其实主要就是通过Application的ActivityLifecycleCallbacks回调, 判断当前所有Activity的生命周期.

整个核心代码如下:

object RBackground { const val CREATE = "onActivityCreated" const val STARTED = "onActivityStarted" const val RESUMED = "onActivityResumed" const val PAUSED = "onActivityPaused" const val STOPPED = "onActivityStopped" const val SAVE = "onActivitySaveInstanceState" /** class_name|state */ val stack = SparseArray<String>() private val observers = mutableListOf<OnBackgroundObserver>() /**主线程回调*/ val lifecycleCallbacks = object : Application.ActivityLifecycleCallbacks { override fun onActivityCreated(activity: Activity, savedInstanceState: Bundle?) { pushItem(activity.hashCode(), activity.javaClass.name, CREATE) } override fun onActivityStarted(activity: Activity) { changeItem(activity.hashCode(), activity.javaClass.name, STARTED) } override fun onActivityResumed(activity: Activity) { changeItem(activity.hashCode(), activity.javaClass.name, RESUMED) } override fun onActivityPaused(activity: Activity) { if (activity.isFinishing) { } else { changeItem(activity.hashCode(), activity.javaClass.name, PAUSED) } } override fun onActivityStopped(activity: Activity) { if (activity.isFinishing) { } else { changeItem(activity.hashCode(), activity.javaClass.name, STOPPED) } } override fun onActivityDestroyed(activity: Activity) { removeItem(activity.hashCode(), activity.javaClass.name) } override fun onActivitySaveInstanceState(activity: Activity, outState: Bundle?) { changeItem(activity.hashCode(), activity.javaClass.name, SAVE) } } private fun pushItem(code: Int, className: String, state: String) { val item = "$className|$state" stack.put(code, item) observers.forEach { it.onActivityChanged(stack, isBackground()) } } private fun changeItem(code: Int, className: String, state: String) { pushItem(code, className, state) } private fun removeItem(code: Int, className: String) { stack.remove(code) observers.forEach { it.onActivityChanged(stack, isBackground()) } } fun init(application: Application, observer: OnBackgroundObserver? = null) { application.registerActivityLifecycleCallbacks(lifecycleCallbacks) observer?.let { registerObserver(it) } } fun isBackground(): Boolean { var result = stack.size() != 0 for (i in 0 until stack.size()) { val value = stack.get(stack.keyAt(i)) if (value.endsWith(STOPPED)) { } else { result = false break } } return result } fun registerObserver(observer: OnBackgroundObserver) { if (!observers.contains(observer)) { observers.add(observer) } } fun unregisterObserver(observer: OnBackgroundObserver) { observers.remove(observer) } } interface OnBackgroundObserver { fun onActivityChanged(stack: SparseArray<String>, background: Boolean) }

使用方法:

RBackground.init(this, object : OnBackgroundObserver { override fun onActivityChanged(stack: SparseArray<String>, background: Boolean) { L.d("$stack") if (background) { //切换到后台 Tip.tip("您已切换至后台") } } })

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