我是靠谱客的博主 淡定帆布鞋,这篇文章主要介绍Android性能优化第(十 一)篇---卡顿分析,正确评测流畅度,现在分享给大家,希望可以做个参考。

一、FPS评测应用流畅度不准确

说到应用的流畅度,都会想到FPS,系统获取FPS的原理是:手机屏幕显示的内容是通过Android系统的SurfaceFLinger类,把当前系统里所有进程需要显示的信息合成一帧,然后提交到屏幕上进行显示,FPS就是1秒内SurfaceFLinger提交到屏幕的帧数。用FPS来评测一个应用是否真的卡顿存在两个问题。
- 有的时候FPS很低,APP看起来却很流畅;
- APP停止操作之后,FPS还是在一直变化,这种情况是否会影响到FPS的准确度?
有的时候FPS很低,APP看起来却很流畅,是因为当前界面在1秒内只需要10帧的显示需求,当然不会卡顿,此时FPS只要高于10就可以了,如果屏幕根本没有绘制需求,那FPS的值就是0。

Android性能优化第(四)篇—Android渲染机制说过,Android系统每隔16ms发出VSYNC信号,触发对UI的渲染,16ms没完成绘制就会卡顿。VSync机制就像是一台转速固定的发动机(60转/s)。每一转会带动着去做一些UI相关的事情,但不是每一转都会有工作去做(就像有时在空挡,有时在D档)。有时候因为各种阻力某一圈工作量比较重超过了16.6ms,那么这台发动机这秒内就不是60转了,当然也有可能被其他因素影响,比如给油不足(主线程里干的活太多)等等,就会出现转速降低的状况。我们把这个转速叫做流畅度。当流畅度越小的时候说明当前程序越卡顿。

二、Choreographer帧率检测原理

我们有时候会看到这样的log,系统帮助我们打印出了跳帧数。

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02-07 19:47:04.333 17601-17604/zhangwan.wj.com.choreographertest D/dalvikvm: GC_CONCURRENT freed 143K, 3% free 9105K/9384K, paused 2ms+0ms, total 6ms 02-07 19:47:04.337 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 60 frames! The application may be doing too much work on its main thread. 02-07 19:47:11.685 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 85 frames! The application may be doing too much work on its main thread. 02-07 19:47:12.545 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 37 frames! The application may be doing too much work on its main thread. 02-07 19:47:14.893 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 37 frames! The application may be doing too much work on its main thread. 02-07 19:47:23.049 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 36 frames! The application may be doing too much work on its main thread. 02-07 19:47:23.929 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 37 frames! The application may be doing too much work on its main thread. 02-07 19:47:24.961 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 61 frames! The application may be doing too much work on its main thread. 02-07 19:47:25.817 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 36 frames! The application may be doing too much work on its main thread. 02-07 19:47:26.433 17601-17601/zhangwan.wj.com.choreographertest I/Choreographer: Skipped 36 frames! The application may be doing too much work on its main thread.

这个log就出自于Choreographer中(英[ˌkɒrɪ’ɒɡrəfə(r)] 美[ˌkɒrɪ’ɒɡrəfə(r)])。

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void doFrame(long frameTimeNanos, int frame) { final long startNanos; synchronized (mLock) { if (!mFrameScheduled) { return; // no work to do } if (DEBUG_JANK && mDebugPrintNextFrameTimeDelta) { mDebugPrintNextFrameTimeDelta = false; Log.d(TAG, "Frame time delta: " + ((frameTimeNanos - mLastFrameTimeNanos) * 0.000001f) + " ms"); } long intendedFrameTimeNanos = frameTimeNanos; startNanos = System.nanoTime(); final long jitterNanos = startNanos - frameTimeNanos; if (jitterNanos >= mFrameIntervalNanos) { final long skippedFrames = jitterNanos / mFrameIntervalNanos; if (skippedFrames >= SKIPPED_FRAME_WARNING_LIMIT) { Log.i(TAG, "Skipped " + skippedFrames + " frames! " + "The application may be doing too much work on its main thread."); } final long lastFrameOffset = jitterNanos % mFrameIntervalNanos; if (DEBUG_JANK) { Log.d(TAG, "Missed vsync by " + (jitterNanos * 0.000001f) + " ms " + "which is more than the frame interval of " + (mFrameIntervalNanos * 0.000001f) + " ms! " + "Skipping " + skippedFrames + " frames and setting frame " + "time to " + (lastFrameOffset * 0.000001f) + " ms in the past."); } frameTimeNanos = startNanos - lastFrameOffset; } } }

