Crashing is good for your app

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In the name of God Crashing is good for your app

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I am Seyed Jafari Software Engineer @ Revolut Ltd worldsnas.com @worldsnas

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What is a CRASH 💥 Wiki: In computing, a crash, occurs when a software application stops functioning properly and exits. Me: When a program stops working unexpectedly

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How do they crash? 🤔 ● Hardware issues ● Galactic rays 🤯 ● Software bugs

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Software bugs Exceptions

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Exception Techopedia: An exception is an abnormal or unprecedented event that occurs after the execution of a software program or application. It is a runtime error of an undesired result or event aﬀecting normal program ﬂow.

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Exceptions for exceptionals! When something terribly goes wrong. It’s unacceptable. No way! Does not meet the rules. Simple Example: var result = 1 / 0

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Famous exceptions/errors we all know 1. NullPointerException 2. IOException 3. OutOfMemoryError 4. StackOverﬂowError Kotlin/Native InvalidMutabilityException

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Exceptions Good Bad or

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Exception driven vs If-Else Eﬀective Java chapter 10, item 69 Elixir

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Use Cases and how to deal with them

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fun getBookNames(libraryId : String): Data> = try { Data.Success(fetchBookNames(libraryId)) }catch(e : IOException) { Data.Failed(e) } NetworkRequests AwesomeRepository.kt Catching example

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Enum mappings Good Exceptions enum class LightSwitchState{ ON, OFF, UNKNOWN, } fun mapStateToEnum(state : String): LightSwitchState = LightSwitchState .values() .find { it.name == state } ?: UNKNOWN

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Enum mappings Good Exceptions enum class LightSwitchState{ ON, OFF, } fun mapStateToEnum(state : String): LightSwitchState? = LightSwitchState .values() .find { it.name == state }

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Enum mappings Good Exceptions enum class LightSwitchState{ ON, OFF, } fun mapStateToEnum(state : String): LightSwitchState = LightSwitchState .values() .first { it.name == state }

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var binding: FragmentAwesomeBinding? = null ViewBinding vs Fragments AwesomeFragment.kt Good Exceptions fun setTitle(txt : String) { binding?.title.text = txt }

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var _binding: FragmentAwesomeBinding? = null val binding get() = _binding!! fun onViewCreated(view: View) { _binding = FragmentAwesomeBinding.bind(view) } fun onViewDestroyed(view: View){ _binding = null } fun setTitle(txt : String) { binding.title.text = txt } ViewBinding vs Fragments AwesomeFragment.kt Good Exceptions

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Good Exceptions var _binding: FragmentAwesomeBinding? = null val binding get() = _binding!! fun onViewCreated(view: View) { _binding = FragmentAwesomeBinding.bind(view) } fun onViewDestroyed(view: View){ _binding = null } fun setTitle(txt : String) { binding.title.text = txt } ViewBinding vs Fragments AwesomeFragment.kt

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Good Exceptions Business logics and specs fun packThreeBooks(books : List): BookPack { require(books.size == 3){ "we need exactly three books to pack" } return packageBooks(books) }

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Catching exceptions Safe layering the good exceptions fun getBooksAndPackThem(library : Library) : BookPack? { val books = library.getBooks() return try{ packThreeBooks(books) }catch(e: Exception){ null } }

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Try-catch Let them pass vs

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BUT

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Exception vs UX

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Exception is bad for UX, Let’s Fix it 1. Try-Catch everything 2. Add Safe Layers 3. Set Thread Uncaught Exception handlers We are safe now!

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Are we really “safe“ now?

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UX in “Safe” mode fun enablePayBtn() { binding?.payBtn.isEnabled = true } Users: Still not ﬁxed

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Let it crash fun enablePayBtn() { binding.payBtn.isEnabled = true } Users: Fixed immediately

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Still not convinced? 😲 Another example...

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I hear you, skepticals! Logging

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Exception Logging vs

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I/Fitness: OnPackageChangedOperation got intent: Intent... I/Icing: Indexing com.google.android.gms-apps from com.google.android.gms [CONTEXT service_id=21 ] I/Icing: Indexing done com.google.android.gms-apps [CONTEXT service_id=21 ] I/Telecom: DefaultDialerCache: Refreshing default dialer for user 0: now com.android.dialer: DDC.oR@AI8 I/system_server: Background young concurrent copying GC freed 80900(4601KB) AllocSpace objects, 11(1124KB) LOS objects, 11% free, 31MB/35MB, paused 458us total 142.940ms I/CarrierSvcBindHelper: No carrier app for: 0 I/Fitness: FitCleanupIntentOperation received Intent android.intent.action.PACKAGE_CHANGED I/Fitness: OnPackageChangedOperation got intent: Intent... I/Icing: Indexing com.google.android.gms-apps from com.google.android.gms [CONTEXT service_id=21 ] I/Icing: Indexing done com.google.android.gms-apps [CONTEXT service_id=21 ] I/Fitness: FitCleanupIntentOperation received Intent android.intent.action.PACKAGE_CHANGED Logging issues Dear Logcat indistinct

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java.lang.OutOfMemoryError at android.graphics.BitmapFactory.nativeDecodeAsset(Native Method) at android.graphics.BitmapFactory.decodeStream(BitmapFactory.java:683) at android.graphics.BitmapFactory.decodeResourceStream(BitmapFactory.java:513) at android.graphics.drawable.Drawable.createFromResourceStream(Drawable.java:889) at android.content.res.Resources.loadDrawable(Resources.java:3436) at android.content.res.Resources.getDrawable(Resources.java:1909) at android.view.View.setBackgroundResource(View.java:16251) at com.autkusoytas.bilbakalim.SoruEkrani.cevapSecimi(SoruEkrani.java:666) at com.autkusoytas.bilbakalim.SoruEkrani$9$1.run(SoruEkrani.java:862) at android.os.Handler.handleCallback(Handler.java:733) ….. Exceptions advantage Dear Logcat Easily distinguishable

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● V: Verbose. ● D: Debug. ● I: Info. ● W: Warning. ● E: Error. ● A: Assert. Logging issues Android SDK Hard to choose

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Exceptions advantage Java std throwables Clear types ● java.lang.NullPointerException ● java.io.IOException ● java.lang.IllegalStateException ● java.lang.IllegalArgumentException ● java.lang.OutOfMemoryError ● java.lang.StackOverflowError

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tag= MainActivity::class.simpleName, msg= "some f… thing went wrong", tr= null Logging issues Logcat.d Manual INFO gathering ) Log.d(

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Exceptions advantage IllegalArgumentException() Automatic Info attaching ● No tags needed ● StackTrace ● Name is a good enough message

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● Checking logs regularly (usually ignored) ● Finding the right one (find a needle in a haystack) ● Setting severity level ● Assigning to the right team ● Velocity Alerts Logging issues Slow & Hard Addersing

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Exceptions advantage Fast & Easy Addersing ● They are highly prioritised (fixed even during weekends! 󰣻) ● Usually delivered to devs inbox ● They can be assigned automatically ● Types can be used as Severity ● Alerts already set (Crashlytics)

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● Firebase Events Logging issues Custom vs Paid options Reporting tool

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Exceptions advantage Exception reporting services Most of the services are free ● Crashlytics ● Sentry ● Yandex ● Bugsnag

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Logs Are good and useful Not a replacement for Exceptions

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Exceptions Good Bad or It depends

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💥 Happy Crashing 💥 @worldsnas Reach out to me about your crashes 🤗 Thanks We are actively hiring in wide range of positions. make sure to checkout our openings on: https://www.revolut.com/careers