能力
JankStats 库可帮助您跟踪和分析应用程序中的性能问题。Jank 是指渲染时间过长的应用程序帧，JankStats 库提供有关应用程序卡顿统计信息的报告。
JankStats 建立在现有 Android 平台功能之上，包括 Android 7（API 级别 24）及更高版本上的FrameMetrics API或早期版本上的OnPreDrawListener 。这些机制可以帮助应用程序跟踪完成帧需要多长时间。
用法
添加依赖
implementation "androidx.metrics:metrics-performance:1.0.0-alpha03"初始化
class JankLoggingActivity : AppCompatActivity() {private lateinit var jankStats: JankStatsoverride fun onCreate(savedInstanceState: Bundle?) {super.onCreate(savedInstanceState)// ...// metrics state holder can be retrieved regardless of JankStats initializationval metricsStateHolder = PerformanceMetricsState.getHolderForHierarchy(binding.root)// 初始化JankStats jankFrameListener在用于将信息从平台传递到内部 JankStats 的同一线程上调用jankStats = JankStats.createAndTrack(window, jankFrameListener)//这个因子乘以当前的刷新率来计算帧持续时间，超过这个时间的帧被认为有jank，默认是2jankStats.jankHeuristicMultiplier = 3.0f;// 添加状态metricsStateHolder.state?.putState("Activity", javaClass.simpleName)// ...}JankLoggingActivity.kt
开启和关闭控制
override fun onResume() {super.onResume()jankStats.isTrackingEnabled = true
}override fun onPause() {super.onPause()jankStats.isTrackingEnabled = false
}
反馈异常
private val jankFrameListener = JankStats.OnFrameListener { frameData ->// A real app could do something more interesting, like writing the info to local storage and later on report it.Log.v("JankStatsSample", frameData.toString())
}JankLoggingActivity.kt产物
FrameData(frameStartNanos=36648326900279, frameDurationUiNanos=209972875, frameDurationCpuNanos=211467511, isJank=true, states=[Navigation: Args(null), Destination(com.example.jankstats:id/messageRecycler) label=Message List class=com.example.jankstats.MessageListFragment])
侦听器提供有关对象卡顿的每帧信息 FrameData。这包含有关所请求帧的以下信息：
isjank：一个布尔标志，指示帧中是否发生卡顿。
frameDurationUiNanos：帧的持续时间（以纳秒为单位）。
frameStartNanos：帧开始的时间（以纳秒为单位）。
states：您的应用程序在帧中的状态。
原理
初始化 JankStats：传染当前activity的window和监听器
JankStats.createAndTrack(window, jankFrameListener)
init {val decorView: View? = window.peekDecorView()if (decorView == null) {throw IllegalStateException("window.peekDecorView() is null: " +"JankStats can only be created with a Window that has a non-null DecorView")}//创建holder,用来保存状态holder = PerformanceMetricsState.create(decorView)//根据版本初始化对应的implementation =JankStats，获取帧率的方式不同when {Build.VERSION.SDK_INT >= 31 -> {JankStatsApi31Impl(this, decorView, window)}Build.VERSION.SDK_INT >= 26 -> {JankStatsApi26Impl(this, decorView, window)}Build.VERSION.SDK_INT >= 24 -> {JankStatsApi24Impl(this, decorView, window)}Build.VERSION.SDK_INT >= 22 -> {JankStatsApi22Impl(this, decorView)}Build.VERSION.SDK_INT >= 16 -> {JankStatsApi16Impl(this, decorView)}else -> {JankStatsBaseImpl(this)}}//设置监听回调implementation.setupFrameTimer(true)}>= api16 setupFrameTimer
//创建ViewTreeObserver.OnPreDrawListener添加到viewTreeObserver
//在OnPreDrawListener中获取当前帧开始时间，当前时间，帧预期耗时
//调用OnFrameListenerDelegate的onFrame(开始时间，now - 开始时间，预期时间)方法
//在onFrame中判断是不是jank
override fun setupFrameTimer(enable: Boolean) {val decorView = decorViewRef.get()decorView?.let {if (enable) {//通过ViewTreeObserver.OnPreDrawListene来计算当前帧的耗时 val delegates = decorView.getOrCreateOnPreDrawListenerDelegator()delegates.add(onFrameListenerDelegate)} else {decorView.removeOnPreDrawListenerDelegate(onFrameListenerDelegate)}}}端上注册了jankStats.logFrameData监听
private val onFrameListenerDelegate = object : OnFrameListenerDelegate() {override fun onFrame(startTime: Long, uiDuration: Long, expectedDuration: Long) {jankStats.logFrameData(getFrameData(startTime, uiDuration,(expectedDuration * jankStats.jankHeuristicMultiplier).toLong()))}}internal open fun getFrameData(startTime: Long,uiDuration: Long,expectedDuration: Long): FrameData {metricsStateHolder.state?.getIntervalStates(startTime, startTime + uiDuration,stateInfo)//判断是不是jankval isJank = uiDuration > expectedDurationframeData.update(startTime, uiDuration, isJank)return frameData}
