View into the abyss

Transcript

1. VIEW INTO THE ABYSS DROIDKAIGI 2016 MORI Masaki @ SmartNews
3. Supports Android 2.2~ (Froyo)
4. This talk also works on (almost) every Android
5. VIEW “A View occupies a rectangular area on the screen and is responsible for drawing and event handling” http://developer.android.com/intl/ja/ reference/android/view/View.html
6. All you view is View
7. VIEW TREE FrameLayout LinearLayout Button ImageView TextView RelativeLayout Button
9. 3 steps to showing Views Measure - Layout - Draw
10. MEASURE Calculate size with requested constraint
11. LAYOUT Assign each position to child views
12. DRAW Render visual contents to Canvas
13. FrameLayout LinearLayout Button ImageView TextView RelativeLayout Button ViewRootImpl when setText(…) is called
14. FrameLayout LinearLayout Button ImageView TextView RelativeLayout Button ViewRootImpl requestLayout requestLayout requestLayout requestLayout View root receives requestLayout() call
15. FrameLayout LinearLayout Button ImageView TextView RelativeLayout Button ViewRootImpl measure, measure, measure, measure… measure, measure measure, measure measure measure, measure Determine sizes of all Views
16. FrameLayout LinearLayout Button ImageView TextView RelativeLayout Button ViewRootImpl layout layout layout layout layout Determine positions of all Views
17. HOW TO CUSTOM @Override void onMeasure(int widthMeasureSpec, int heightMeasureSpec) @Override void onLayout(boolean changed, int l, int t, int r, int b) (for ViewGroup)
18. onMeasure: call children’s measure() and this.setMeasuredDimension() onLayout: call children’s layout()
19. Responsive LinearLayout
20. public class AdFooter extends LinearLayout { @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { switchLayoutHorizontal(); super.onMeasure(widthMeasureSpec, heightMeasureSpec); if (isOverflowed()) { switchLayoutVertical(); super.onMeasure(widthMeasureSpec, heightMeasureSpec); } } } Responsive LinearLayout
21. PERFORMANCE TIPS Avoid requestLayout() call as much as possible
22. removeView(oldView); addView(view, index, params); removeViewInLayout(oldView); addViewInLayout(view, index, params, true); if (!isLayoutRequested()) { view.measure(widthMeasureSpec, heightMeasureSpec); view.layout(left, top, right, bottom); } SLOW FAST Replace child w/o layout
23. setImageDrawable() causes requestLayout
24. public class LayoutBlockingImageView extends ImageView { private boolean preventLayout; @Override public void setImageDrawable(Drawable drawable) { preventLayout = true; super.setImageDrawable(drawable); preventLayout = false; } @Override public void requestLayout() { if (!preventLayout) super.requestLayout(); } } Needless for fixed ImageView
25. FrameLayout LinearLayout Button ImageView TextView RelativeLayout Button ViewRootImpl setTextColor(…) called
26. FrameLayout LinearLayout Button ImageView TextView RelativeLayout Button ViewRootImpl invalidate invalidate invalidate invalidate View root receives invalidate() call
27. FrameLayout LinearLayout Button ImageView TextView RelativeLayout Button ViewRootImpl draw draw draw draw draw Render visual contents to Canvas
28. HOW TO CUSTOM setWillNotDraw(false); @Override void onDraw(Canvas canvas)
30. leftView rightView
31. @Override protected boolean drawChild(Canvas canvas, View child, long drawingTime) { canvas.save(Canvas.CLIP_SAVE_FLAG); try { if (child == leftView) { canvas.clipRect(0, 0, splitPositionLeft, height); } else if (child == rightView) { canvas.clipRect(splitPositionRight, 0, width, height); } return super.drawChild(canvas, child, drawingTime); } finally { canvas.restore(); } } Clipping child Views
32. PERFORMANCE TIPS Skip heavy jobs on animation as much as possible
33. Animating Stopped
34. Animating Stopped Kill shadows and anti-alias
35. Prefer invalidate(l, t, r, b)
36. setLayerType(LAYER_TYPE_HARDWARE) only on transition
37. REMEMBER Profile before Optimizing
38. BEST REFERENCE https://github.com/android/ platform_frameworks_base