Getting the most out of Android KTX

Video: https://www.youtube.com/watch?v=B8ei4rHAHEA

Ever wish you could just use a lambda as an onClickListener? Or change the View visibility by modifying a simple "isVisible" boolean? Or how about using a doOnLayout{} method to run a block of code after view layout?

These are just a few examples of how Android KTX extensions help solve common problems. They improve the existing Jetpack and Android platform APIs so you can consume them from Kotlin in a concise and idiomatic way.

This talk will discuss what KTX extensions are and explore the most useful extensions that you can use in your daily workflow.

Transcript

1. @MOLSJEROEN
   GETTING THE MOST
   OUT OF ANDROID KTX
   

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2. @MOLSJEROEN
   

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3. @MOLSJEROEN
   WHAT AND WHY
   CRASH COURSE
   WRITE YOUR OWN
   DISCOVER MORE
   

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4. WHAT AND WHY
   

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5. @MOLSJEROEN
   ANDROID CAN SOMETIMES BE TEDIOUS
   view.addOnLayoutChangeListener(
   object : View.OnLayoutChangeListener {
   override fun onLayoutChange(
   view: View,
   left: Int, top: Int,
   right: Int, bottom: Int,
   oldLeft: Int, oldTop: Int,
   oldRight: Int, oldBottom: Int) {
   view.removeOnLayoutChangeListener(this)
   doOnWidthAndHeightKnown()
   }
   })
   

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6. @MOLSJEROEN
   ANDROID CAN SOMETIMES BE TEDIOUS
   view.addOnLayoutChangeListener(
   object : View.OnLayoutChangeListener {
   override fun onLayoutChange(
   view: View,
   left: Int, top: Int,
   right: Int, bottom: Int,
   oldLeft: Int, oldTop: Int,
   oldRight: Int, oldBottom: Int) {
   view.removeOnLayoutChangeListener(this)
   doOnWidthAndHeightKnown()
   }
   })
   

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7. @MOLSJEROEN
   ANDROID CAN SOMETIMES BE TEDIOUS
   view.addOnLayoutChangeListener(
   object : View.OnLayoutChangeListener {
   override fun onLayoutChange(
   view: View,
   left: Int, top: Int,
   right: Int, bottom: Int,
   oldLeft: Int, oldTop: Int,
   oldRight: Int, oldBottom: Int) {
   view.removeOnLayoutChangeListener(this)
   doOnWidthAndHeightKnown()
   }
   })
   

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8. @MOLSJEROEN
   ANDROID CAN SOMETIMES BE TEDIOUS
   view.addOnLayoutChangeListener(
   object : View.OnLayoutChangeListener {
   override fun onLayoutChange(
   view: View,
   left: Int, top: Int,
   right: Int, bottom: Int,
   oldLeft: Int, oldTop: Int,
   oldRight: Int, oldBottom: Int) {
   view.removeOnLayoutChangeListener(this)
   doOnWidthAndHeightKnown()
   }
   })
   

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9. @MOLSJEROEN
   KTX TO THE RESCUE
   view.doOnLayout { doOnWidthAndHeightKnown() }
   

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10. @MOLSJEROEN
    KTX UNDER THE HOOD
    inline fun View.doOnLayout(
    crossinline action: (view: View) -> Unit
    ) {
    if (ViewCompat.isLaidOut(this) && !isLayoutRequested) {
    action(this)
    } else {
    doOnNextLayout {
    action(it)
    }
    }
    }
    

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11. @MOLSJEROEN
    KTX UNDER THE HOOD
    inline fun View.doOnLayout(
    crossinline action: (view: View) -> Unit
    ) {
    if (ViewCompat.isLaidOut(this) && !isLayoutRequested) {
    action(this)
    } else {
    doOnNextLayout {
    action(it)
    }
    }
    }
    

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12. @MOLSJEROEN
    KTX UNDER THE HOOD
    inline fun View.doOnLayout(
    crossinline action: (view: View) -> Unit
    ) {
    if (ViewCompat.isLaidOut(this) && !isLayoutRequested) {
    action(this)
    } else {
    doOnNextLayout {
    action(it)
    }
    }
    }
    

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13. @MOLSJEROEN
    KTX UNDER THE HOOD
    inline fun View.doOnLayout(
    crossinline action: (view: View) -> Unit
    ) {
    if (ViewCompat.isLaidOut(this) && !isLayoutRequested) {
    action(this)
    } else {
    doOnNextLayout {
    action(it)
    }
    }
    }
    

