Secrets of the Support Library (Droidcon NYC 2016)

The support library has become a necessity for the majority of Android developers. This talk will delve into some of its secrets, from bugs we’ve fixed, things we haven’t (yet), and how some of the features you’re using actually work back to API 9.

1. SECRETS OF THE SUPPORT LIBRARY +ChrisBanes @chrisbanes
2. SECRETS OF THE SUPPORT LIBRARY banes.me/dcnyc16 http://
3. SECRETS OF THE SUPPORT LIBRARY DayNight
4. Allows your app to be automatically themed based on time of day
5. Allows your app to be automatically themed based on time of day
6. AppCompatDelegate.setDefaultNightMode(...) Change night mode Change theme Theme.AppCompat.DayNight
7. MODE_NIGHT_FOLLOW_SYSTEM Follows the system night mode DEFAULT MODE_NIGHT_YES Always night mode MODE_NIGHT_NO Never night mode (aka day mode) MODE_NIGHT_AUTO Switches based on time of day
8. MODE_NIGHT_FOLLOW_SYSTEM Follows the system night mode DEFAULT MODE_NIGHT_YES Always night mode MODE_NIGHT_NO Never night mode (aka day mode) MODE_NIGHT_AUTO Switches based on time of day
9. MODE_NIGHT_FOLLOW_SYSTEM Follows the system night mode DEFAULT MODE_NIGHT_YES Always night mode MODE_NIGHT_NO Never night mode (aka day mode) MODE_NIGHT_AUTO Switches based on time of day
10. Night mode has existed since API 8 -night -notnight
11. Car mode Docked ⚓ © Philip Greenspun
12. public final class Configuration { // Lots of other configuration fields public int uiMode; }
13. public static final int UI_MODE_NIGHT_MASK;
 public static final int UI_MODE_NIGHT_UNDEFINED; public static final int UI_MODE_NIGHT_NO; public static final int UI_MODE_NIGHT_YES;
14. public static final int UI_MODE_NIGHT_MASK;
 public static final int UI_MODE_NIGHT_UNDEFINED; public static final int UI_MODE_NIGHT_NO; public static final int UI_MODE_NIGHT_YES;
15. public static final int UI_MODE_NIGHT_MASK;
 public static final int UI_MODE_NIGHT_UNDEFINED; public static final int UI_MODE_NIGHT_NO; public static final int UI_MODE_NIGHT_YES;
16. public static final int UI_MODE_NIGHT_NO; public static final int UI_MODE_NIGHT_YES; AppCompatDelegate.MODE_NIGHT_NO AppCompatDelegate.MODE_NIGHT_YES
17. Resources res = getResources(); Configuration config = res.getConfiguration(); // Update the UI Mode to reflect the new night mode config.uiMode = newNightMode | (config.uiMode & ~Configuration.UI_MODE_NIGHT_MASK); // Now update the configuration res.updateConfiguration(config, ...);
18. Resources res = getResources(); Configuration config = res.getConfiguration(); // Update the UI Mode to reflect the new night mode config.uiMode = newNightMode | (config.uiMode & ~Configuration.UI_MODE_NIGHT_MASK); // Now update the configuration res.updateConfiguration(config, ...); Configuration.UI_MODE_NIGHT_YES
19. Resources res = getResources(); Configuration config = res.getConfiguration(); // Update the UI Mode to reflect the new night mode config.uiMode = newNightMode | (config.uiMode & ~Configuration.UI_MODE_NIGHT_MASK); // Now update the configuration res.updateConfiguration(config, ...);
20. values-night drawable-night raw-night
21. <style name="Theme.AppCompat.DayNight" parent=“Theme.AppCompat.Light" /> <style name="Theme.AppCompat.DayNight" parent="Theme.AppCompat" /> res/values-night res/values
22. SECRETS OF THE SUPPORT LIBRARY AppBarLayout & flinging http://b.android.com/179501
23. User swipes up, collapsing the AppBarLayout and scrolling the list
