Creating airplane mode proof (Xamarin) applications
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Slides for my talk at Expert Day for Xamarin 2018 --- It has never been more important to create apps that also work offline. Mobile app users can flick that 'airplane mode' switch any given time and the cellular connection isn't as stable as it is at home. To ensure a great user-experience you, as a developer, need to account for these scenarios. And honestly: that can be a pain in the butt. In this session I will show you how to use awesome libraries like Akavache and Polly to create connected apps in a very easy way. Step-by-step I will guide you through a sample application, so when we're done you can go home and implement it in your every app. Have a good flight!
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Creating airplane mode proof (Xamarin) applications
- 1. Creating airplane mode proof (Xamarin) applications Gerald Versluis HELLO Xamarin Experts!
- 3. “Our app doesn’t even have to be fast, it’s enough that the user thinks it is fast” @jfversluis
- 4. Layers of Mobile Development Thousands of iOS and Android APIs Public web APIs Backend integrations Third party libraries Memory,CPU and network constraints @jfversluis
- 5. Network constraints • Mobile connection not always stable • Bandwidth costs money • Network calls take time @jfversluis
- 6. @jfversluis Image source: https://imgur.com/gallery/JQEWkBy The eight fallacies https://en.wikipedia.org/wiki/Fallacies_of_distributed_computing 1. The network is reliable. 2. Latency is zero. 3. Bandwidth is infinite. 4. The network is secure. 5. Topology doesn't change. 6. There is one administrator. 7. Transport cost is zero. 8. The network is homogeneous.
- 7. What Options Do We Have? • Emulator/Simulator have options to mimic network conditions • Network Link Conditioner (iOS) https://developer.apple.com/download/more/? q=Additional%20Tools • Or on your physical device 👉 • Built into the Android Emulator (Stock/Genymotion) @jfversluis
- 8. What Options Do We Have? • Monitoring tool to see what is going over the line (or, you know over the air..) • Charles (Windows/Mac/Linux) • Fiddler (Windows/Mac (Mono)) • Wireshark (Windows/Mac) (if you like pain) • HTTPScoop (Mac) @jfversluis
- 10. @jfversluis All code can be found on: Image source: http://getwallpapers.com/collection/matrix-code-wallpaper-hd https://github.com/jfversluis/ AirplaneModeProof
- 11. @jfversluis Version 1.0 The basics Image source: https://www.themarysue.com/avengers-age-of-ultron-easter-eggs/
- 12. Avengers Assemble! https://github.com/jfversluis/AirplaneModeProof • Sample App • Access information about each member • See in which comics they appear • Xamarin.Forms & ASP.NET Core backend (on Azure) @jfversluis
- 13. @jfversluis Version 2.0 Quick Wins! Image source: http://knowyourmeme.com/memes/success-kid-i-hate-sandcastles
- 14. FFImageLoading https://github.com/luberda-molinet/FFImageLoading • Fast & Furious Image Loading • Can cache images in-memory and on disk • Deduplication of similar download/ load requests • Retry image downloads @jfversluis
- 15. FFImageLoading https://github.com/luberda-molinet/FFImageLoading • Has more awesome features: • Transformations • SVG / WebP / GIF support • Loading and error placeholders • Don’t forget Init();! @jfversluis
- 16. Connectivity Plugin https://github.com/jamesmontemagno/ConnectivityPlugin • Check connection status • Information about connection type, bandwidth, etc. • Has methods to see if a certain host is reachable • Has events to catch changes in state @jfversluis
- 17. Refit https://github.com/paulcbetts/refit • No more duplicate code to do REST calls 🎉 • Implement the contract as an interface • Calls will be generated at compile time • Not just for Xamarin! @jfversluis
- 18. @jfversluis Version 3.0 Adding Akavaching Image source: http://www.douglasequipment.com/hand-trucks/heavy-duty-warehouse-trucks-miami/
- 19. Implement Caching the Hard Way Image source: https://codemilltech.com/akavache-is-aka-awesome/
- 20. Akavache https://github.com/akavache/Akavache • “Asynchronous, persistent key-value store based on SQLite3” • Caching is important • Network resiliency • Perceived app performance • Not just for Xamarin! @jfversluis
- 21. Akavache: Lessons Learned https://github.com/akavache/Akavache • Add the Akavache.SQLite3 package and make sure you have the AkavacheSqliteLinkerOverride.cs file included • Shut down properly with: BlobCache.Shutdown().Wait(); • On mobile a bit hard because of the lifecycle • Wrap in a repository pattern • Alternative: Monkey Cache by James Montemagno @jfversluis
- 22. @jfversluis Version 4.0 Join the Resilience Image source: https://mmoexaminer.com/star-wars-needs-mmorpg-thats-official-canon/
- 23. Polly https://github.com/App-vNext/Polly • “.NET resilience and transient-fault-handling library” • Defining policies for failed requests • More info: http://www.thepollyproject.org/ • Not just for Xamarin! @jfversluis
- 24. Polly @jfversluis Source: https://github.com/App-vNext/Polly/blob/master/README.md Policy Premise Aka Mitigation Retry Many faults are transient and may self-correct after a short delay. "Maybe it's just a blip" Allows configuring automatic retries. Circuit-breaker When a system is seriously struggling, failing fast is better than making users/callers wait. Protecting a faulting system from overload can help it recover. "Stop doing it if it hurts" or “Give that system a break” Breaks the circuit (blocks executions) for a period, when faults exceed some pre-configured Timeout Beyond a certain wait, a success result is unlikely. "Don't wait forever" Guarantees the caller won't have to wait beyond the timeout. Fallback Things will still fail - plan what you will do when that happens. "Degrade gracefully" Defines alternative value to be returned (or action to be executed) on failure.
- 25. @jfversluis Version 5.0 HTTP Conditional Requests Image source: https://mmoexaminer.com/star-wars-needs-mmorpg-thats-official-canon/
- 26. HTTP Conditional Requests https://developer.mozilla.org/en-US/docs/Web/HTTP/Conditional_requests • “HTTP conditional requests are requests that are executed differently, depending on the value of specific headers.” • Only returns data if something changed • If-Match, If-None-Match, If-Modified-Since, If-Modified- Since and If-Range • Most common use-case is caching @jfversluis
- 27. Take-aways • Write less redundant code with Refit • Keep in mind the limitations of a mobile device • Give the user the perception of speedy loading • More optimizations possible with If-None-Match and/of If- Modified-Since @jfversluis Heads-up! Get your camera out to take pictures of the resources links on the next slide
- 28. Resources • https://robgibbens.com/resilient-network-services-with- xamarin/ • https://codemilltech.com/akavache-is-aka-awesome/ • https://xamgirl.com/consuming-a-restful-web-service-in- xamarin-forms-using-refit-part-1/ • https://xamarinhelp.com/resilient-network-connectivity- xamarin-forms/ @jfversluis