UI-Testing, Reactive Programming and some Kotlin.

Transcription

1 UI-Testing, Reactive Programming and some Kotlin

2 Load up your guns, and bring your friends This is the end, My only Friend, the end Äntligen stod prästen i predikstolen I ll be back

3 Agenda Questions Recap Testing mostly code Reactive programming Kotlin

4 ReCap

5 5 A GUI for a programmer public void paint(graphics g){ g.moveto(100,100); g.setcolor( ffffff ); g.drawlineto(200,300); } Spans from low level to very high level val intent = Intent() intent.type = "image/*" intent.action = Intent.ACTION_GET_CONTENT startactivityforresult( Intent.createChooser(intent, "Select Picture"), PICK_IMAGE);

6 ...and even visual 6

7 GUI for the User 7

8 8 And GUI for You in this course Java/Android public void paint(graphics g){ g.moveto(100,100); g.setcolor( ffffff ); g.drawlineto(200,300); } Spans from low level to very high level val intent = Intent() intent.type = "image/*" intent.action = Intent.ACTION_GET_CONTENT startactivityforresult( Intent.createChooser(intent, "Select Picture"), PICK_IMAGE);

9 9 How do we get from What user wants and needs (user/system requirements)

10 10 How do we get from public void paint(graphics g){ g.moveto(100,100); g.setcolor( ffffff ); g.drawlineto(200,300); }

11 11 Solution Software_design_pattern Design Patters for gui-code: How to build it Interaction Patterns for user requirements: What to build

12 Testing 12

13 Why Reactive Programming? Why another programming paradigm? Things are different now! Conventional software applications won t be able to fulfill the modern enterprise needs. Its time to rethink about our software architecture patterns and programming techniques.

14 What it actually means to be Reactive? Readily responsive to a stimulus - merriam-webster Reactive Systems : responds in a timely manner stays responsive in the face of failure stays responsive under varying workload rely on asynchronous message-passing

15 Reactive Programming A programming paradigm that helps you to build Reactive Systems. E.g.: Google Spreadsheet In a reactive world, we can't just wait for a function result, a network call, or a database query to return. Every moment we wait for something, we lose the opportunity to do other things in parallel. Reactive programming can be done in several ways Akka Actors Reactive Extensions (Rx) reactive + functional

16 Callbacks A callback is a piece of executable code that is passed as an argument to other code, which is expected to call back the argument at some convenient time.

17 Callbacks Use case : User clicks a button on the Client Client send a request to the Application Application calls service A Get the response from ServiceA and send it to service B Get the response from ServiceB and send it to Service C Get the response from ServiceC and send it to the Client Service A 1 Client Application 2 Service B 3 Service C

18 Callbacks Callback Hell! Callbacks based applications get extremely complex when we have nested callbacks. Leads to messy code, hard to troubleshoot. Example : rxjava/serviceinvoker/callback

19 More the callback hell Unpredictable order In a complex network of listeners, the order in which events are received can depend on the order in which you registered the listeners, which isn t helpful. FRP makes the order in which events are processed not matter by making it completely nondetectable. Missed first event It can be difficult to guarantee that you ve registered your listeners before you send the first event. FRP is transactional, so it s possible to provide this guarantee. Messy state Callbacks push your code into a traditional state-machine style, which gets messy fast. FRP brings order. Leaking callbacks If you forget to deregister your listener, your program will leak memory. Listeners reverse the natural data dependency but don t reverse the keep-alive dependency as you d like them to. FRP does this. Accidental recursion The order in which you update local state and notify listen- ers can be critical, and it s easy to make mistakes. FRP eliminates this issue. Threading issues Attempting to make listeners thread-safe can lead to dead- locks, and it can be difficult to guarantee that no more callbacks will be received after deregistering a listener. FRP eliminates these issues.

20 Paradigm shift Not just a new way of handling callbacks A gentle slide from OOP -> functional

21 Reactive Extensions - Rx ReactiveX is a library for composing asynchronous and event-based programs by using observable sequences. The Observer pattern done right. Initially implemented for C# by Microsoft, later ported to many languages by Netflix Rx. Rx-Java is the Java implementation.

