO and cofounder Miguel de Icaza to understand how and why you should use async for your mobile apps.

1. C# Async on iOS and Android
Miguel de Icaza, CTO
@migueldeicaza

2. C# 5.0 Async on iOS and Android
• Just released our C# 5 compiler
– Async programming
• Support both .NET Base Class Libraries Async
• Async-ready APIs for iOS and Android

3. Asynchronous Programming
Desire to build responsive applications

4. Fluid Uis allows for 60 fps
16m
32ms
64ms

5. Respond to user input

6. Responding to Input
Get events
Dispatch
Update display

7. Get events
Dispatch
Update display

8. C# and Lambdas
• They add a whole level of sanity
• Shared state across lambdas
– Compiler does the heavy lifting
• Requires all lambdas to share a scope

9. Events: Some idioms

10. Perform Long-Running Operations

11. Long-running tasks
• Background threads
• Setup your own
handshake protocol
• Various idioms available

12. Slow file system or database access

13. Network access

14. More callbacks
Get events
Dispatch
Update display

15. Get events
Dispatch
Update display
DB
Net

16. Fluid Uis allows for 60 fps
16m
32ms
64ms

17. Callback Hell

18. Just the other day

19. Callback Hell

20. Problems with callbacks
• Control flow is difficult
– Achieved by choosing what to call next
– Tracking state across callbacks
• Updating code is cumbersome
– Error prone
• Error reporting is bolted on the basic framework
– Poor, and recovery is typically obnoxious, or non-existent

21. Go To Statement Considered Harmful
“our intellectual powers are rather geared to master static
relations and that our powers to visualize processes evolving
in time are relatively poorly developed.
For that reason we should do our utmost to shorten the
conceptual gap between the static program and the dynamic
process, to make the correspondence between the program
(spread out in text space) and the process (spread out in time)
as trivial as possible.” – Edsger W Dijkstra

22. How did we cope with GoTo?
• New idioms
– Structured Programming
• Better languages
– We had the compiler do the work for us

23. Callback Hell

24. C# Async – The Calm after the Storm

25. Evolution: Tasks
• Reasoning about background operations
– Task and Task<T> types
• They encapsulate a unit of work, and have:
– State: running, finished, cancelled
– Result
– Exceptions thrown (if any)

26. Thinking with Tasks
• Many useful operations:
– Wait: Task.WaitAny (t1, t2, t3)
– Wait: Task.WaitAll (t1, t2, t3)
– Chain: task1.ContinueWith (task2);
– Wrap: Task.WhenAny (t1, t2, t3);
– Wrap: Task.WhenAll (t1, t2, t3);

27. Writing beautiful code

28. ShowAlert – creating your own

29. With UIKit Animation

30. Async Support
• Base Class Libraries:
– Expect all the standard Async APIs from .NET BCL
– Coverage is .NET 4.5 Complete for BCL
• More Async Sources:
– Xamarin.iOS: 174
– Xamarin.Android: 337
– Xamarin.Mobile
– Xamarin Component Store

31. What is available as Async?
• Simple Rule:
– Any API that would take more than 50ms to run