Android Forestry (Droidcon NYC 2015)

An Android app is a forest of trees: views, contexts, navigation, and model. These hierarchical structures are distinct but often entangled, making apps complex, hard to build, and harder to understand.

This talk focuses on how Square has cleared the forest, teasing the trees apart to build simple, testable, maintainable apps. It covers the techniques we use to work with each tree individually and to manage their interactions to minimize complexity.

Transcript

1. Logan Johnson Android Forestry
2. java.lang.StackOverflowError at android.text.SpannedString.getSpans(SpannedString.java:25) at android.text.TextLine$SpanSet.init(TextLine.java:878) at android.text.TextLine.handleRun(TextLine.java:976) at android.text.TextLine.drawRun(TextLine.java:397) at android.text.TextLine.draw(TextLine.java:195) at android.text.Layout.draw(Layout.java:425) at android.text.BoringLayout.draw(BoringLayout.java:400) at android.widget.TextView.onDraw(TextView.java:5255) at android.view.View.draw(View.java:11227) at android.view.View.getDisplayList(View.java:10666) at android.view.ViewGroup.drawChild(ViewGroup.java:2858)
7. Home ItemList Bagel Croissant Settings
9. public final class MyApp extends Application {
 
 public static Bagel getBagel() { ... }
 
 }
10. User Server Database Home ItemList Bagel Croissant Settings
11. User Server Database Home ItemList Bagel Croissant Settings
12. Bagel
13. java.lang.StackOverflowError at android.text.SpannedString.getSpans(SpannedString.java:25) at android.text.TextLine$SpanSet.init(TextLine.java:878) at android.text.TextLine.handleRun(TextLine.java:976) at android.text.TextLine.drawRun(TextLine.java:397) at android.text.TextLine.draw(TextLine.java:195) at android.text.Layout.draw(Layout.java:425) at android.text.BoringLayout.draw(BoringLayout.java:400) at android.widget.TextView.onDraw(TextView.java:5255) at android.view.View.draw(View.java:11227) at android.view.View.getDisplayList(View.java:10666) at android.view.ViewGroup.drawChild(ViewGroup.java:2858) at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2497)
15. public final class MyApp extends Application {
 
 public static User getUser() { ... } public static Database getDatabase() { ... } 
 public static Server getServer() { ... } public static SellerInfo getSeller() { ... }
 
 public static Items getItems() { ... }
 
 public static Settings getSettings() { ... }
 }
16. App Settings Items Seller Bagel User, Server, Database SellerInfo
17. class View { public final Context getContext() { ... } }
18. public abstract class Context { 
 public abstract Object getSystemService(String name); 
 }
19. getContext().getSystemService(“bagel”)
20. class ContextWrapper extends Context {
 ContextWrapper(Context base) { ... }
 
