Android Puzzlers: Traps, Pitfalls and Corner Cases

Android is a marvellous platform that has been evolving for more than 10 years. Having such a large framework, so many methods and classes while maintaining legacy generally ends up with a price to pay: some parts of the SDK comes with their questions and puzzlers.

In this talk, we will present some of the most head-scratching API namings/usages/results and give an explanation for each of them.

Transcript

1. Android Puzzlers Traps, Pitfalls and Corner Cases @cyrilmottier ? ? ? ? ? ? ? ? ?
2. It all began with…
4. Small applications with curious behavior Android puzzlers
5. Small applications with curious behavior Android puzzlers 1. What does it print?
6. Small applications with curious behavior Android puzzlers 1. What does it print? 2. The solution revealed
7. Small applications with curious behavior Android puzzlers 1. What does it print? 2. The solution revealed 3. The moral
8. A simple setup apply plugin: 'kotlin-android' apply plugin: 'kotlin-android-extensions' android { compileSdkVersion 28 defaultConfig { minSdkVersion 28 targetSdkVersion 28 versionCode 1 versionName "1.0" } buildTypes { release { minifyEnabled false proguardFiles getDefaultProguardFile('proguard-android-optimize.txt') } } } dependencies { implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:1.3.21" } common.gradle
9. <?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" package="com.cyrilmottier.android.puzzlers" tools:ignore="AllowBackup,GoogleAppIndexingWarning"> <application android:allowBackup=“false" android:label=“@string/app_name“ android:supportsRtl="true" android:theme="@style/android:Theme.Material.Light.DarkActionBar"> <activity android:name=".MainActivity"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> </manifest> A simple setup AndroidManifest.xml
10. A simple setup minSdkVersion 28 targetSdkVersion 28 compileSdkVersion 28 Running on Android 9 (Pie) / API 28 Warnings/errors/lint turned off Focusing on vanilla-Android
11. Inflation result
12. <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:tag="child" /> MainActivity.kt layout/view_inflate.xml class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val parent = FrameLayout(this).apply { tag = "parent" } val result1 = layoutInflater.inflate(R.layout.view_inflate, parent) val result2 = layoutInflater.inflate(R.layout.view_inflate, null) trace("${result1.tag} and ${result2.tag}") } }
13. <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:tag="child" /> MainActivity.kt layout/view_inflate.xml class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val parent = FrameLayout(this).apply { tag = "parent" } val result1 = layoutInflater.inflate(R.layout.view_inflate, parent) val result2 = layoutInflater.inflate(R.layout.view_inflate, null) trace("${result1.tag} and ${result2.tag}") } }
14. A child and child class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val parent = FrameLayout(this).apply { tag = "parent" } val result1 = layoutInflater.inflate(R.layout.view_inflate, parent) val result2 = layoutInflater.inflate(R.layout.view_inflate, null) trace("${result1.tag} and ${result2.tag}") } } <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:tag="child" /> MainActivity.kt layout/view_inflate.xml
15. B parent and child A child and child class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val parent = FrameLayout(this).apply { tag = "parent" } val result1 = layoutInflater.inflate(R.layout.view_inflate, parent) val result2 = layoutInflater.inflate(R.layout.view_inflate, null) trace("${result1.tag} and ${result2.tag}") } } <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:tag="child" /> MainActivity.kt layout/view_inflate.xml
16. B parent and child C throws NullPointerException A child and child class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val parent = FrameLayout(this).apply { tag = "parent" } val result1 = layoutInflater.inflate(R.layout.view_inflate, parent) val result2 = layoutInflater.inflate(R.layout.view_inflate, null) trace("${result1.tag} and ${result2.tag}") } } <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:tag="child" /> MainActivity.kt layout/view_inflate.xml
17. B parent and child C throws NullPointerException D Answer D A child and child class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val parent = FrameLayout(this).apply { tag = "parent" } val result1 = layoutInflater.inflate(R.layout.view_inflate, parent) val result2 = layoutInflater.inflate(R.layout.view_inflate, null) trace("${result1.tag} and ${result2.tag}") } } <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:tag="child" /> MainActivity.kt layout/view_inflate.xml