其中SKIPPED_FRAME_WARNING_LIMIT是Choreographer的成员变量。

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// Set a limit to warn about skipped frames. // Skipped frames imply jank. private static final int SKIPPED_FRAME_WARNING_LIMIT =SystemProperties.getInt( "debug.choreographer.skipwarning", 30);

也就是当跳帧数大于设置的SKIPPED_FRAME_WARNING_LIMIT 值时会在当前进程输出这个log。由于 SKIPPED_FRAME_WARNING_LIMIT 的值默认为 30,所以上面的log并不是经常看到,如果我们用反射的方法把SKIPPED_FRAME_WARNING_LIMIT的值设置成1,这样可以保证只要有丢帧,就会有上面的log输出来。

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static { try { Field field = Choreographer.class.getDeclaredField("SKIPPED_FRAME_WARNING_LIMIT"); field.setAccessible(true); field.set(Choreographer.class,1); } catch (Throwable e) { e.printStackTrace(); } }

注意,这个方案是 API 16 以上才支持。Choreographer就是一个消息处理器,根据vsync 信号 来计算frame,而计算frame的方式就是处理三种回调,包括事件回调、动画回调、绘制回调。这三种事件在消息输入、加入动画、准备绘图layout 等动作时均会发给Choreographer。一句话,我们只要捕获这个log提取出skippedFrames 就可以知道界面是否卡顿。

三、如何检测

采用上面的方式就可以在App内部观测当前App的流畅度了。并且在丢帧的地方打印,就可以知道丢帧的大概原因,大概位置,定位代码问题。

在Choreographer中有个回调接口,FrameCallback。

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public interface FrameCallback { //当新的一帧被绘制的时候被调用。 public void doFrame(long frameTimeNanos); }

根据上面的代码,重写doFrame方法,所以照葫芦画瓢,自定义FrameCallback。我们可以在每一帧被渲染的时候记录下它开始渲染的时间,这样在下一帧被处理时,判断上一帧在渲染过程中是否出现掉帧。

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public class SMFrameCallback implements Choreographer.FrameCallback { public static SMFrameCallback sInstance; private String TAG="SMFrameCallback"; public static final float deviceRefreshRateMs=16.6f; public static long lastFrameTimeNanos=0;//纳秒为单位 public static long currentFrameTimeNanos=0; public void start() { Choreographer.getInstance().postFrameCallback(SMFrameCallback.getInstance()); } public static SMFrameCallback getInstance() { if (sInstance == null) { sInstance = new SMFrameCallback(); } return sInstance; } @Override public void doFrame(long frameTimeNanos) { if(lastFrameTimeNanos==0){ lastFrameTimeNanos=frameTimeNanos; Choreographer.getInstance().postFrameCallback(this); return; } currentFrameTimeNanos=frameTimeNanos; float value=(currentFrameTimeNanos-lastFrameTimeNanos)/1000000.0f; final int skipFrameCount = skipFrameCount(lastFrameTimeNanos, currentFrameTimeNanos, deviceRefreshRateMs); Log.e(TAG,"两次绘制时间间隔value="+value+" frameTimeNanos="+frameTimeNanos+" currentFrameTimeNanos="+currentFrameTimeNanos+" skipFrameCount="+skipFrameCount+""); lastFrameTimeNanos=currentFrameTimeNanos; Choreographer.getInstance().postFrameCallback(this); } /** * *计算跳过多少帧 * @param start * @param end * @param devicefreshRate * @return */ private int skipFrameCount(long start,long end,float devicefreshRate){ int count =0; long diffNs=end-start; long diffMs = Math.round(diffNs / 1000000.0f); long dev=Math.round(devicefreshRate); if(diffMs>dev){ long skipCount=diffMs/dev; count=(int)skipCount; } return count; } }