24. User swipes down, scrolling the list
25. User needs to swipe down again, to expand the AppBarLayout
26. The problem: Flinging does not transfer left over velocity
27. The goal: Flinging transfers velocity when it reaches the end
28. > SECRETS OF THE SUPPORT LIBRARY Basic Scrolling APPBARLAYOUT FLINGING
29. onTouchEvent(MotionEvent) onInterceptTouchEvent(MotionEvent) There’s also but we’ll skip that
30. ACTION_DOWN
31. ACTION_DOWN // ev = MotionEvent parameter // Initialise VelocityTracker and add event mVelocityTracker = VelocityTracker.obtain(); mVelocityTracker.addMovement(ev); int y = ev.getY(); // 1020 mLastMotionY = y;
32. ACTION_MOVE A scroll is usually made up with 100s of events
33. ACTION_MOVE // Add event to velocity tracker mVelocityTracker.addMovement(ev); int y = ev.getY(); // 1010 // Calculate difference from last event int dy = mLastMotionY - y; // -10 for (int i = 0; i < getChildCount(); i++) { View child = getChildAt(i); child.offsetTopAndBottom(dy); }A

34. ACTION_MOVE // Add event to velocity tracker mVelocityTracker.addMovement(ev); int y = ev.getY(); // 1010 // Calculate difference from last event int dy = mLastMotionY - y; // -10 for (int i = 0; i < getChildCount(); i++) { View child = getChildAt(i); child.offsetTopAndBottom(dy); }A
 // Finally update our recorded Y mLastMotionY = y;
35. ACTION_UP
36. ACTION_UP // Calculate velocity over 1000ms mVelocityTracker.computeCurrentVelocity(1000); float velY = mVelocityTracker.getYVelocity(); // TODO Implement some flinging fling(velY);
37. OverScroller mScroller = new OverScroller(); void fling(int velocityY) { // How much we can scroll int scrollRange = ...; mScroller.fling(mScrollX, mScrollY, 0, velocityY, 0, 0, 0, scrollRange, 0, height / 2); ViewCompat.postInvalidateOnAnimation(this); }
38. OverScroller mScroller = new OverScroller(); void fling(int velocityY) { // How much we can scroll int scrollRange = ...; mScroller.fling(mScrollX, mScrollY, 0, velocityY, 0, 0, 0, scrollRange, 0, height / 2); ViewCompat.postInvalidateOnAnimation(this); }
39. OverScroller mScroller = new OverScroller(); void fling(int velocityY) { // How much we can scroll int scrollRange = ...; mScroller.fling(mScrollX, mScrollY, 0, velocityY, 0, 0, 0, scrollRange, 0, height / 2); ViewCompat.postInvalidateOnAnimation(this); } // Passed in from touch handling
40. OverScroller mScroller = new OverScroller(); void fling(int velocityY) { // How much we can scroll int scrollRange = ...; mScroller.fling(mScrollX, mScrollY, 0, velocityY, 0, 0, 0, scrollRange, 0, height / 2); ViewCompat.postInvalidateOnAnimation(this); }
41. OverScroller mScroller = new OverScroller(); void fling(int velocityY) { // How much we can scroll int scrollRange = ...; mScroller.fling(mScrollX, mScrollY, 0, velocityY, 0, 0, 0, scrollRange, 0, height / 2); ViewCompat.postInvalidateOnAnimation(this); }
42. OverScroller mScroller = new OverScroller(); void fling(int velocityY) { // How much we can scroll int scrollRange = ...; mScroller.fling(mScrollX, mScrollY, 0, velocityY, 0, 0, 0, scrollRange, 0, height / 2); ViewCompat.postInvalidateOnAnimation(this); } // Current scroll position
43. OverScroller mScroller = new OverScroller(); void fling(int velocityY) { // How much we can scroll int scrollRange = ...; mScroller.fling(mScrollX, mScrollY, 0, velocityY, 0, 0, 0, scrollRange, 0, height / 2); ViewCompat.postInvalidateOnAnimation(this); } // Fling velocity