18. B parent and child C throws NullPointerException D Answer D A child and child class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val parent = FrameLayout(this).apply { tag = "parent" } val result1 = layoutInflater.inflate(R.layout.view_inflate, parent) val result2 = layoutInflater.inflate(R.layout.view_inflate, null) trace("${result1.tag} and ${result2.tag}") } } <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:tag="child" /> MainActivity.kt layout/view_inflate.xml
19. attaches child to parent & returns parent null null parent parent returns child root returns child attaches child to parent & returns parent Output
20. Favor the 3-args inflate method instead fun LayoutInflater.inflate( resource: Int, root: ViewGroup, attachToRoot: Boolean ): View Be explicit
21. null null parent parent false true false true returns child root attachToRoot returns child returns child attaches child to parent & returns parent Output
22. null null parent parent false true false true returns child root attachToRoot returns child returns child attaches child to parent & returns parent Output
23. Padding precedence
24. MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) trace( "start=${text.paddingStart} top=${text.paddingTop} " + "end=${text.paddingEnd} bottom=${text.paddingBottom}" ) } }
25. MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) trace( "start=${text.paddingStart} top=${text.paddingTop} " + "end=${text.paddingEnd} bottom=${text.paddingBottom}" ) } } <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/text" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/padded_rect" android:padding="5px" android:paddingBottom="6px" android:paddingEnd="7px" android:paddingHorizontal="8px" android:paddingLeft="9px" android:paddingRight="10px" android:paddingStart="11px"/> layout/activity_main.xml
26. MainActivity.kt <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/text" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/padded_rect" android:padding="5px" android:paddingBottom="6px" android:paddingEnd="7px" android:paddingHorizontal="8px" android:paddingLeft="9px" android:paddingRight="10px" android:paddingStart="11px"/> <?xml version="1.0" encoding="utf-8"?> <shape xmlns:android="http://schemas.android.com/apk/res/android"> <padding android:bottom="1px" android:left="2px" android:right="3px" android:top="4px" /> </shape> layout/activity_main.xml drawable/padded_rect.xml class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) trace( "start=${text.paddingStart} top=${text.paddingTop} " + "end=${text.paddingEnd} bottom=${text.paddingBottom}" ) } }
27. class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) trace( "start=${text.paddingStart} top=${text.paddingTop} " + "end=${text.paddingEnd} bottom=${text.paddingBottom}" ) } } B start=9 top=5 end=10 bottom=6 C start=2 top=4 end=3 bottom=1 D start=11 top=5 end=7 bottom=5 A start=5 top=5 end=5 bottom=5 MainActivity.kt <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/text" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/padded_rect" android:padding="5px" android:paddingBottom="6px" android:paddingEnd="7px" android:paddingHorizontal="8px" android:paddingLeft="9px" android:paddingRight="10px" android:paddingStart="11px"/> layout/activity_main.xml drawable/padded_rect.xml <?xml version="1.0" encoding="utf-8"?> <shape xmlns:android="http://schemas.android.com/apk/res/android"> <padding android:bottom="1px" android:left="2px" android:right="3px" android:top="4px" /> </shape>
28. <?xml version="1.0" encoding="utf-8"?> <shape xmlns:android="http://schemas.android.com/apk/res/android"> <padding android:bottom="1px" android:left="2px" android:right="3px" android:top="4px" /> </shape> B start=9 top=5 end=10 bottom=6 C start=2 top=4 end=3 bottom=1 D start=11 top=5 end=7 bottom=5 A start=5 top=5 end=5 bottom=5 MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) trace( "start=${text.paddingStart} top=${text.paddingTop} " + "end=${text.paddingEnd} bottom=${text.paddingBottom}" ) } } <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/text" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@drawable/padded_rect" android:padding="5px" android:paddingBottom="6px" android:paddingEnd="7px" android:paddingHorizontal="8px" android:paddingLeft="9px" android:paddingRight="10px" android:paddingStart="11px"/> layout/activity_main.xml drawable/padded_rect.xml