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14. @MOLSJEROEN
    KTX UNDER THE HOOD
    inline fun View.doOnNextLayout(
    crossinline action: (view: View) -> Unit
    ) {
    addOnLayoutChangeListener(object : View.OnLayoutChangeListener {
    override fun onLayoutChange(
    view: View,
    left: Int, top: Int, right: Int, bottom: Int,
    oldLeft: Int, oldTop: Int, oldRight: Int, oldBottom: Int
    ) {
    view.removeOnLayoutChangeListener(this)
    action(view)
    }
    })
    }
    

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15. @MOLSJEROEN
    WHAT IS KTX
    

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16. @MOLSJEROEN
    WHAT IS KTX
    

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17. @MOLSJEROEN
    WHAT IS KTX
    

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18. @MOLSJEROEN
    HOW TO USE KTX
    repositories {
    google()
    }
    dependencies {
    implementation "androidx.core:core:1.2.0"
    }
    

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19. @MOLSJEROEN
    HOW TO USE KTX
    repositories {
    google()
    }
    dependencies {
    implementation "androidx.core:core:1.2.0"
    }
    

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20. @MOLSJEROEN
    HOW TO USE KTX
    repositories {
    google()
    }
    dependencies {
    implementation “androidx.core:core-ktx:1.2.0”
    }
    

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21. CRASH COURSE
    

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22. @MOLSJEROEN
    ANIMATIONS
    animator.addListener(object : Animator.AnimatorListener {
    override fun onAnimationStart(animation: Animator?) =
    doSomething(animation!!)
    override fun onAnimationRepeat(animation: Animator?) =
    doSomething(animation!!)
    override fun onAnimationEnd(animation: Animator?) =
    doSomething(animation!!)
    override fun onAnimationCancel(animation: Animator?) =
    doSomething(animation!!)
    })
    

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23. @MOLSJEROEN
    ANIMATIONS
    val animator = ObjectAnimator.ofFloat(view, ALPHA, 0f, 1f)
    animator.doOnStart { doSomething(it) }
    animator.doOnRepeat { doSomething(it) }
    animator.doOnCancel { doSomething(it) }
    animator.doOnEnd { doSomething(it) }
    

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24. @MOLSJEROEN
    ANIMATIONS
    val animator = ObjectAnimator.ofFloat(view, View.ALPHA, 0f, 1f)
    animator.doOnPause { doSomething(it) }
    animator.doOnResume { doSomething(it) }
    

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25. @MOLSJEROEN
    SYSTEM SERVICES
    // requires android M
    val layoutInflater = context
    .getSystemService(LayoutInflater::class.java)
    

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26. @MOLSJEROEN
    SYSTEM SERVICES
    // requires android M
    val layoutInflater = context
    .getSystemService(LayoutInflater::class.java)
    // any Android version
    context.getSystemService()
    

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27. @MOLSJEROEN
    SHAREDPREFERENCES
    sharedPrefs.edit().putBoolean("key", true).apply()
    

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28. @MOLSJEROEN
    SHAREDPREFERENCES
    sharedPrefs.edit().putBoolean("key", true).apply()
    sharedPrefs.edit { putBoolean("key", true) }
    sharedPrefs.edit(commit = true) { putBoolean("key", true) }
    

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29. @MOLSJEROEN
    COLORS
    val red = Color.parseColor("#ff0000")
    val colorDrawable = ColorDrawable(red)
    

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30. @MOLSJEROEN
    COLORS
    val red = Color.parseColor("#ff0000")
    val colorDrawable = ColorDrawable(red)
    val red = "#ff0000".toColorInt()
    val colorDrawable = red.toDrawable()
    

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31. @MOLSJEROEN
    URI AND FILE
    val uri = “https://jeroenmols.com/blog”.toUri()
    val file = uri.toFile()
    val fileUri = file.toUri()
    

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32. @MOLSJEROEN
    VIEW
    view.doOnLayout { }
    view.doOnNextLayout { }
    view.doOnPreDraw { }
    view.doOnAttach { }
    view.doOnDetach { }
    view.marginStart
    view.marginEnd
    view.marginLeft
    view.marginRight
    view.marginTop
    view.marginBottom
    

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33. @MOLSJEROEN
    VIEW
    view.updateLayoutParams {
    width = 200 // strong typed access
    height = 200
    }
    view.updatePadding(right = 10) // only assign one
    val bitmap = view.drawToBitmap()
    

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34. @MOLSJEROEN
    VIEW VISIBILITY
    if (view.visibility == View.VISIBLE) {
    // do something
    }
    view.visibility = View.VISIBLE
    

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35. @MOLSJEROEN
    VIEW VISIBILITY
    if (view.visibility == View.VISIBLE) {
    // do something
    }
    view.visibility = View.VISIBLE
    if (view.isVisible) {
    // do something
    }
    view.isVisible = false // View.GONE
    

