Introduction of Android View
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This document provides an overview of Android Views and ViewGroups. It discusses key concepts like attaching and detaching Views from windows, measuring and laying out Views, drawing Views, and debugging Views. The presenter then covers topics like View mechanisms, attaching and detaching from windows, measuring, layout, drawing, and live debugging. Additional topics discussed include hardware acceleration, SurfaceViews, and regular meetups for technical sharing.
Introduction of Android View
- 2. Charlie Tsai@Android Study Group cha122977@gmail.com Individual App Developer & System Software Engineer@NVIDIA (will quit in Sep.) Today’s source code https://github.com/chatea/ViewDemo
- 3. Agenda • View & ViewGroup • Mechanism of View • Live debugging • Free topics :D
- 4. View • Attached to window / Detached from window • Measure • Layout • Draw
- 5. ViewGroup • ViewGroup extend View (composition pattern) • The draw functions are different: • View.onDraw(Canvas); • ViewGroup.dispatchDraw(Canvas);
- 6. Mechanism of View • What does View do? • What does View NOT do? • Need to attach to Window • measure: analysis the size of view • layout: determine the position and size of view • draw: real function to render the View
- 7. Mechanism of View • Draw from parent, then to children • Canvas is given by Android framework • Cost of overlay?
- 8. Attach / Detach • onAttachedToWindow() / onDetachedFromWindow() • What is Window? • WindowManager • ViewRootImpl (composition pattern) • interactive with WindowManager • performTraversals() & scheduleTraversals() • own the Surface and send Canvas to View
- 9. Measure • How big this View should be? • void onMeasure(int, int) • setMeasuredDimension(int, int)
- 10. Ex: Square View
- 11. Layout • Assign the size and position to self and all descendants • onLayout(boolean changed, l, t, r b) • addOnLayoutChangeListener(…)
- 12. Draw • Should I use super.onDraw(Canvas)? • View.onDraw(): hook for customized drawing • Why ViewGroup.dispatchDraw()?
- 13. Live Debugging
- 14. Let’s Go Deeper…
- 15. Hardware Acceleration • View.setLayerType(…) • LAYER_TYPE_NONE • LAYER_TYPE_HARDWARE • LAYER_TYPE_SOFTWARE
- 16. Hardware Acceleration • save() -> setXXX -> draw -> restore() • setXXX - a function which doesn’t effect the content • e.g. setX(), setY(), setRotation()…
- 17. SurfaceView • SurfaceView doesn’t render from parent • System directly maintain its Canvas • Transparent SurfaceView? • SurfaceView.setZOrderOnTop() • SurfaceView.getHolder().setFormat(PixelForm at.TRANSPARENT);
- 19. Questions?
- 20. Thanks!