29. background Drawable padding supportsRtl = false Lower Lower Higher
30. background Drawable padding padding[Start|End] Lower Lower Higher supportsRtl = false
31. background Drawable padding padding[Start|End] Lower Lower Higher padding[Left|Top|Right|Bottom] supportsRtl = false
32. padding[Left|Top|Right|Bottom] padding[Horizontal|Vertical] background Drawable padding padding[Start|End] Lower Lower Higher supportsRtl = false
33. padding[Left|Top|Right|Bottom] padding[Horizontal|Vertical] padding background Drawable padding padding[Start|End] Lower Lower Higher supportsRtl = false
34. padding[Left|Top|Right|Bottom] padding[Horizontal|Vertical] padding background Drawable padding padding[Start|End] padding[Left|Top|Right|Bottom] padding[Horizontal|Vertical] padding padding[Start|End] background Drawable padding supportsRtl = true Lower Higher supportsRtl = false
35. Activity lifecycle
36. MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) trace("onCreate") finish() trace("finish") } override fun onStart() { super.onStart() trace("onStart") } override fun onResume() { super.onResume() trace("onResume") } override fun onPause() { trace("onPause") super.onPause() } override fun onStop() { trace("onStop") super.onStop() } override fun onDestroy() { trace("onDestroy") super.onDestroy() } }
37. B onCreate, finish, onStart, onResume, onPause, onStop, onDestroy C onCreate, onStart, onResume, onPause, onStop, onDestroy D onCreate, finish, onDestroy A onCreate MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) trace("onCreate") finish() trace("finish") } override fun onStart() { super.onStart() trace("onStart") } override fun onResume() { super.onResume() trace("onResume") } override fun onPause() { trace("onPause") super.onPause() } override fun onStop() { trace("onStop") super.onStop() } override fun onDestroy() { trace("onDestroy") super.onDestroy() } }
38. B onCreate, finish, onStart, onResume, onPause, onStop, onDestroy C onCreate, onStart, onResume, onPause, onStop, onDestroy D onCreate, finish, onDestroy A onCreate MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) trace("onCreate") finish() trace("finish") } override fun onStart() { super.onStart() trace("onStart") } override fun onResume() { super.onResume() trace("onResume") } override fun onPause() { trace("onPause") super.onPause() } override fun onStop() { trace("onStop") super.onStop() } override fun onDestroy() { trace("onDestroy") super.onDestroy() } }
40. “The following diagram shows the important state paths of an Activity. – d.android.com
41. “The following diagram shows the important state paths of an Activity. – d.android.com
42. Drawable tags
43. MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val classNames = arrayOf( R.drawable.level_list, R.drawable.layer_list, R.drawable.shape ).map { getDrawable(it)::class.java.simpleName } trace(classNames.joinToString(", ")) } }
44. MainActivity.kt drawable/level_list.xml <?xml version="1.0" encoding="utf-8"?> <level-list /> class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val classNames = arrayOf( R.drawable.level_list, R.drawable.layer_list, R.drawable.shape ).map { getDrawable(it)::class.java.simpleName } trace(classNames.joinToString(", ")) } }
45. MainActivity.kt drawable/level_list.xml <?xml version="1.0" encoding="utf-8"?> <level-list /> drawable/layer_list.xml <?xml version="1.0" encoding="utf-8"?> <layer-list /> class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val classNames = arrayOf( R.drawable.level_list, R.drawable.layer_list, R.drawable.shape ).map { getDrawable(it)::class.java.simpleName } trace(classNames.joinToString(", ")) } }
46. MainActivity.kt drawable/level_list.xml <?xml version="1.0" encoding="utf-8"?> <level-list /> drawable/layer_list.xml <?xml version="1.0" encoding="utf-8"?> <layer-list /> drawable/shape.xml <?xml version="1.0" encoding="utf-8"?> <shape /> class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val classNames = arrayOf( R.drawable.level_list, R.drawable.layer_list, R.drawable.shape ).map { getDrawable(it)::class.java.simpleName } trace(classNames.joinToString(", ")) } }
47. B LevelDrawable, LayerListDrawable, ShapeDrawable C LevelListDrawable, LayerDrawable, GradientDrawable D throws InflateException A LevelListDrawable, LayerListDrawable, ShapeDrawable MainActivity.kt drawable/level_list.xml <?xml version="1.0" encoding="utf-8"?> <level-list /> drawable/layer_list.xml <?xml version="1.0" encoding="utf-8"?> <layer-list /> drawable/shape.xml <?xml version="1.0" encoding="utf-8"?> <shape /> class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val classNames = arrayOf( R.drawable.level_list, R.drawable.layer_list, R.drawable.shape ).map { getDrawable(it)::class.java.simpleName } trace(classNames.joinToString(", ")) } }