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36. @MOLSJEROEN
    VIEWGROUP
    viewGroup.contains(view)
    viewGroup.forEach { }
    viewGroup.isEmpty()
    viewGroup.isNotEmpty()
    viewGroup += view
    viewGroup -= view
    

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37. @MOLSJEROEN
    TEXTVIEW
    editText.addTextChangedListener(object : TextWatcher {
    override fun afterTextChanged(s: Editable?) =
    doWork()
    override fun beforeTextChanged(s: CharSequence?, start: Int,…) =
    doWork()
    override fun onTextChanged(s: CharSequence?, start: Int,…) =
    doWork()
    })
    

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38. @MOLSJEROEN
    TEXTVIEW
    editText.addTextChangedListener(object : TextWatcher {
    override fun afterTextChanged(s: Editable?) =
    doWork()
    override fun beforeTextChanged(s: CharSequence?, start: Int,…) =
    doWork()
    override fun onTextChanged(s: CharSequence?, start: Int,…) =
    doWork()
    })
    editText.doOnTextChanged { text, start, count, after -> doWork() }
    editText.doAfterTextChanged { doWork() }
    editText.doBeforeTextChanged { text, start, count, after -> doWork() }
    

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39. @MOLSJEROEN
    VIEWMODELS - ACTIVITY
    // scoped to activity
    val viewmodel = ViewModelProviders.of(this)
    .get(MyViewModel::class.java)
    

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40. @MOLSJEROEN
    VIEWMODELS - ACTIVITY
    // scoped to activity
    val viewmodel = ViewModelProviders.of(this)
    .get(MyViewModel::class.java)
    // scoped to activity
    val viewModel by viewModels()
    

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41. @MOLSJEROEN
    VIEWMODELS - FRAGMENT
    // scoped to fragment
    val viewModel = ViewModelProviders.of(this)
    .get(MyViewModel::class.java)
    // scoped to activity
    val viewModel = ViewModelProviders.of(requireActivity())
    .get(MyViewModel::class.java)
    

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42. @MOLSJEROEN
    VIEWMODELS - FRAGMENT
    // scoped to fragment
    val viewModel = ViewModelProviders.of(this)
    .get(MyViewModel::class.java)
    // scoped to activity
    val viewModel = ViewModelProviders.of(requireActivity())
    .get(MyViewModel::class.java)
    // scoped to fragment
    val viewModel by viewModels()
    // scoped to activity
    val activityViewModel by activityViewModels()
    

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43. @MOLSJEROEN
    VIEWMODELS - FACTORY
    val viewModel = ViewModelProviders.of(this, VModelFactory())
    .get(MyViewModel::class.java)
    

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44. @MOLSJEROEN
    VIEWMODELS - FACTORY
    val viewModel = ViewModelProviders.of(this, VModelFactory())
    .get(MyViewModel::class.java)
    val viewModel by viewModels() { VModelFactory() }
    

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45. @MOLSJEROEN
    FRAGMENT TRANSACTIONS
    fragmentManager.beginTransaction()
    .replace(R.id.container, Fragment()).commit()
    

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46. @MOLSJEROEN
    FRAGMENT TRANSACTIONS
    fragmentManager.beginTransaction()
    .replace(R.id.container, Fragment()).commit()
    fragmentManager.commit { replace(R.id.container, Fragment()) }
    fragmentManager.commit(allowStateLoss = true)
    { replace(R.id.container, Fragment()) }
    

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47. @MOLSJEROEN
    COROUTINE SCOPES
    AppCompatActivity().lifecycleScope.launch { }
    Fragment().lifecycleScope.launch { }
    ViewModel().viewModelScope.launch { }
    

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48. @MOLSJEROEN
    AND MANY MORE
    Benchmark
    Graphics
    Spannable
    SparseArrays
    Ranges
    Menu
    Lifecycle
    Livedata & flow
    Navigation
    Paging
    Preferences
    Room
    Slices
    Sqlite
    Workmanager
    Playcore
    …
    bit.ly/ktx-extensions
    

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49. WRITE YOUR OWN
    

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50. @MOLSJEROEN
    LIMIT DECIMALS IN EDITTEXT
    fun EditText.limitDecimalsTo(numDecimals: Int) {
    filters += InputFilter { s, start, end, d, dstart, dend ->
    val newText = s.subSequence(start, end).toString()
    val result = StringBuilder(d)
    .replace(dstart, dend, newText).toString()
    val regex = “[0-9]*((\\.[0-9]{0,$numDecimals})?)||(\\.)?"
    .toRegex()
    if (regex.matches(result)) null else ""
    }
    }
    editText.limitDecimalsTo(2)
    

