Layout Traversals (GDG Devfest 2014)

Presented at GDG Devfest London 2014

1. LAYOUT TRAVERSALS Devfest London, 2014
2. LUCAS ROCHA +LucasRocha | @lucasratmundo
4. BE DELIBERATE Less handwaviness in your UI code
5. UI TOOLKITS Layout + Rendering + Input Events
6. TICK TOCK VSYNC sets the pace.
7. CHOREOGRAPHER f1 f2 f3 f4 f5 . . . . . . VSYNC (60fps) Resize view Redraw view Input Events
8. CHOREOGRAPHER public void onVsync(long timestampNanos, int builtInDisplayId, int frame) { ... scheduleVsync(); ... } ... void doFrame(long frameTimeNanos, int frame) { ... if (!mFrameScheduled) { return; } ... doCallbacks(Choreographer.CALLBACK_INPUT, frameTimeNanos); doCallbacks(Choreographer.CALLBACK_ANIMATION, frameTimeNanos); doCallbacks(Choreographer.CALLBACK_TRAVERSAL, frameTimeNanos); ... } Choreographer.java
9. ViewRootImpl Connects WindowManager with the View framework
10. ViewRootImpl *
11. FRAMEWORK Measure + Layout + Draw
12. TRAVERSAL * performTraversals() f2 performTraversals()
13. MEASURE * measure(int, int) f2 M M M M M M → onMeasure(int, int) measureHierarchy(...)
14. LAYOUT * f2 M L M L M L M L M L M L layout(int, int, int, int) → onLayout(boolean, int, int, int, int) performLayout()
15. DRAW * f2 M L D M L D M L D M L D M L D M L D draw(Canvas) → onDraw(Canvas) performDraw()
16. CHANGES Resize, redraw & animate.
17. * requestLayout() f1 f2 f3 f4 f5 . . . . . .
18. requestLayout() public void requestLayout() { ... if (mParent != null && !mParent.isLayoutRequested()) { mParent.requestLayout(); } ... } void scheduleTraversals() { ... mTraversalBarrier = mHandler.getLooper().postSyncBarrier(); mChoreographer.postCallback( Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null); ... } View.java ViewRootImpl.java
19. * Invalidate(...) f1 f2 f3 f4 f5 . . . . . .
20. invalidate(...) public void invalidateInternal(...) { ... mPrivateFlags |= PFLAG_DIRTY; ... if (mParent != null && mAttachInfo != null && l < r && t < b) { final Rect damage = mAttachInfo.mTmpInvalRect; damage.set(l, t, r, b); mParent.invalidateChild(this, damage); } ... } View.java
21. * postOnAnimation() f1 f2 f3 f4 f5 . . . . . . ValueAnimator ...
22. postOnAnimation() public void postOnAnimation(Runnable action) { ... attachInfo.mViewRootImpl.mChoreographer.postCallback( Choreographer.CALLBACK_ANIMATION, action, null); ... } void doFrame(long frameTimeNanos, int frame) { ... doCallbacks(Choreographer.CALLBACK_INPUT, frameTimeNanos); doCallbacks(Choreographer.CALLBACK_ANIMATION, frameTimeNanos); doCallbacks(Choreographer.CALLBACK_TRAVERSAL, frameTimeNanos); ... } View.java Choreographer.java
23. LAZY MEASURE Multi-MeasureSpec cache, invalidated in requestLayout()
24. LAZY MEASURE public final void measure(int widthMeasureSpec, int heightMeasureSpec) { ... int cacheIndex = mMeasureCache.indexOfKey(key); if (cacheIndex < 0 || sIgnoreMeasureCache) { onMeasure(widthMeasureSpec, heightMeasureSpec); mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT; } else { long value = mMeasureCache.valueAt(cacheIndex); setMeasuredDimensionRaw((int) (value >> 32), (int) value); mPrivateFlags3 |= PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT; } ... } View.java
25. LAZY MEASURE public void layout(int l, int t, int r, int b) { if ((flags & PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT) != 0) { onMeasure(mOldWidthMeasureSpec, mOldHeightMeasureSpec); mPrivateFlags3 &= ~PFLAG3_MEASURE_NEEDED_BEFORE_LAYOUT; } ... } View.java
26. BASIC TIPS 1. No layout requests during layout 2. No layout requests during animations 3. Invalidate regions when possible
27. PERFORMANCE 1. Simplify your view hierarchy 2. Avoid multi-pass measurement
28. GO CUSTOM Simplify view hierarchy, performance, missing features. http://lucasr.org/?p=3920
29. TREE OBSERVER Use OnPreDrawListener!
30. TRANSITIONS http://lucasr.org/?p=3902
31. OnPreDrawListener // 1. Save layout state and wait for next frame. getViewTreeObserver().addOnPreDrawListener(new OnPreDrawListener() { @Override public boolean onPreDraw() { getViewTreeObserver().removeOnPreDrawListener(this); // 2. Restore original layout state. // 3. Trigger animators towards new layout state. } }
32. PROBE IT! Intercept view methods. Dissect layout traversals. https://github.com/lucasr/probe
33. OVERRIDE VIEW METHODS public class DrawGreen extends Interceptor { private final Paint mPaint; public DrawGreen() { mPaint = new Paint(); mPaint.setColor(Color.GREEN); } @Override public void onDraw(View view, Canvas canvas) { canvas.drawPaint(mPaint); } }
34. DEPLOY public final class MainActivity extends Activity { @Override protected void onCreate(Bundle savedInstanceState) { Probe.deploy(this, new DrawGreen(), new Filter.ViewId(R.id.view2)); super.onCreate(savedInstanceState); setContentView(R.id.main_activity); } }
35. WRAP VIEW METHODS public class LogRequestLayout extends Interceptor { @Override public void requestLayout(View view) { super.requestLayout(view); Log.d(LOGTAG, “requestLayout() on ” + view); } }
36. QUESTIONS? +LucasRocha | @lucasratmundo