Android asynchronous programming
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This document discusses asynchronous programming techniques in Android, including threads and handlers, AsyncTask, and RxAndroid/RxJava. It explains that synchronous calls block the calling thread until the method completes, while asynchronous calls return immediately and execute a callback in a non-blocking way. It provides overviews of threads as units of CPU utilization, handlers for communicating between threads, and AsyncTask for performing background tasks and publishing results on the UI thread. The document also introduces RxJava and RxAndroid for asynchronous programming using observable streams and operators to create, transform, filter, and combine streams.
![AsyncTaskhttps://developer.android.com/reference/android/os/AsyncTask.html
15
When to use? Trigger Triggered From Runs On Limitations /
Drawbacks
- Relatively long
task (UI thread
blocking) with a
need to
communicate with
main thread.[3]
- For tasks in
parallel use
multiple instances
OR Executor [1]
Call to method
execute()
Main Thread Worker thread.
However, Main
thread methods
may be invoked in
between to
publish progress.
- one instance can
only be executed
once (hence
cannot run in a
loop) [2]
- Must be created
and executed from
the Main thread](https://image.slidesharecdn.com/asynchronousprogramming-180423015444/85/Android-asynchronous-programming-15-320.jpg)
Android asynchronous programming
- 2. Asynchronous Programming •Sync & Async •Thread & Handler •AsyncTask •RxAndroid/RxJava 2
- 5. Sync & Async 5 Synchronous call Asynchronous call ● Caller WAITS for method to complete ● Blocking ● Easy to program/understand ● Method returns immediately to caller and executes callback ● Non-blocking ● Run several methods concurrently ● Scalability ● Harder to program
- 7. Thread 7
- 8. Thread 8 What is it? • A basic unit of CPU utilization • Lightweight process • Multiple threads are executed within a process
- 9. Handler 9
- 10. Handler 10 What is it? • Part of the Android system's framework • Communicate between threads: – Send message – Process message
- 11. Handler 11
- 13. AsyncTaskhttps://developer.android.com/reference/android/os/AsyncTask.html What is it? • Helper class around Thread and Handler • Perform background operations • Publish results on the UI thread 13
- 15. AsyncTaskhttps://developer.android.com/reference/android/os/AsyncTask.html 15 When to use? Trigger Triggered From Runs On Limitations / Drawbacks - Relatively long task (UI thread blocking) with a need to communicate with main thread.[3] - For tasks in parallel use multiple instances OR Executor [1] Call to method execute() Main Thread Worker thread. However, Main thread methods may be invoked in between to publish progress. - one instance can only be executed once (hence cannot run in a loop) [2] - Must be created and executed from the Main thread
- 17. RxAndroidhttp://reactivex.io/ 17 ReactiveX is: • A combination of the best ideas from – The Observer pattern – The Iterator pattern – Functional programming • An API for asynchronous programming with observable streams.
- 19. RxAndroidhttps://nhancv.github.io/product/rxjava/ 19 Observable In ReactiveX an observer subscribes to an Observable. • onNext • onError • onCompleted
- 20. RxAndroidhttps://nhancv.github.io/product/rxjava/ 20 Observer • An observer subscribes to an Observable. • An Observable emits items or sends notifications to its observers by calling the observers’ methods.
- 21. RxAndroidhttps://nhancv.github.io/product/rxjava/ 21 PublishSubject • Emits to an observer only those items that are emitted by the source Observable(s) subsequent to the time of the subscription.
- 22. RxAndroidhttps://nhancv.github.io/product/rxjava/ 22 Scheduler • The SubscribeOn operator designates which thread the Observable will begin operating on. • The ObserveOn operator specifies a different Scheduler that the Observable will use to send notifications to its observers. Varieties of Scheduler • Schedulers.computation( ) • Schedulers.io( ) • Schedulers.newThread( )
- 24. RxAndroidhttps://nhancv.github.io/product/rxjava/ 24 Operators Create observable Transforming • create • defer • just • from • map • flat map
- 25. RxAndroidhttp://reactivex.io/ 25 Operators Filtering Combining • debounce • distinct • filter • merge • zip
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