Android Development Workshop

This is a workshop that i gave to at the University of Johannesburg in 2018.
In 2019 I did a similar workshop, but the project we built was an API with Ktor.

https://github.com/pjwelcome/Ktor-StarterProject
https://github.com/pjwelcome/AndroidWorkshop

Transcript

1. Android Development Workshop Peter-John Welcome @pjapplez Mobile Engineering Lead
2. Day 1
3. What we will do Today: Intro: 1. Create our first Android app and run it. 2. Git Crash Course 3. Learn Kotlin for Android 4. Crash Course on Android Layouts. (Constraint Layouts) 5. RecyclerViews (View Holder Pattern)
4. Let’s open Android Studio
5. Android Dependencies dependencies { implementation fileTree(dir: 'libs', include: ['*.jar']) implementation"org.jetbrains.kotlin:kotlin-stdlib-jre7:$kotlin_version" implementation 'com.android.support:appcompat-v7:27.1.1' implementation 'com.android.support.constraint:constraint-layout:1.1.2' implementation 'com.android.support:recyclerview-v7:27.1.1' }
6. What is git?
7. What is git? • Git is an example of a DVCS (hence Distributed Version Control System)
8. Kotlin
9. Google announced Kotlin will be an official language for Android
10. Why Kotlin over Java? • Java is very verbose. • Java Code is error prone with all its anonymous inner classes. • Java lacks modern language features. • Nullability issues.
11. Language Features
12. var/val var name : String = "Peter" name = "John" val surname = "Welcome" surname = "Johnson" // val can’t be reassigned
13. Number one reason Android Apps Crash?
14. Null Pointer Exception
15. Nullability var name : String = "Peter" name = null // null can’t be a value on a non-null String var surname : String? = "Peter" surname = null val otherName = surname ?: "" // Elvis operator ( ?? in other languages)
16. Classes
17. Classes class User { private val name: String private val surname : String constructor(name : String , surname: String) { this .name = name this.surname = surname } } var user = User( surname = "Welcome", name = "Peter") // named arguments
18. Data class @Parcelize data class Human (private var name: String, val age: Int) : Parcelable //copy, equal, hashcode, toString var human = Human("Peter",27)
19. Sealed Classes sealed class Result<out T>{ data class Success<out T> (val value : T) : Result<T>() data class Error(val error : MyError) : Result<MyError>() }
20. Sealed Classes fun <T>resultsFromService(result : Result<T>) : String { when (result) { is Result.Success -> "${result.value} World" is Result.Error -> return result.error.toString() } return "" } resultsFromService(Result.Success("Hello"))
21. Functions
22. First class citizens
23. High order functions
24. Functions fun hello(){ print("Hello") } val functionAsVariable = hello() val greetingPeter = fun (func : (name :String) -> String ) : String = func("Peter") greetingPeter { "Hello $it" }
25. Extension functions
26. Extension functions infix fun Int.add (value : Int) = this + value val result = 1.add(1) val result = 1 add 1 //Extension function fun <T> Observable<T>.applySchedulers() : Observable<T> = this.subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread()) //Usage disposable.add(this.viewModel.createPlant(Plant(name = "Best Plant Ever")).applySchedulers().subscribe ())
27. Function Literals with Receiver
28. Function Literals with Receiver inline fun SharedPreferences.edit(action: SharedPreferences.Editor.() -> Unit) { val editor = edit() editor.action() editor.apply() } getSharedPreferences("cache", Context.MODE_PRIVATE).edit { putString("username", "Peter") }
29. Async Programming
30. AsyncTasks class doAsyncTask(textView: TextView) : AsyncTask<Unit, Unit, String>() { val innerTextView: TextView? = textView override fun doInBackground(vararg params: Unit?): String? { try { ... return data } catch (e: Exception) { return null } } override fun onPostExecute(result: String?) { super.onPostExecute(result) innerTextView?.text = JSONObject(result).toString() } }
31. AsyncTasks
32. RxJava disposable.add(viewModel.fetchDashboardPlants() .applySchedulers() .subscribe({ //onNext: ... }, { error -> //onError }) ) fun <T> Observable<T>.applySchedulers() : Observable<T> = this.subscribeOn(Schedulers.io()).observeOn(AndroidSchedulers.mainThread())
33. Coroutines internal val background = newFixedThreadPoolContext(2, "background") launch (background) { val result = resultsFromService(Result.Success("Hello")) launch(UI) { this.textView.text = result } } // The async await way val someLongRunningTask = async<String>(CommonPool) { return@async "" }.await()
34. Let’s build our app.
35. Life Cycles and Resources
36. Layouts (Constraint Layout)
37. RecyclerView
38. RecyclerView <?xml version="1.0" encoding="utf-8"?> <android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" > <android.support.v7.widget.RecyclerView android:id="@+id/rv_item_repo" android:layout_width="match_parent" android:layout_height="match_parent" /> </android.support.constraint.ConstraintLayout>
39. RecyclerView <android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent"> <TextView android:id="@+id/tv_animal_type" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginStart="8dp" android:layout_marginTop="48dp" android:layout_marginEnd="16dp" android:text="animal name" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent" /> </android.support.constraint.ConstraintLayout>
40. RecyclerView class AnimalAdapter(val items: ArrayList<String>) : RecyclerView.Adapter<ViewHolder>() { // Gets the number of animals in the list override fun getItemCount(): Int { return items.size } // Inflates the item views override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder { return ViewHolder(LayoutInflater.from(parent.context).inflate(R.layout.animal_list_item, parent, false)) } // Binds each animal in the ArrayList to a view override fun onBindViewHolder(holder: ViewHolder, position: Int) { holder.tvAnimalType.text = items.get(position) } } class ViewHolder(view: View) : RecyclerView.ViewHolder(view) { // Holds the TextView that will add each animal to val tvAnimalType = view.tv_animal_type }
41. Slides https://tinyurl.com/ycb3cn7f Workshop Feedback https://bit.ly/2uFagmK