Matthias Käppler, Soundcloud @mttkay
Matt has written his own blog post to accompany his talk.
- this talk is about functional reactive programming
- but without talking about monads or other mathematical terms
- example: a list view with data from the server
- lots of concurrency
- callbacks, broadcast receivers, notifications all over the place
- wanted a single event handling model with natural concurrency
- problem with imperative programming is shared state across whole app
- doesn’t work with multiple threads and concurrency
- programming style should reflect the event-based, network-dependent world that apps live in
- AsyncTask has changed several times in its implementation
- since ICS it uses a single-threaded executor
- prone to leaking Context since you have to manage references yourself
- also has no error handling built-in
- can’t have long-running tasks that depend on each other
- event buses (otto, green robot) also have downsides:
- designed around shared global state
- still no ability to chain tasks
- no built-in error handling
RxJava
- RxJava
- actually a port of .net Rx extensions invented at Microsoft 5 years ago for Windows Phone
- Observable<T> ::onNext(T) ::onCompleted ::onError(Throwable)
- subscribeOn(scheduledThread) / observeOn(scheduledThread)
- have lots of useful schedulers e.g. observer on main Android thread
- also have map and mapMany to compose observables
how to use it
- soundcloud built android extensions
- http://gihub.com/soundcloud/rxjava
- dumb fragments
- service objects implement business objects
- custom operators for paging content in list views etc
- AndroidObservables.fromFragment
- guarantees that it won’t leak but will maintain connection to a rotated activity
e.g.
fetchModels(request) { return fetchResponse(request).mapMany((response) -> { return mapResponse(request, response); }) }simple uniform event model
- unit tests don’t need to run background threads
- apply it in a focussed way
- don’t replace callbacks — used in service layer for API requests
- use proguard!
downsides
- java 6 anonymous classes are very verbose
- deep call stacks in debugging
- slight increase in GC activity (but didn’t have any noticeable performance impact)
- learning curve
- but can use similar things for objective-c and server side (finagle & twitter futures) so can share knowledge
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