在需要检测的Activity中调用 SMFrameCallback.getInstance().start()即可。一般优化一下,可以在BaseActivity去调用或者Activitylifecyclecallbacks中去调用.
正常情况下输出的日志是:

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02-07 20:18:52.605 6683-6683/zhangwan.wj.com.choreographertest E/SMFrameCallback: 两次绘制时间间隔value=16.666666 frameTimeNanos=6996166386820 currentFrameTimeNanos=6996166386820 skipFrameCount=0 02-07 20:18:52.621 6683-6683/zhangwan.wj.com.choreographertest E/SMFrameCallback: 两次绘制时间间隔value=16.666666 frameTimeNanos=6996183053486 currentFrameTimeNanos=6996183053486 skipFrameCount=0 02-07 20:18:52.637 6683-6683/zhangwan.wj.com.choreographertest E/SMFrameCallback: 两次绘制时间间隔value=16.666666 frameTimeNanos=6996199720152 currentFrameTimeNanos=6996199720152 skipFrameCount=0 02-07 20:18:52.657 6683-6683/zhangwan.wj.com.choreographertest E/SMFrameCallback: 两次绘制时间间隔value=16.666666 frameTimeNanos=6996216386818 currentFrameTimeNanos=6996216386818 skipFrameCount=0 02-07 20:18:52.673 6683-6683/zhangwan.wj.com.choreographertest E/SMFrameCallback: 两次绘制时间间隔value=16.666666 frameTimeNanos=6996233053484 currentFrameTimeNanos=6996233053484 skipFrameCount=0 02-07 20:18:52.689 6683-6683/zhangwan.wj.com.choreographertest E/SMFrameCallback: 两次绘制时间间隔value=16.666666 frameTimeNanos=6996249720150 currentFrameTimeNanos=6996249720150 skipFrameCount=0

有跳帧的时候输出的日志是

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02-07 20:21:53.909 9530-9530/zhangwan.wj.com.choreographertest E/SMFrameCallback: 两次绘制时间间隔value=16.666666 frameTimeNanos=7177466379568 currentFrameTimeNanos=7177466379568 skipFrameCount=0 02-07 20:21:53.925 9530-9530/zhangwan.wj.com.choreographertest E/SMFrameCallback: 两次绘制时间间隔value=16.666666 frameTimeNanos=7177483046234 currentFrameTimeNanos=7177483046234 skipFrameCount=0 02-07 20:21:54.133 9530-9530/zhangwan.wj.com.choreographertest E/SMFrameCallback: 两次绘制时间间隔value=200.0 frameTimeNanos=7177683046226 currentFrameTimeNanos=7177683046226 skipFrameCount=11 02-07 20:21:54.745 9530-9530/zhangwan.wj.com.choreographertest E/SMFrameCallback: 两次绘制时间间隔value=616.6666 frameTimeNanos=7178299712868 currentFrameTimeNanos=7178299712868 skipFrameCount=36 02-07 20:21:54.757 9530-9530/zhangwan.wj.com.choreographertest E/SMFrameCallback: 两次绘制时间间隔value=16.666666 frameTimeNanos=7178316379534 currentFrameTimeNanos=7178316379534 skipFrameCount=0 02-07 20:21:54.773 9530-9530/zhangwan.wj.com.choreographertest E/SMFrameCallback: 两次绘制时间间隔value=16.666666 frameTimeNanos=7178333046200 currentFrameTimeNanos=7178333046200 skipFrameCount=0 02-07 20:21:54.789 9530-9530/zhangwan.wj.com.choreographertest E/SMFrameCallback: 两次绘制时间间隔value=16.666666 frameTimeNanos=7178349712866 currentFrameTimeNanos=7178349712866 skipFrameCount=0

看到两次绘制的时间间隔相差616.6666毫秒,跳过了36帧,这个卡顿用户是能够明显感知的。

Please accept mybest wishes for your happiness and success !

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