 Object getSystemService(String name) {
 return mBase.getSystemService(name);
 } }
21. Object getSystemService(String name) { if (“bagel”.equals(name)) { return bagel; } 
 return baseContext.getSystemService(name);
 }
22. class View { public final Context getContext() { ... } }
23. class { public final Context getContext() { ... } } class Activity extends ContextThemeWrapper
24. class ContextThemeWrapper extends ContextWrapper { private Resources.Theme mTheme; }
25. if (LAYOUT_INFLATER_SERVICE.equals(name)) { 
 return LayoutInflater.from(baseContext) .cloneInContext(this);
 } } class ContextThemeWrapper extends ContextWrapper { private Resources.Theme mTheme;
26. Inflater + Context => View
27. getContext().getSystemService(“bagel”)
28. context.getSystemService(“dagger”) .inject(this);
29. class dagger.ObjectGraph {
 ObjectGraph plus(Object... modules);
 }
30. context.getSystemService(“dagger”) .inject(this);
31. User Server Database Home ItemList Bagel Croissant Settings
32. User Server Database Home ItemList Bagel Croissant Settings
33. class View { public final Context getContext() { ... } } class Application extends ContextWrapper class Activity extends ContextThemeWrapper
34. class View { public final Context getContext() { ... } } class Application extends ContextWrapper class Activity extends ContextThemeWrapper class Service extends ContextWrapper
35. class View { public final Context getContext() { ... } } class Application extends ContextWrapper class Activity extends ContextThemeWrapper class Service extends ContextWrapper class Application class Activity class View
36. class } class Application extends ContextWrapper class Activity extends ContextThemeWrapper class Service extends ContextWrapper class View { public final Context getContext() { ... } }
37. App Activity View
38. App Activity View
39. App Activity View User, Server, DB Bagel
40. App Activity View (Bagel)
41. Activity View (Bagel)
42. Activity View (Items) View (Bagel)
43. Activity View (Seller) View (Items) View (Bagel)
44. Items Seller Bagel
45. Home ItemList Bagel Croissant Settings
46. View (Seller) View (Items) View (Bagel)
47. View (Croissant) View (Seller) View (Items) View (Bagel)
48. View (Croissant) View (Seller) View (Items)
49. View (Croissant) View (Seller) View (Items) View (Settings)
50. class Home extends Screen 
 class Settings extends Screen class ItemList extends Screen
 class Item extends Screen {
 final String itemId; // e.g. “bagel”
 }
51. class Home extends Screen 
 class Settings extends Screen class ItemList extends Screen
 class Item extends Screen {
 final String itemId; // e.g. “bagel”
 } class Item extends Screen {
 final String itemId; // e.g. “bagel”
 }
52. Object module = getDaggerModule(screen); ObjectGraph baseGraph = base.getSystemService(DAGGER); ObjectGraph screenGraph = baseGraph.plus(module); return new ScreenContextWrapper(base, screenGraph); Context createContext(Context base, Screen screen) { }
53. Object module = getDaggerModule(screen); ObjectGraph baseGraph = base.getSystemService(DAGGER); ObjectGraph screenGraph = baseGraph.plus(module); return new ScreenContextWrapper(base, screenGraph); Context createContext(Context base, Screen screen) { }
54. Object module = getDaggerModule(screen); ObjectGraph baseGraph = base.getSystemService(DAGGER); ObjectGraph screenGraph = baseGraph.plus(module); return new ScreenContextWrapper(base, screenGraph); Context createContext(Context base, Screen screen) { }
55. Object module = getDaggerModule(screen); ObjectGraph baseGraph = base.getSystemService(DAGGER); ObjectGraph screenGraph = baseGraph.plus(module); return new ScreenContextWrapper(base, screenGraph); Context createContext(Context base, Screen screen) { }
56. Object module = getDaggerModule(screen); ObjectGraph baseGraph = base.getSystemService(DAGGER); ObjectGraph screenGraph = baseGraph.plus(module); return new ScreenContextWrapper(base, screenGraph); Context createContext(Context base, Screen screen) { }
57. if (LAYOUT_INFLATER_SERVICE.equals(name)) { 
 return LayoutInflater.from(baseContext) .cloneInContext(this);
 } } class ScreenContextWrapper extends ContextWrapper { private ObjectGraph graph;
58. Bagel Items Seller App
59. Items Seller Bagel
60. Items Seller Bagel Croissant
63. Items
66. java.lang.StackOverflowError at android.text.SpannedString.getSpans(SpannedString.java:25) at android.text.TextLine$SpanSet.init(TextLine.java:878) at android.text.TextLine.handleRun(TextLine.java:976) at android.text.TextLine.drawRun(TextLine.java:397) at android.text.TextLine.draw(TextLine.java:195) at android.text.Layout.draw(Layout.java:425) at android.text.BoringLayout.draw(BoringLayout.java:400) at android.widget.TextView.onDraw(TextView.java:5255) at android.view.View.draw(View.java:11227) at android.view.View.getDisplayList(View.java:10666) at android.view.ViewGroup.drawChild(ViewGroup.java:2858) at android.view.ViewGroup.dispatchDraw(ViewGroup.java:2497)
68. Activity View View … StackOverflowErr
69. Items Seller Bagel
70. Item{Bagel} Items Seller App
72. class Seller extends Screen class Items extends Seller class Item extends Items {
 final String itemId; // e.g. “bagel”
 }
73. class Seller extends Screen class Items extends Seller class Item extends Items {
 final String itemId; // e.g. “bagel”
 } Seller extends Screen Items extends Seller Item extends Items
74. Item{bagel}
75. Item{bagel} /App/Seller/Items/
76. Item{bagel} /
77. class Item extends Path {
 final String itemId; // e.g. “bagel”
 
