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Chicago Roboto 2019 notes
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20190425-android-coroutines.md 
suspend fun thing() {
    with (dispatchers.io) {}
}

Dispatchers:

  • Main
  • IO (network/disk)
  • Default (CPU bound)

Good suspend functions are "main safe"

they had literally less ram than i have fingers

Structured concurrency

When a suspend function returns, it has completed all work. launch { } coroutine builder

  • What cancels coroutine work
  • Who gets the exceptions

Scopes keep track of coroutines

val scope = CoroutineScope(Dispatchers.Main)  // MainScope()
scope.launch { ... }

ViewModel.viewModelScope coroutine scope for android viewmodels (in alpha)

launch does not automatically start in the caller's scope, coroutineScope {} builder will do that though.

  • creates child scope of the caller's scope

  • Only resumes after children completes

  • scope returns when child work is complete

  • scope is cancelled when children are cancelled

  • scope is notified when children error

scope.async {} runs outside the scope * withTimeout(n) * mutex.withLock {}

RxCoroutines -> Flow

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20190425-dissecting-stdlib-ii.md

~/Dropbox/RandomlyTyping/...

talks as a giant kotlin file with block comments is cool

operator ad hoc polymorphism 👀

somehow operator fun SomeClass.iterator() makes the class implement Iterable interface???

don't implement both plus() and plusAssign() because of automatic plus-assign sematics with plus() and var references

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20190425-gesture-driven-reddit-app.md

use clip masks instead of changing layout bounds, avoids expensive layout invalidations

recyclerView.isLayoutFrozen = true

Israel Comocho: Smoke & Mirrors 👀

Anything fast enough will look good enough

Collapse animation incorrect Z-ordering (just like it is for fragments)

what is a "Span pool"? 👀

Bitmap rotation turns on bilinear filtering -> jagged edges, add one pixel transparent border (lol)

Keyboard showing:

DecorView
    LinearLayout
        FrameLayout (the one that gets resized)
            LinearLayout
                ActivityContent (android.R.id.content)

use addOnPreDrawListener for activity.window.decorView.viewTreeObserver to animate aandroid.R.id.content size change

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20190425-metaprogramming.md

dagger-reflect 👀 SQLDelight 👀

R class is now generated bytecode instead of java source gen

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20190425-motionlayout-2.0.md
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20190425-navigation.md

navigation-fragment is seperate artifact because google wants to allow use of conductor or other view frameworks

Conditional Navigation

use separate graphs (e.g. a login_graph.xml) global action to navigate to a nested graph from anywhere destination fragment subclass a "SecureFragment":

  • Observe auth status
  • Kick over to login flow graph

YOU CAN POP UP TO A NAV GRAPH DESTINATION OMG

<nav-graph> link in activity registration in manifest expands to intent filters

DO NOT FORGET THIS PART:

// inside activity
override fun onNewIntent(intent: Intent) {
  super.onNewIntent(intent)
  navController.handleDeepLink(intent)
}

Testing Navigation

Fragment scenario build fragment without activity

Custom Destination Types

dialog navigator type 😲

Nav graphs do not live outside the parent activity Graph scoped view model in 2.1.0 alphas

Multi-activity might work well for multi-module * nav controller for in-app navigation * implicitly intents for navigating to features externally * Restrict intents to in app?

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20190426-androidx-test.md

Suggested 70/20/10 split for unit/integration/ui tests

androidx.test can run in JVM outside emulator/device (using robolectric automatically where neccesary?)

  • Junit/Junit androidx extensions testImplementation
  • testInstrumentaitonRunner -> Junit android runnner
  • @RunWith(AndroidJuni4) on test class
  • ApplicationProvider.getApplicationContext<App>()
  • Include robolectric :(
  • test options include android resources = true

Core

val scenario = ActivityScenario.launch(SomeActivity::class.java)
scenario.moveToState(Lifecycle.State.RESUMED)
scenario.recreate()  // destroy and resume with savedInstanceState
scenario.close()
@get:Rule
val activityRule = ActivityScenarioRule(SomeActivity::class.java)
val scenario = activityRule.scenario

Fragment Testing

val scenario = FragmentScenario.launch(SomeFragment::class.java, bundle)
scenario.moveToState(Lifecycle.State.RESUMED)
scenario.onFragment { fragment ->
    //
}

Espresso

  • View matchers
    • ViewMatchers.withId
  • View actions
    • ViewActions.click
  • View assertions
    • ViewAssertions.matches

Recyclerview espresso -> contrib package Intents watching -> contrib

Truth

optional assertions lib

Project Nitrogin 👀

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20190426-engineers-lifecycle.md

What makes mobile special?

  • Focus
  • Intentionality
  • Community
  1. We are all problem solvers

can we better celebrate a long engineering career?

if somebody is happy with the work they are doing, why would you mess with that

  1. priorities and tradeoffs

Sources of burnout

  • culture
    • long hours
    • lots of pressure
  • internal pressure
    • from yourself
  • repetition
    • doing the same thing too long
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20190426-expolayer.md

SimpleExoplayer handles audio sessions automatically :o

Exoplayer is easy enough to use that it should be the default choice for media playback

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20190426-json-explained.md

JSON license: "The software shall be used for Good, not Evil."

-0.0 == 0.0 // true
-0.0.equals(0.0) // false

NaN operators are not reflexive but methods are

JSOM has no NaN or Infinity, but has -0.0

DO NOT use numbers for ids in json, the are treated as floats, which have a much smaller integer range than a Long

java string hashCode sucks, don't rely on it for anything

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20190426-persistence-layer.md

NetworkBoundResource

repository pattern for choosing between network/database retrieval

Reactive queries:

  • Use transactions to commit updates atomically
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20190426-theme-on.md

Anything with layout_ prefix belongs on the view, not in the style - because they are affected by the parent

Text color/size/font goes in a textAppearance style - not relevant to all widgets, just textview subclasses - Text appearances can be used in spans

style affect only the widget the style is applied to, theme applies to all children in the heirarchy

use R.attr references

Theme Inheritance

  • parent="OtherTheme"used as the base, then apply overrides
  • name="Theme.OtherTheme" alternate for declaring inheritance form OtherTheme
  • Set theme in manifest on activity, or by setTheme() BEFORE INFLATING VIEW
val themedContext = ContextThemeWrapper(context, R.style.Theme)
LayoutInflater.from(themedContext)
// or
inflater.cloneInContext(themedCtx)

custom views defStyleAttr Naming: * colorPrimary and onColorPrimary

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20190426-workmanager.md

getRunAttemptCount - Can be used to cancel a task if it fails repeatedly since the framework will just keep retrying it forever.

periodic workers do not return a success state, only enqueued, running.

Periodic tasks have a 15 minute minimum interval

  • workers can be assigned 1..N tags
  • query work by tag
  • NEVER USE cancelAllWork(), it might cancel work from dependencies using workmanager
  • one-time work and periodic work share tags
  • check isStopped() before doing work, worker constraints might not be met
  • cancel all work before removing the workmanager library :D, if it ever gets added back, enqueued tasks that were leftover will start causing crashes because they don't exist anymore.
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