如何判斷APP在前臺還是后臺？

作者：Reathin 2024-01-22 08:21:46

當我們不管是點擊Back鍵還是Home鍵都會回調到onStop方法，我們在onStart和onStop中分別對mCount值做了加減，這樣我們可以通過該數值來判斷當前App是前臺還是后臺。

如何判斷一個APP在前臺還是后臺？可以通過RunningTasks，RunningProcess 以及ActivityLifecycleCallback判定。

RunningTasks方式

注意：getRunningTask方法在5.0以上已經被廢棄，只能返回自己和系統的一些不敏感的task，不再返回其他應用的task，用此方法來判斷自身App是否處于后臺是有效的，但是無法判斷其他應用是否處于前臺。

private fun getTopApplication() {

    //首先獲取到ActivityManager
    val activityManager = getSystemService(Context.ACTIVITY_SERVICE) as ActivityManager

    if (activityManager.getRunningTasks(1) == null){
        Log.e(TAG, "getForegroundActivity: ")
        return
    }

    var runningTaskInfo = activityManager.getRunningTasks(1)[0]
    if (runningTaskInfo == null) {
        Log.e(TAG, "runningTaskInfo is null")
        return
    }

    runningTaskInfo.topActivity?.let {
        Log.e(TAG, "top application is ${it.packageName}")
    }
}

RunningProcess方式

注意：RunningProcess方法在5.0以上已經被廢棄，例如，在聊天類型的App中，大部分時間需要常駐后臺來不間斷地獲取服務器的消息，就必須把Service設置成START_STICKY，kill后會被重啟（等待5s左右）來保證Service常駐后臺。如果Service設置了這個屬性，這個App的進程就可以判斷為前臺。

appProcess.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND

private fun isAppForeground(): Boolean {
    val activityManager = getSystemService(Context.ACTIVITY_SERVICE) as ActivityManager
    var runningAppProcesses = activityManager.runningAppProcesses

    if (runningAppProcesses == null) {
        Log.e(TAG, "runningAppProcesses is null")
        return false
    }

    runningAppProcesses.forEach {
        if (it.processName == packageName && (it.importance == ActivityManager.RunningAppProcessInfo.IMPORTANCE_FOREGROUND)) {
            return true
        }
    }
    return false
}

ActivityLifecycleCallbacks方式

class MyActivityLifecycleCallbacks(
    var onActivityCreatedAction: ((Activity, Bundle?) -> Unit)? = null,
    var onActivityStartedAction: ((Activity) -> Unit)? = null,
    var onActivityResumedAction: ((Activity) -> Unit)? = null,
    var onActivityPausedAction: ((Activity) -> Unit)? = null,
    var onActivityStoppedAction: ((Activity) -> Unit)? = null,
    var onActivitySaveInstanceStateAction: ((Activity, Bundle) -> Unit)? = null,
    var onActivityDestroyedAction: ((Activity) -> Unit)? = null

) : Application.ActivityLifecycleCallbacks {

    private var mCount=0
    override fun onActivityCreated(activity: Activity, savedInstanceState: Bundle?) {
        onActivityCreatedAction?.invoke(activity, savedInstanceState)
    }

    override fun onActivityStarted(activity: Activity) {
        mCount++
        onActivityStartedAction?.invoke(activity)
    }

    override fun onActivityResumed(activity: Activity) {
        onActivityResumedAction?.invoke(activity)
    }

    override fun onActivityPaused(activity: Activity) {
        onActivityPausedAction?.invoke(activity)
    }

    override fun onActivityStopped(activity: Activity) {
        mCount--
        onActivityStoppedAction?.invoke(activity)
    }

    override fun onActivitySaveInstanceState(activity: Activity, outState: Bundle) {
        onActivitySaveInstanceStateAction?.invoke(activity, outState)
    }

    override fun onActivityDestroyed(activity: Activity) {
        onActivityDestroyedAction?.invoke(activity)
    }

    /**
     * 這里我們把mCount的實際數值返回回去
     */
    fun getCount():Int = mCount
}

這里我們對ActivityLifecycleCallbacks的實現類做了一層封裝，利用Kotlin的高階函數，當我們需要去實現那個聲明周期的回調的時候，就通過高階函數來提供回調處理，否則默認不做任何處理。然后我們在Application的onCreate中進行注冊:

class LifeApplication : Application() {

    private val TAG = "LifeApplication"

    private val mActivityLifecycleCallbacks by lazy {
        MyActivityLifecycleCallbacks(
            onActivityCreatedAction = { activit, bundle ->
            Log.e(TAG, "onCreate: ")
        },
        onActivityStoppedAction = { activity ->
            Log.e(TAG, "onStop ")
        },
        onActivityDestroyedAction = { activity ->
            Log.e(TAG, "onDestroy")
        })
    }

    override fun onCreate() {
        super.onCreate()
        instance = this
        //注冊生命周期回調事件
        registerActivityLifecycleCallbacks(mActivityLifecycleCallbacks)
    }

    /**
     * 用于判斷當前進程是否處于前臺
     */
    fun isForegroundMethod(): Boolean = mActivityLifecycleCallbacks.getCount() > 0

    companion object{
        private var instance :LifeApplication?= null
        fun getInstance () = instance!!
    }

責任編輯：武曉燕來源：沐雨花飛蝶