48. B LevelDrawable, LayerListDrawable, ShapeDrawable C LevelListDrawable, LayerDrawable, GradientDrawable D throws InflateException A LevelListDrawable, LayerListDrawable, ShapeDrawable MainActivity.kt drawable/level_list.xml <?xml version="1.0" encoding="utf-8"?> <level-list /> drawable/layer_list.xml <?xml version="1.0" encoding="utf-8"?> <layer-list /> drawable/shape.xml <?xml version="1.0" encoding="utf-8"?> <shape /> class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val classNames = arrayOf( R.drawable.level_list, R.drawable.layer_list, R.drawable.shape ).map { getDrawable(it)::class.java.simpleName } trace(classNames.joinToString(", ")) } }
49. The general rule <valar-morghulis /> ValarMorghulisDrawable
50. The general rule
51. The general rule <level-list /> <transition /> <ripple /> <adaptive-icon /> <color /> <vector /> <animated-vector /> <scale /> <clip /> <rotate /> <inset /> <bitmap /> <nine-patch /> LevelListDrawable TransitionDrawable RippleDrawable AdaptiveIconDrawable ColorDrawable VectorDrawable AnimatedVectorDrawable ScaleDrawable ClipDrawable RotateDrawable InsetDrawable BitmapDrawable NinePatchDrawable <animated-image /> AnimatedImageDrawable xceptions
52. Exceptions The general rule
53. Exceptions <selector /> <animated-selector /> <layer-list /> <animation-list /> <shape /> StateListDrawable AnimatedStateListDrawable LayerDrawable AnimationDrawable GradientDrawable
54. Exceptions <selector /> <animated-selector /> <layer-list /> <animation-list /> <shape /> StateListDrawable AnimatedStateListDrawable LayerDrawable AnimationDrawable GradientDrawable ShapeDrawable PaintDrawable PictureDrawable
55. Exceptions <selector /> <animated-selector /> <layer-list /> <animation-list /> <shape /> <animated-rotate /> StateListDrawable AnimatedStateListDrawable LayerDrawable AnimationDrawable GradientDrawable ShapeDrawable PaintDrawable PictureDrawable
56. Exceptions <selector /> <animated-selector /> <layer-list /> <animation-list /> <shape /> <animated-rotate /> <com.cyrilmottier.YourDrawable /> StateListDrawable AnimatedStateListDrawable LayerDrawable AnimationDrawable GradientDrawable ShapeDrawable PaintDrawable PictureDrawable YourDrawable
57. Fragment lifecycle
58. TracingFragment.kt class TracingFragment : Fragment() { override fun onAttach(context: Context?) { super.onAttach(context) trace("onAttach") } override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) trace("onCreate") } override fun onCreateView( inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle? ): View? { trace("onCreateView") return super.onCreateView(inflater, container, savedInstanceState) } override fun onDestroyView() { trace("onDestroyView") super.onDestroyView() } override fun onDestroy() { trace("onDestroy") super.onDestroy() } override fun onDetach() { trace("onDetach") super.onDetach() } }
59. MainActivity.kt class MainActivity : FragmentActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val fragment = TracingFragment() supportFragmentManager.beginTransaction() .add(android.R.id.content, fragment, "fragment:puzzler") .commit() supportFragmentManager.beginTransaction() .detach(fragment) .commit() } override fun onSaveInstanceState(outState: Bundle?) { // For the simplicity of this puzzler, // let’s consider state is never ever saved } }
60. B onAttach, onCreate, onCreateView, onDestroyView C onCreate, onDestroy D Nothing A onAttach, onCreate, onCreateView, onDestroyView, onDestroy, onDetach MainActivity.kt class MainActivity : FragmentActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val fragment = TracingFragment() supportFragmentManager.beginTransaction() .add(android.R.id.content, fragment, "fragment:puzzler") .commit() supportFragmentManager.beginTransaction() .detach(fragment) .commit() } override fun onSaveInstanceState(outState: Bundle?) { // For the simplicity of this puzzler, // let’s consider state is never ever saved } }
61. B onAttach, onCreate, onCreateView, onDestroyView C onCreate, onDestroy D Nothing A onAttach, onCreate, onCreateView, onDestroyView, onDestroy, onDetach MainActivity.kt class MainActivity : FragmentActivity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val fragment = TracingFragment() supportFragmentManager.beginTransaction() .add(android.R.id.content, fragment, "fragment:puzzler") .commit() supportFragmentManager.beginTransaction() .detach(fragment) .commit() } override fun onSaveInstanceState(outState: Bundle?) { // For the simplicity of this puzzler, // let’s consider state is never ever saved } }