 @Override Path buildAbsolute(Builder abs) {
 return Path.root() .append(new Seller()) .append(new Items()) .append(this);
 }
 }
78. Item{Bagel}
79. Items Seller Activity
80. Items Seller Activity Activity
81. Activity
82. Activity
84. Bagel
85. Bagel
86. Bagel
91. minSdkVersion 19 android.transition.Transition
92. minSdkVersion 15 android.animation.Animator
93. static class MainActivity extends Activity {
 
 void navigate(Path fromPath, Path toPath) {
 // ...
 } }
94. public final class IncomingOrderDialog
95. @AnalyticsName(NEW_ORDER_POPUP) @SuppressPopups @DisablesBackButton @SessionFilter(AUTHENTICATED) @NotPersistent @Dialog @Layout(R.layout.incoming_order_dialog) public final class IncomingOrderDialog
96. @AnalyticsName(NEW_ORDER_POPUP) @SuppressPopups @DisablesBackButton @SessionFilter(AUTHENTICATED) @NotPersistent @Dialog @Layout(R.layout.incoming_order_dialog) public final class IncomingOrderDialog
97. @AnalyticsName(NEW_ORDER_POPUP) @SuppressPopups @DisablesBackButton @SessionFilter(AUTHENTICATED) @NotPersistent @Dialog @Layout(R.layout.incoming_order_dialog) public final class IncomingOrderDialog
98. @AnalyticsName(NEW_ORDER_POPUP) @SuppressPopups @DisablesBackButton @SessionFilter(AUTHENTICATED) @NotPersistent @Dialog @Layout(R.layout.incoming_order_dialog) public final class IncomingOrderDialog
99. @AnalyticsName(NEW_ORDER_POPUP) @SuppressPopups @DisablesBackButton @SessionFilter(AUTHENTICATED) @NotPersistent @Dialog @Layout(R.layout.incoming_order_dialog) public final class IncomingOrderDialog
100. @AnalyticsName(NEW_ORDER_POPUP) @SuppressPopups @DisablesBackButton @SessionFilter(AUTHENTICATED) @NotPersistent @Dialog @Layout(R.layout.incoming_order_dialog) public final class IncomingOrderDialog
101. @AnalyticsName(NEW_ORDER_POPUP) @SuppressPopups @DisablesBackButton @SessionFilter(AUTHENTICATED) @NotPersistent @Dialog @Layout(R.layout.incoming_order_dialog) public final class IncomingOrderDialog
102. @AnalyticsName(NEW_ORDER_POPUP) @SuppressPopups @DisablesBackButton @SessionFilter(AUTHENTICATED) @NotPersistent @Dialog @Layout(R.layout.incoming_order_dialog) public final class IncomingOrderDialog
103. @AnalyticsName(NEW_ORDER_POPUP) @SuppressPopups @DisablesBackButton @SessionFilter(AUTHENTICATED) @NotPersistent @Dialog @Layout(R.layout.incoming_order_dialog) public final class IncomingOrderDialog
104. public final class IncomingOrderDialog {
 
 @dagger.Module(..)
 public static final class Module {
 } 
 }
105. @WithResponsiveModule(
 tablet = TabletModule.class, //
 mobile = MobileModule.class) // public final class HomeScreen
106. class MainActivity extends Activity {
 
 @Override protected void onNewIntent(Intent intent) {
 navigate(null, getPath(intent)); }
 }
107. class MainActivity extends Activity {
 
 @Override protected void onCreate(Bundle saved) {
 navigate(null, getPath(saved));
 } }
109. @loganj