44. OverScroller mScroller = new OverScroller(); void fling(int velocityY) { // How much we can scroll int scrollRange = ...; mScroller.fling(mScrollX, mScrollY, 0, velocityY, 0, 0, 0, scrollRange, 0, height / 2); ViewCompat.postInvalidateOnAnimation(this); } // minX, maxX
45. OverScroller mScroller = new OverScroller(); void fling(int velocityY) { // How much we can scroll int scrollRange = ...; mScroller.fling(mScrollX, mScrollY, 0, velocityY, 0, 0, 0, scrollRange, 0, height / 2); ViewCompat.postInvalidateOnAnimation(this); } // minY, maxY
46. OverScroller mScroller = new OverScroller(); void fling(int velocityY) { // How much we can scroll int scrollRange = ...; mScroller.fling(mScrollX, mScrollY, 0, velocityY, 0, 0, 0, scrollRange, 0, height / 2); ViewCompat.postInvalidateOnAnimation(this); } // overscroll X, Y
47. OverScroller mScroller = new OverScroller(); void fling(int velocityY) { // How much we can scroll int scrollRange = ...; mScroller.fling(mScrollX, mScrollY, 0, velocityY, 0, 0, 0, scrollRange, 0, height / 2); ViewCompat.postInvalidateOnAnimation(this); }
48. @Override public void computeScroll() { if (mScroller.computeScrollOffset()) { int x = mScroller.getCurrX(); int y = mScroller.getCurrY(); // Update the scroll position scrollTo(x, y); } }
49. > SECRETS OF THE SUPPORT LIBRARY Nested Scrolling APPBARLAYOUT FLINGING
50. Nested scrolling views was difficult
51. Nested scrolling views was difficult <ScrollView> <LinearLayout> <!-- Some content --> <ListView> <!-- More content which scrolls --> </ListView> </LinearLayout> </ScrollView>
53. <ScrollView> <LinearLayout> 
 </LinearLayout> </ScrollView>
54. <ScrollView> <LinearLayout> <ImageView /> </LinearLayout> </ScrollView>
55. <ScrollView> <LinearLayout> <ImageView /> <ListView /> </LinearLayout> </ScrollView>
56. Nested scrolling was created to solve this
57. An event system where scroll events are dispatched up the view hierarchy
58. ScrollView LinearLayout ImageView ListView
59. void setNestedScrollingEnabled(boolean enabled); boolean isNestedScrollingEnabled(); boolean startNestedScroll(int axes); boolean hasNestedScrollingParent(); boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed,
 int[] offsetInWindow); boolean dispatchNestedScroll(int dxConsumed, int dyConsumed,
 int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow); boolean dispatchNestedPreFling(float velocityX, float velocityY); boolean dispatchNestedFling(float velocityX, float velocityY,
 boolean consumed); void stopNestedScroll(); Sending
60. void setNestedScrollingEnabled(boolean enabled); boolean isNestedScrollingEnabled(); boolean startNestedScroll(int axes); boolean hasNestedScrollingParent(); boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed,
 int[] offsetInWindow); boolean dispatchNestedScroll(int dxConsumed, int dyConsumed,
 int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow); boolean dispatchNestedPreFling(float velocityX, float velocityY); boolean dispatchNestedFling(float velocityX, float velocityY,
 boolean consumed); void stopNestedScroll(); Sending
61. boolean dispatchNestedPreScroll(int dx, int dy, int[] consumed,
 int[] offsetInWindow); boolean dispatchNestedScroll(int dxConsumed, int dyConsumed,
 int dxUnconsumed, int dyUnconsumed, int[] offsetInWindow); boolean dispatchNestedPreFling(float velocityX, float velocityY); boolean dispatchNestedFling(float velocityX, float velocityY,