62. add remove/replace attach/detach the Fragment and more… creates/destroys the Fragment’s associated View turns Fragment’s View visibility to GONE/VISIBLE Fragment actions attach detach show hide FragmentTransaction commands
63. Notification channels
64. MainActivity.kt private const val CHANNEL_ID = "channel" class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val manager = getSystemService(NotificationManager::class.java) val aChannel = NotificationChannel( CHANNEL_ID, // id "A name", // name NotificationManager.IMPORTANCE_DEFAULT // importance (3) ) aChannel.lightColor = Color.RED manager.createNotificationChannel(aChannel) manager.deleteNotificationChannel(CHANNEL_ID) val anotherChannel = NotificationChannel( CHANNEL_ID, // id "Another name", // name NotificationManager.IMPORTANCE_HIGH // importance (4) ) anotherChannel.lightColor = Color.GREEN manager.createNotificationChannel(anotherChannel) with(manager.getNotificationChannel(CHANNEL_ID)) { trace("$name, $importance, 0x${Integer.toHexString(lightColor)}") } } }
65. MainActivity.kt private const val CHANNEL_ID = "channel" class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val manager = getSystemService(NotificationManager::class.java) val aChannel = NotificationChannel( CHANNEL_ID, // id "A name", // name NotificationManager.IMPORTANCE_DEFAULT // importance (3) ) aChannel.lightColor = Color.RED manager.createNotificationChannel(aChannel) manager.deleteNotificationChannel(CHANNEL_ID) val anotherChannel = NotificationChannel( CHANNEL_ID, // id "Another name", // name NotificationManager.IMPORTANCE_HIGH // importance (4) ) anotherChannel.lightColor = Color.GREEN manager.createNotificationChannel(anotherChannel) with(manager.getNotificationChannel(CHANNEL_ID)) { trace("$name, $importance, 0x${Integer.toHexString(lightColor)}") } } } B Another name, 4, 0xff00ff00 C Another name, 3, 0xff00ff00 D Another name, 3, 0xffff0000 A A name, 3, 0xffff0000
66. MainActivity.kt B Another name, 4, 0xff00ff00 C Another name, 3, 0xff00ff00 D Another name, 3, 0xffff0000 A A name, 3, 0xffff0000 private const val CHANNEL_ID = "channel" class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val manager = getSystemService(NotificationManager::class.java) val aChannel = NotificationChannel( CHANNEL_ID, // id "A name", // name NotificationManager.IMPORTANCE_DEFAULT // importance (3) ) aChannel.lightColor = Color.RED manager.createNotificationChannel(aChannel) manager.deleteNotificationChannel(CHANNEL_ID) val anotherChannel = NotificationChannel( CHANNEL_ID, // id "Another name", // name NotificationManager.IMPORTANCE_HIGH // importance (4) ) anotherChannel.lightColor = Color.GREEN manager.createNotificationChannel(anotherChannel) with(manager.getNotificationChannel(CHANNEL_ID)) { trace("$name, $importance, 0x${Integer.toHexString(lightColor)}") } } }
67. fun NotificationManager .deleteNotificationChannel( channelId: String )
68. It rather “hides”: the only possible deletion is app uninstall Doesn’t really delete fun NotificationManager .deleteNotificationChannel( channelId: String )
69. Name/description Always modifiable Mainly for i18n purposes & user-defined names/descriptions.
70. Name/description Importance Always modifiable Mainly for i18n purposes & user-defined names/descriptions. Modifiable under certain conditions Only if new importance is lower than the current one & none of the channel’s settings have been altered by the user.
71. Name/description Importance Group Always modifiable Mainly for i18n purposes & user-defined names/descriptions. Modifiable under certain conditions Modifiable under certain conditions Only if the channel has no group yet. Only if new importance is lower than the current one & none of the channel’s settings have been altered by the user.
72. Name/description Importance Group Other fields Always modifiable Mainly for i18n purposes & user-defined names/descriptions. Modifiable under certain conditions Only if new importance is lower than the current one & none of the channel’s settings have been altered by the user. Modifiable under certain conditions Only if the channel has no group yet. Never Changing seamlessly user-alterable settings would result in a bad UX.