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51. @MOLSJEROEN
    LIMIT DECIMALS IN EDITTEXT
    fun EditText.limitDecimalsTo(numDecimals: Int) {
    filters += InputFilter { s, start, end, d, dstart, dend ->
    val newText = s.subSequence(start, end).toString()
    val result = StringBuilder(d)
    .replace(dstart, dend, newText).toString()
    val regex = “[0-9]*((\\.[0-9]{0,$numDecimals})?)||(\\.)?"
    .toRegex()
    if (regex.matches(result)) null else ""
    }
    }
    editText.limitDecimalsTo(2)
    

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52. @MOLSJEROEN
    LIMIT DECIMALS IN EDITTEXT
    fun EditText.limitDecimalsTo(numDecimals: Int) {
    filters += InputFilter { s, start, end, d, dstart, dend ->
    val newText = s.subSequence(start, end).toString()
    val result = StringBuilder(d)
    .replace(dstart, dend, newText).toString()
    val regex = “[0-9]*((\\.[0-9]{0,$numDecimals})?)||(\\.)?"
    .toRegex()
    if (regex.matches(result)) null else ""
    }
    }
    editText.limitDecimalsTo(2)
    

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53. @MOLSJEROEN
    TOAST
    fun Fragment.toast(@StringRes message: Int) =
    Toast.makeText(context, message, LENGTH_SHORT).show()
    fun Fragment.toast(message: String) =
    Toast.makeText(context, message, LENGTH_SHORT).show()
    toast(R.id.mymessage)
    toast("Hello there")
    

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54. @MOLSJEROEN
    TOAST
    fun Fragment.toast(@StringRes message: Int) =
    Toast.makeText(context, message, LENGTH_SHORT).show()
    fun Fragment.toast(message: String) =
    Toast.makeText(context, message, LENGTH_SHORT).show()
    toast(R.id.mymessage)
    toast("Hello there")
    

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55. @MOLSJEROEN
    FLOAT
    fun Float.isDecimalNumber() = this % 1 > 0.0001
    fun Float.decimalsOrRound(digits: Int) =
    if (isDecimalNumber()) {
    String.format("%.${digits}f", this)
    } else {
    String.format("%.0f", this)
    }
    12.3f.isDecimalNumber()
    12.3001f.decimalsOrRound(2)
    

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56. @MOLSJEROEN
    FLOAT
    fun Float.isDecimalNumber() = this % 1 > 0.0001
    fun Float.decimalsOrRound(digits: Int) =
    if (isDecimalNumber()) {
    String.format("%.${digits}f", this)
    } else {
    String.format("%.0f", this)
    }
    12.3f.isDecimalNumber()
    12.3001f.decimalsOrRound(2)
    

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57. @MOLSJEROEN
    TABSELECTED LISTENER
    fun TabLayout.doOnTabSelected(listener: (text: String) -> Unit) {
    clearOnTabSelectedListeners()
    addOnTabSelectedListener(object : TabLayout.OnTabSelectedListener {
    override fun onTabReselected(tab: TabLayout.Tab?) = Unit
    override fun onTabUnselected(tab: TabLayout.Tab?) = Unit
    override fun onTabSelected(tab: TabLayout.Tab?) =
    listener.invoke(tab!!.text.toString())
    })
    }
    tabLayout.doOnTabSelected { doSomething() }
    

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58. @MOLSJEROEN
    TABSELECTED LISTENER
    fun TabLayout.doOnTabSelected(listener: (text: String) -> Unit) {
    clearOnTabSelectedListeners()
    addOnTabSelectedListener(object : TabLayout.OnTabSelectedListener {
    override fun onTabReselected(tab: TabLayout.Tab?) = Unit
    override fun onTabUnselected(tab: TabLayout.Tab?) = Unit
    override fun onTabSelected(tab: TabLayout.Tab?) =
    listener.invoke(tab!!.text.toString())
    })
    }
    tabLayout.doOnTabSelected { doSomething() }
    

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59. DISCOVER MORE
    

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60. @MOLSJEROEN
    LEARN MORE ABOUT KTX
    bit.ly/ktx-docs
    bit.ly/ktx-extensions
    bit.ly/ktx-source
    

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61. WRAP UP
    

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62. @MOLSJEROEN
    IDIOMATIC CODE
    SIMPLIFY DEVELOPMENT
    REDUCE ERRORS
    WRITE YOUR OWN
    GET INSPIRED
    

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63. @MOLSJEROEN
    HTTPS://JEROENMOLS.COM/BLOG
    

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64. @MOLSJEROEN
    IMAGE CREDITS
    Welcome image by Clement127
    https://flic.kr/p/QdpUY8
    Official Android and Google logo's
    Font awesome
    https://fontawesome.com/
    

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65. MOLSJEROEN
    

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