 boolean consumed); Sending
62. boolean onStartNestedScroll(View child, View target,
 int nestedScrollAxes); void onNestedScrollAccepted(View child, View target,
 int nestedScrollAxes); void onStopNestedScroll(View target); int getNestedScrollAxes(); Receiving void onNestedPreScroll(View target, int dx, int dy, int[] consumed); void onNestedScroll(View target, int dxConsumed, int dyConsumed,
 int dxUnconsumed, int dyUnconsumed); boolean onNestedPreFling(View target, float velocityX,
 float velocityY); boolean onNestedFling(View target, float velocityX,
 float velocityY, boolean consumed);
63. boolean onStartNestedScroll(View child, View target,
 int nestedScrollAxes); void onNestedScrollAccepted(View child, View target,
 int nestedScrollAxes); void onStopNestedScroll(View target); int getNestedScrollAxes(); Receiving void onNestedPreScroll(View target, int dx, int dy, int[] consumed); void onNestedScroll(View target, int dxConsumed, int dyConsumed,
 int dxUnconsumed, int dyUnconsumed); boolean onNestedPreFling(View target, float velocityX,
 float velocityY); boolean onNestedFling(View target, float velocityX,
 float velocityY, boolean consumed);
64. Receiving void onNestedPreScroll(View target, int dx, int dy, int[] consumed); void onNestedScroll(View target, int dxConsumed, int dyConsumed,
 int dxUnconsumed, int dyUnconsumed); boolean onNestedPreFling(View target, float velocityX,
 float velocityY); boolean onNestedFling(View target, float velocityX,
 float velocityY, boolean consumed);
65. Two things to know about the API…
66. Sending (scrolling view) boolean dispatchNestedPreScroll(int dx, int dy,
 int[] consumed, int[] offsetInWindow); Receiving (parent) void onNestedPreScroll(View target, int dx, int dy,
 int[] consumed);
67. Pre vs Non-Pre Scroll events allow the parent to observe what the view scrolled The view then scrolls the remainder Pre-scroll events allow a parent to intercept and consume the event
68. Let’s see how it happens…
69. ACTION_DOWN
70. ACTION_DOWN // Initialise VelocityTracker and add event mVelocityTracker.addMovement(ev); int y = ev.getY(); // 1020 mInitialMotionY = y; mLastMotionY = y; startNestedScroll(SCROLL_AXIS_VERTICAL);
71. ACTION_DOWN startNestedScroll(SCROLL_AXIS_VERTICAL); // Initialise VelocityTracker and add event mVelocityTracker.addMovement(ev); int y = ev.getY(); // 1020 mInitialMotionY = y; mLastMotionY = y;
72. ACTION_DOWN startNestedScroll(SCROLL_AXIS_VERTICAL); @Override boolean onStartNestedScroll(View child, View target, int axes) { // child == LinearLayout // target == ListView // axes == SCROLL_AXIS_VERTICAL return true; }
73. ACTION_DOWN startNestedScroll(SCROLL_AXIS_VERTICAL); @Override void onNestedScrollAccepted(View child, View target, int axes) { // child == LinearLayout // target == ListView // axes == SCROLL_AXIS_VERTICAL }
74. ACTION_MOVE
75. ACTION_MOVE int[] mScrollConsumed = new int[2]; int y = ev.getY(); // 1010 int dy = mLastMotionY - y; // -10 if (dispatchNestedPreScroll(0, dy, mScrollConsumed, ...)) { dy -= mScrollConsumed[1]; } // INSERT Move children by remaining dy // TODO call dispatchNestedScroll()
76. ACTION_MOVE @Override void onNestedPreScroll(View target, int dx, int dy, int[] consumed) { // dx = 0, dy = -10, consumed = int[2] int amountWeConsume = doSomethingWithPreScroll(dy); // consumed[0] = y, consumed[1] = x consumed[1] = amountWeConsume; } dispatchNestedPreScroll(0, dy, mScrollConsumed, ...)