73. Preferences read/write
74. MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val prefs = getSharedPreferences("test", Context.MODE_PRIVATE) prefs.edit() .putString("key", "hell") .apply() prefs.edit() .putString("key", null) .apply() val value = prefs.getString("key", "heaven") trace("Go to $value!") } }
75. B Go to hell! C Go to null! D Either A, B or C A Go to heaven! MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val prefs = getSharedPreferences("test", Context.MODE_PRIVATE) prefs.edit() .putString("key", "hell") .apply() prefs.edit() .putString("key", null) .apply() val value = prefs.getString("key", "heaven") trace("Go to $value!") } }
76. B Go to hell! C Go to null! D Either A, B or C A Go to heaven! MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) val prefs = getSharedPreferences("test", Context.MODE_PRIVATE) prefs.edit() .putString("key", "hell") .apply() prefs.edit() .putString("key", null) .apply() val value = prefs.getString("key", "heaven") trace("Go to $value!") } }
77. apply() is atomic async to disk
78. async to disk apply() is atomic sync to memory
79. sync to memory async to disk apply() is
81. “ defValue - String: Value to return if this preference does not exist.
82. ¯\_(ツ)_/¯ Well… not exactly
83. Null values are always considered as “not existing” so expect “defValue”
84. LinearLayout weight
85. MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) linear_layout.addOnLayoutChangeListener { v, _, _, _, _, _, _, _, _ -> trace( "LL: ${linear_layout.width}px, " + "TV1: ${text_view_1.width}px, " + "TV2: ${text_view_2.width}px" ) } } }
86. layout/activity_main.xml <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/linear_layout" android:layout_width="400px" android:layout_height="match_parent"> <TextView android:id="@+id/text_view_1" android:layout_width="300px" android:layout_height="match_parent" android:layout_weight="1" /> <TextView android:id="@+id/text_view_2" android:layout_width="200px" android:layout_height="match_parent" android:layout_weight="2" /> </LinearLayout> MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) linear_layout.addOnLayoutChangeListener { v, _, _, _, _, _, _, _, _ -> trace( "LL: ${linear_layout.width}px, " + "TV1: ${text_view_1.width}px, " + "TV2: ${text_view_2.width}px" ) } } }
87. class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) linear_layout.addOnLayoutChangeListener { v, _, _, _, _, _, _, _, _ -> trace( "LL: ${linear_layout.width}px, " + "TV1: ${text_view_1.width}px, " + "TV2: ${text_view_2.width}px" ) } } } B LL: 500px, TV1: 300px, TV2: 200px C LL: 400px, TV1: 233px, TV2: 167px D LL: 400px, TV1: 300px, TV2: 200px A LL: 400px, TV1: 267px, TV2: 133px layout/activity_main.xml <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/linear_layout" android:layout_width="400px" android:layout_height="match_parent"> <TextView android:id="@+id/text_view_1" android:layout_width="300px" android:layout_height="match_parent" android:layout_weight="1" /> <TextView android:id="@+id/text_view_2" android:layout_width="200px" android:layout_height="match_parent" android:layout_weight="2" /> </LinearLayout> MainActivity.kt
88. class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) linear_layout.addOnLayoutChangeListener { v, _, _, _, _, _, _, _, _ -> trace( "LL: ${linear_layout.width}px, " + "TV1: ${text_view_1.width}px, " + "TV2: ${text_view_2.width}px" ) } } } B LL: 500px, TV1: 300px, TV2: 200px C LL: 400px, TV1: 233px, TV2: 167px D LL: 400px, TV1: 300px, TV2: 200px A LL: 400px, TV1: 267px, TV2: 133px layout/activity_main.xml <?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/linear_layout" android:layout_width="400px" android:layout_height="match_parent"> <TextView android:id="@+id/text_view_1" android:layout_width="300px" android:layout_height="match_parent" android:layout_weight="1" /> <TextView android:id="@+id/text_view_2" android:layout_width="200px" android:layout_height="match_parent" android:layout_weight="2" /> </LinearLayout> MainActivity.kt
90. So we might end up in some very extreme & weird cases…
91. Locale resolution
92. build.gradle apply from: puzzler android { defaultConfig { resConfigs "es" } }
93. MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) // User’s locale preferences are set to: en_US, fr_FR, es_ES trace("${LocaleList.getDefault()}, " + "${Locale.getDefault()}, ${text_view.text}" ) } }
94. MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) // User’s locale preferences are set to: en_US, fr_FR, es_ES trace("${LocaleList.getDefault()}, " + "${Locale.getDefault()}, ${text_view.text}" ) } } layout/activity_main.xml <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/text_view" android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center" android:text="@string/hello_world" />