22 Observer Pattern Subject notifies the observers when a change has happened in the subject.

23 Observable Rx-Java introduces Observable data type by extending the traditional Observer Pattern. Observers Observable

24 Observable vs Observer Pattern The producer signal that there is no more data available: the oncompleted() event The producer can signal that an error occurred onerror() event

25 What is functional reactive programming? It s a replacement for the widely used observer pattern, also known as listeners or callbacks. It s a composable, modular way to code event-driven logic. It s a different way of thinking: the program is expressed as a reaction to its inputs, or as a flow of data. It brings order to the management of program state. It s something fundamental: we think that anyone who tries to solve the prob- lems in the observer pattern will eventually invent FRP. It s normally implemented as a lightweight software library in a standard programming language. It can be seen as a complete embedded language for stateful logic.

26 Observable and Subscriber The producer signal that there is no more data available: the subscribe onnext* Subscriber Observable oncompleted

27 Observable and Subscriber In Action

28 Observable and Operators Observable -> Operator -> Subscriber

29 Filtering Observables Selectively emit items from a source Observable

30 Filtering Observables Filtering Operators

31 Transforming Observables Transform items that are emitted by an Observable

32 Transforming Observables Transforming Operators

33 and for Android RxJava is available RxBindings: Android UI-events for RxJava

34 Button b = (Button)findViewById(R.id.button); b.setonclicklistener(new View.OnClickListener() public void onclick(view v) { // Magic } }); Button b = (Button)findViewById(R.id.button); Subscription buttonsub = RxView.clicks(b).subscribe(new Action1<Void>() public void call(void avoid) { // magic stuff } });

35 final EditText name = (EditText) v.findviewbyid(r.id.name); name.addtextchangedlistener(new TextWatcher() public void beforetextchanged(charsequence s, int start, in public void ontextchanged(charsequence s, int start, int be // do some work here with the updated text public void aftertextchanged(editable s) { }); }

36 final EditText name = (EditText) v.findviewbyid(r.id.name); Subscription edittextsub = RxTextView.textChanges(name).subscribe(new Action1<String>() public void call(string value) { //Do what you need to do } });

37 final TextView namelabel = (TextView) findviewbyid(r.id.name final EditText name = (EditText) findviewbyid(r.id.name); Subscription edittextsub = RxTextView.textChanges(name).map(new Func1<CharSequence, String>() public String call(charsequence charsequence) { return new StringBuilder(charSequence).reverse() } }).subscribe(new Action1<String>() public void call(string value) { namelabel.settext(value); } });

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44 Java vs Kotlin Syntax Java final int x; final int y = 1; int w; int z = 2; z = 3; w = 1; Kotlin val x: Int val y = 1 var w: Int var z = 2 z = 3 w = 1 44

45 Is As In Java if(x instanceof Integer){ } final String text = (String) other; if(x >= 0 && x <= 10 ){} Kotlin if (x is Int) { } val text = other as String if (x in 0..10) { } 45

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54 Null Safety Java final String name = null; String lastname; lastname = null Kotlin val name: String? = null var lastname: String? lastname = null var firstname: String firstname = null // Compilation error!! val length = b!!.length 54

55 Model Class in Java 55

56 Model/Data Class in Kotlin 56

57 Let s do some fun :D 57

58 Extensions Feature 58

59 Smart Casting 59

60 More Features 60

61 More Features 61

62 Kotlin Java class MyActivity : AppCompatActivity() { override fun oncreate(savedinstancestate: Bundle?) { super.oncreate(savedinstancestate) setcontentview(r.layout.activity) } } public class MyActivity extends AppCompatActivity protected void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.activity); } }

63 Kotlin Java val fab = findviewbyid(r.id.fab) as FloatingActionButton fab.setonclicklistener {... } FloatingActionButton fab = (FloatingActionButton) findviewbyid(r.id.fab); fab.setonclicklistener(new View.OnClickListener() public void onclick(view view) {... } });

64 Kotlin Java private val monnavigationitemselectedlistener = BottomNavigationView.OnNavigationItemSelectedListener { item -> when (item.itemid) { R.id.navigation_home -> { mtextmessage.settext(r.string.title_home) return@onnavigationitemselectedlistener true } R.id.navigation_dashboard -> { mtextmessage.settext(r.string.title_dashboard) return@onnavigationitemselectedlistener true } } false } private BottomNavigationView.OnNavigationItemSelectedListener monnavigationitemselectedlistener = new BottomNavigationView.OnNavigationItemSelectedListener() public boolean onnavigationitemselected(@nonnull MenuItem item) { switch (item.getitemid()) { case R.id.navigation_home: mtextmessage.settext(r.string.title_home); return true; case R.id.navigation_dashboard: mtextmessage.settext(r.string.title_dashboard); return true; } return false; } };