77. ACTION_MOVE int[] mScrollConsumed = new int[2]; int y = ev.getY(); // 1010 int dy = mLastMotionY - y; // -10 if (dispatchNestedPreScroll(0, dy, mScrollConsumed, ...)) { dy -= mScrollConsumed[1]; } // INSERT Move children by remaining dy // TODO call dispatchNestedScroll() // -3 remember // dy = -7
78. ACTION_MOVE int[] mScrollConsumed = new int[2]; int y = ev.getY(); // 1010 int dy = mLastMotionY - y; // -10 if (dispatchNestedPreScroll(0, dy, mScrollConsumed, ...)) { dy -= mScrollConsumed[1]; } // INSERT Move children by remaining dy // TODO call dispatchNestedScroll()
79. ACTION_MOVE // INSERT Move children by remaining dy // TODO call dispatchNestedScroll()
80. ACTION_MOVE // INSERT Move children by remaining dy dispatchNestedScroll(0, dy, 0, unconsumedY, ...) @Override void onNestedScroll(View target,
 int dxConsumed, int dyConsumed, int dxUnconsumed, int dyUnconsumed) { // Do something if you wish }
81. ACTION_UP // Calculate velocity over 1000ms mVelocityTracker.computeCurrentVelocity(1000); float velY = mVelocityTracker.getYVelocity(); fling(velY);
82. ACTION_UP float velY = ...; if (!dispatchNestedPreFling(0, velY)) { // Parent hasn't consumed fling, lets fling // and let the parent observe dispatchNestedFling(0, velY, ...); fling(velY); } stopNestedScroll();
83. ACTION_UP float velY = ...; if (!dispatchNestedPreFling(0, velY)) { // Parent hasn't consumed fling, lets fling // and let the parent observe dispatchNestedFling(0, velY, ...); fling(velY); } stopNestedScroll();
84. ACTION_UP dispatchNestedPreFling(0, velY); @Override boolean onNestedPreFling(View target, float velX, float velY) { // return true to consume the whole fling, // false to let the view handle it }
85. ACTION_UP float velY = ...; if (!dispatchNestedPreFling(0, velY)) { // Parent hasn't consumed fling, lets fling // and let the parent observe dispatchNestedFling(0, velY, ...); fling(velY); } stopNestedScroll();
86. ACTION_UP float velY = ...; if (!dispatchNestedPreFling(0, velY)) { // Parent hasn't consumed fling, lets fling // and let the parent observe dispatchNestedFling(0, velY, ...); fling(velY); } stopNestedScroll();
87. The problem: Flinging does not transfer left over velocity
88. The problem: Nested flinging does not allow interception like scrolling
89. > SECRETS OF THE SUPPORT LIBRARY Indirect Nested Scrolling APPBARLAYOUT FLINGING Work in progress
90. Nested scrolling
91. Direct nested scrolling User directly touching screen
92. User not directly touching screen Indirect nested scrolling
93. Settling from fling Setting scroll position programmatically Scrolling from KeyEvents ?
94. void setNestedIndirectScrollingEnabled(boolean enabled); boolean isNestedIndirectScrollingEnabled(); boolean startNestedIndirectScroll(int axes); boolean dispatchNestedIndirectPreScroll(int dx, int dy,
 int[] consumed); boolean dispatchNestedIndirectScroll(int dxConsumed,
 int dyConsumed, int dxUnconsumed, int dyUnconsumed); boolean hasNestedIndirectScrollingParent(); void stopNestedIndirectScroll(); Sending
95. boolean onStartNestedIndirectScroll(View child, View target,
 int axes); void onNestedIndirectScrollAccepted(View child, View target,
 int axes); void onNestedIndirectPreScroll(View target, int dx, int dy,
 int[] consumed); void onNestedIndirectScroll(View target, int dxConsumed,
 int dyConsumed, int dxUnconsumed, int dyUnconsumed); void onStopNestedIndirectScroll(View child); Receiving
96. API is mostly the same as nested scrolling
97. Fling API is mostly the same as nested scrolling Works with nested scrolling
98. startNestedScroll(...) ACTION_DOWN
99. dispatchNestedPreScroll(...) dispatchNestedScroll(...) ACTION_MOVE
100. ACTION_MOVE
101. stopNestedScroll() ACTION_UP fling() startNestedIndirectScroll(...) ↳
102. dispatchNestedIndirectPreScroll(...) dispatchNestedIndirectScroll(...)
103. stopNestedIndirectScroll()
104. Over and out… +ChrisBanes @chrisbanes