95. MainActivity.kt class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) // User’s locale preferences are set to: en_US, fr_FR, es_ES trace("${LocaleList.getDefault()}, " + "${Locale.getDefault()}, ${text_view.text}" ) } } layout/activity_main.xml <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/text_view" android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center" android:text="@string/hello_world" /> values/strings.xml <resources> <string name="hello_world">Bonjour monde !</string> </resources>
96. MainActivity.kt layout/activity_main.xml <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/text_view" android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center" android:text="@string/hello_world" /> values/strings.xml <resources> <string name="hello_world">Bonjour monde !</string> </resources> values-es/strings.xml <resources> <string name="hello_world">¡Hola mundo!</string> </resources> class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) // User’s locale preferences are set to: en_US, fr_FR, es_ES trace("${LocaleList.getDefault()}, " + "${Locale.getDefault()}, ${text_view.text}" ) } }
97. B [en_US,fr_FR,es_ES], fr_FR, Bonjour monde ! C [en_US,fr_FR,es_ES], en_US, Bonjour monde ! D Resources.NotFoundException A [fr,es], fr, Bonjour monde ! MainActivity.kt layout/activity_main.xml <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/text_view" android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center" android:text="@string/hello_world" /> values/strings.xml <resources> <string name="hello_world">Bonjour monde !</string> </resources> values-es/strings.xml <resources> <string name="hello_world">¡Hola mundo!</string> </resources> class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) // User’s locale preferences are set to: en_US, fr_FR, es_ES trace("${LocaleList.getDefault()}, " + "${Locale.getDefault()}, ${text_view.text}" ) } }
98. B [en_US,fr_FR,es_ES], fr_FR, Bonjour monde ! C [en_US,fr_FR,es_ES], en_US, Bonjour monde ! D Resources.NotFoundException A [fr,es], fr, Bonjour monde ! MainActivity.kt layout/activity_main.xml <?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/text_view" android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center" android:text="@string/hello_world" /> values/strings.xml <resources> <string name="hello_world">Bonjour monde !</string> </resources> values-es/strings.xml <resources> <string name="hello_world">¡Hola mundo!</string> </resources> class MainActivity : Activity() { override fun onCreate(savedInstanceState: Bundle?) { super.onCreate(savedInstanceState) setContentView(R.layout.activity_main) // User’s locale preferences are set to: en_US, fr_FR, es_ES trace("${LocaleList.getDefault()}, " + "${Locale.getDefault()}, ${text_view.text}" ) } }
99. User settings de_DE fr_FR es_ES App resources default es
100. User settings de_DE fr_FR es_ES App resources default es Resolution path de de_DE Children of de fr_FR fr Children of fr es_ES es Children of es Default
101. User settings de_DE fr_FR es_ES App resources default es Resolution path de de_DE Children of de fr_FR fr Children of fr es_ES es Children of es Default
102. User settings de_DE fr_FR es_ES App resources default es Resolution path de de_DE Children of de fr_FR fr Children of fr es_ES es Children of es Default
103. User settings de_DE fr_FR es_ES App resources default es Resolution path de de_DE Children of de fr_FR fr Children of fr es_ES es Children of es Default
104. User settings de_DE fr_FR es_ES App resources default es Resolution path de de_DE Children of de fr_FR fr Children of fr es_ES es Children of es Default es
105. User settings en_US fr_FR es_ES App resources default es Resolution path English is always considered as supported if in user settings
106. User settings en_US fr_FR es_ES App resources default es Resolution path en en_US Children of en fr_FR fr Children of fr es_ES es Children of es Default English is always considered as supported if in user settings
107. User settings en_US fr_FR es_ES App resources default es Resolution path en en_US Children of en fr_FR fr Children of fr es_ES es Children of es Default English is always considered as supported if in user settings
108. User settings en_US fr_FR es_ES App resources default es Resolution path en en_US Children of en fr_FR fr Children of fr es_ES es Children of es Default English is always considered as supported if in user settings default
109. That’s all folks! @cyrilmottier • cyrilmottier.com