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.

1. @MOLSJEROEN GETTING THE MOST OUT OF ANDROID KTX
2. @MOLSJEROEN
3. @MOLSJEROEN WHAT AND WHY CRASH COURSE WRITE YOUR OWN DISCOVER MORE
4. WHAT AND WHY
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() } })
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() } })
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() } })
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() } })
9. @MOLSJEROEN KTX TO THE RESCUE view.doOnLayout { doOnWidthAndHeightKnown() }
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) } } }
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) } } }
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) } } }
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) } } }
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) } }) }
15. @MOLSJEROEN WHAT IS KTX
16. @MOLSJEROEN WHAT IS KTX
17. @MOLSJEROEN WHAT IS KTX
18. @MOLSJEROEN HOW TO USE KTX repositories { google() } dependencies { implementation "androidx.core:core:1.2.0" }
19. @MOLSJEROEN HOW TO USE KTX repositories { google() } dependencies { implementation "androidx.core:core:1.2.0" }
20. @MOLSJEROEN HOW TO USE KTX repositories { google() } dependencies { implementation “androidx.core:core-ktx:1.2.0” }
21. CRASH COURSE
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!!) })
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) }
24. @MOLSJEROEN ANIMATIONS val animator = ObjectAnimator.ofFloat(view, View.ALPHA, 0f, 1f) animator.doOnPause { doSomething(it) } animator.doOnResume { doSomething(it) }
25. @MOLSJEROEN SYSTEM SERVICES // requires android M val layoutInflater = context .getSystemService(LayoutInflater::class.java)
26. @MOLSJEROEN SYSTEM SERVICES // requires android M val layoutInflater = context .getSystemService(LayoutInflater::class.java) // any Android version context.getSystemService<LayoutInflater>()
27. @MOLSJEROEN SHAREDPREFERENCES sharedPrefs.edit().putBoolean("key", true).apply()
28. @MOLSJEROEN SHAREDPREFERENCES sharedPrefs.edit().putBoolean("key", true).apply() sharedPrefs.edit { putBoolean("key", true) } sharedPrefs.edit(commit = true) { putBoolean("key", true) }
29. @MOLSJEROEN COLORS val red = Color.parseColor("#ff0000") val colorDrawable = ColorDrawable(red)
30. @MOLSJEROEN COLORS val red = Color.parseColor("#ff0000") val colorDrawable = ColorDrawable(red) val red = "#ff0000".toColorInt() val colorDrawable = red.toDrawable()
31. @MOLSJEROEN URI AND FILE val uri = “https://jeroenmols.com/blog”.toUri() val file = uri.toFile() val fileUri = file.toUri()
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
33. @MOLSJEROEN VIEW view.updateLayoutParams<ConstraintLayout.LayoutParams> { width = 200 // strong typed access height = 200 } view.updatePadding(right = 10) // only assign one val bitmap = view.drawToBitmap()
34. @MOLSJEROEN VIEW VISIBILITY if (view.visibility == View.VISIBLE) { // do something } view.visibility = View.VISIBLE
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
36. @MOLSJEROEN VIEWGROUP viewGroup.contains(view) viewGroup.forEach { } viewGroup.isEmpty() viewGroup.isNotEmpty() viewGroup += view viewGroup -= view
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() })
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() }
39. @MOLSJEROEN VIEWMODELS - ACTIVITY // scoped to activity val viewmodel = ViewModelProviders.of(this) .get(MyViewModel::class.java)
40. @MOLSJEROEN VIEWMODELS - ACTIVITY // scoped to activity val viewmodel = ViewModelProviders.of(this) .get(MyViewModel::class.java) // scoped to activity val viewModel by viewModels<MyViewModel>()
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)
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<MyViewModel>() // scoped to activity val activityViewModel by activityViewModels<MyViewModel>()
43. @MOLSJEROEN VIEWMODELS - FACTORY val viewModel = ViewModelProviders.of(this, VModelFactory()) .get(MyViewModel::class.java)
44. @MOLSJEROEN VIEWMODELS - FACTORY val viewModel = ViewModelProviders.of(this, VModelFactory()) .get(MyViewModel::class.java) val viewModel by viewModels<MyViewModel>() { VModelFactory() }
45. @MOLSJEROEN FRAGMENT TRANSACTIONS fragmentManager.beginTransaction() .replace(R.id.container, Fragment()).commit()
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()) }
47. @MOLSJEROEN COROUTINE SCOPES AppCompatActivity().lifecycleScope.launch { } Fragment().lifecycleScope.launch { } ViewModel().viewModelScope.launch { }
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
49. WRITE YOUR OWN
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,$numDecimals})?)||(\\.)?" .toRegex() if (regex.matches(result)) null else "" } } editText.limitDecimalsTo(2)
51. @MOLSJEROEN LIMIT DECIMALS IN EDITTEXT fun EditText.limitDecimalsTo(numDecimals: Int) { filters += InputFilter { s, start, end, d, dstart, dend -> val newText = s.subSequence(start, end).toString() val result = StringBuilder(d) .replace(dstart, dend, newText).toString() val regex = “[0-9]*((\\.[0-9]{0,$numDecimals})?)||(\\.)?" .toRegex() if (regex.matches(result)) null else "" } } editText.limitDecimalsTo(2)
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,$numDecimals})?)||(\\.)?" .toRegex() if (regex.matches(result)) null else "" } } editText.limitDecimalsTo(2)
53. @MOLSJEROEN TOAST fun Fragment.toast(@StringRes message: Int) = Toast.makeText(context, message, LENGTH_SHORT).show() fun Fragment.toast(message: String) = Toast.makeText(context, message, LENGTH_SHORT).show() toast(R.id.mymessage) toast("Hello there")
54. @MOLSJEROEN TOAST fun Fragment.toast(@StringRes message: Int) = Toast.makeText(context, message, LENGTH_SHORT).show() fun Fragment.toast(message: String) = Toast.makeText(context, message, LENGTH_SHORT).show() toast(R.id.mymessage) toast("Hello there")
55. @MOLSJEROEN FLOAT fun Float.isDecimalNumber() = this % 1 > 0.0001 fun Float.decimalsOrRound(digits: Int) = if (isDecimalNumber()) { String.format("%.${digits}f", this) } else { String.format("%.0f", this) } 12.3f.isDecimalNumber() 12.3001f.decimalsOrRound(2)
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)
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() }
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() }
59. DISCOVER MORE
60. @MOLSJEROEN LEARN MORE ABOUT KTX bit.ly/ktx-docs bit.ly/ktx-extensions bit.ly/ktx-source
61. WRAP UP
62. @MOLSJEROEN IDIOMATIC CODE SIMPLIFY DEVELOPMENT REDUCE ERRORS WRITE YOUR OWN GET INSPIRED
63. @MOLSJEROEN HTTPS://JEROENMOLS.COM/BLOG
64. @MOLSJEROEN IMAGE CREDITS Welcome image by Clement127 https://flic.kr/p/QdpUY8 Official Android and Google logo's Font awesome https://fontawesome.com/
65. MOLSJEROEN