Last updated Unknown

App Development **Variable declaration

• var (varname) = (value)

Printing variables

• Put $ before variable

If statements

• when (variable) {

• (condition) → (code)

Unchangeable array = listOf

Changeable array = arrayListOf

Dictionaries = mapOf(key to value)

.getOrDefault

• If can’t get, creates default value

Changeable dictionary = hashMapOf

.put

• Adds key value pair

App Development

Timber

• Used for creating logs in logcat

• Useful for debugging and making sure code runs properly

Lifecycle

• Allows a class to observe and react to the states of another class

To implement:

• Extend the class with LifecycleObserver

• Ask for args upon creation (lifecycle: Lifecycle)

• Add observer to passed lifecycle in constructor (.addObserver(this))

SavedInstanceState

• The function onSavedInstanceState gets called after a program stops

• Used to store different variables you want to keep into a bundle

ex) outState.putInt(intVariable)

• onRestoreInstanceState retrieves the information you put into your variable

• Furthermore, have code that imports savedInstanceState if the bundle isn’t null

App Architecture

UI Controller

• Displaying data, capturing user events

• Should have as little responsibility as possible

• Handles navigation

ViewModel

• Abstract class that survives configuration changes

• Holding data needed for the UI, and preparing it for display

• No size restrictions :o

• Has live data that it sends to ui controller

• Should never reference fragments, activities, or views

Implementation

• Initialize the viewmodel in the UI controller:

ex) private lateinit var viewModel: GameViewModel

• Request viewmodel from ViewModelProviders.of(fragment).get(viewModel::class.java) and store it

• Put this in onCreateView

Factories

• Act as constructors for viewmodel

LiveData

• Observable data holder class that is lifecycle aware

• UI controllers observe the live data

• Will only update ui controllers that are on screen

Implementation

• Turn variable into livedata

//in ui controller onCreate method

• viewModel.score.observe(this, Observer { newScore →

updateScoreText(newScore)

//Score changes

score.value = 1

Encapsulating Live Data

• Create a variable for a mutable live data and then a livedata variable to get the mutable live data

Databases

DAO

Threading

• Processors perform code, and the actions to run code are called threads

• It’s important to not perform long-running operations on the UI thread to prevent blocking and crashing

Coroutines

• Handles long-running tasks efficiently

• Can signal errors with exceptions

• Do the same as callbacks but differ in code

• Asynchronous

• Runs independently from the main execution steps of program

• Non-blocking

• Doesn’t block main ur UI thread

• Instead, it just suspends the thread and does other work until ready

Coroutines need…

• Jobs

• A background job that is cancellable

• Dispatcher

• Sends coroutines to run on various threads

• Scope

• Combines information to define the context in which coroutines run

Implementation

• Create a coroutine in the main thread that runs a suspend function

• Use Dispatchers.IO to call the long-running work**