Android 如何优雅的实现App 前后台状态变化通知

原文链接:Coobox 之 App 前后台状态变化通知

如何定义前后台

• 这里的前后台不是 Linux 进程的前后台(Foreground, Backgroud)
• App 前台状态指的是 当用户可以肉眼可见 App 的界面(Activity)，否则为 App 后台状态

如何实现

• 定义一个当前进程的 Activity数量变量，如activityCount, Int类型
• 当进程中的 Activity 执行到 onStart 方法，执行activityCount++
• 当进程中的 Activity 执行到 onStop 方法，执行activityCount--
• 当activityCount 为 0, 则表示 App 在后台状态，否则为前台状态

使用简介

监听 前后台 状态变化

AppStateHelper.addListener(object: OnAppStateChangedListener {
    override fun onAppStateChanged(state: AppStateHelper.Message, activity: Activity) {
      Log.i("AppStateHelper", "onAppStateChanged message=$state;activity=$activity")
    }
})

手动触发调用

class AppStateTestFragment : TestableFragment(), OnAppStateChangedListener {
    override fun addTestItems() {
    }

    fun setupAppStateHelper(application: Application) {
        application.registerActivityLifecycleCallbacks(object: ActivityLifecycleCallbacksImpl() {
            override fun onActivityStarted(activity: Activity) {
                super.onActivityStarted(activity)
                AppStateHelper.activityStarting(activity)
            }

            override fun onActivityStopped(activity: Activity) {
                super.onActivityStopped(activity)
                AppStateHelper.activityStopping(activity)
            }
        })
    }
}

查询前后台状态

// App是否为前台状态
val isForeground = AppStateHelper.isForeground

// App 是否为后台状态
val isBackground = AppStateHelper.isBackground

// App 的状态
val appState = AppStateHelper.state

实现代码

package com.secoo.coobox.library.lifecycle

import android.app.Activity


object AppStateHelper {
    private var activityCount = 0
    private val listeners = mutableListOf<OnAppStateChangedListener>()

    /**
     * 判断 App 当前是否为前台可见状态
     */
    val isForeground: Boolean
        get() = activityCount != 0

    /**
     * 判断 App 当前是否为后台不可见状态
     */
    val isBackground: Boolean
        get() = activityCount == 0


    enum class Message {
        BACKGROUNDED, FOREGROUNDED
    }

    /**
     * 返回当前的App状态
     * @return
     */
    val state: Message
        get() = if (isForeground) {
            Message.FOREGROUNDED
        } else {
            Message.BACKGROUNDED
        }

    /**
     * Activity 执行到 onStart 时调用，需主动调用
     */
    fun activityStarting(activity: Activity): Boolean {
        var ret = false
        if (activityCount == 0) {
            onForeground(activity)
            ret = true
        }
        activityCount++
        return ret
    }

    /**
     * Activity 执行到 onStop 时调用，需主动调用
     * */
    @Synchronized
    fun activityStopping(activity: Activity): Boolean {
        activityCount--
        if (activityCount == 0) {
            onBackground(activity)
            return true
        }
        return false
    }

    fun addListener(listener: OnAppStateChangedListener) {
        listeners.add(listener)
    }

    fun removeListener(listener: OnAppStateChangedListener) {
        listeners.remove(listener)
    }

    private fun onBackground(activity: Activity) {
        listeners.forEach {
            it.onAppStateChanged(Message.BACKGROUNDED, activity)
        }
    }

    private fun onForeground(activity: Activity) {
        listeners.forEach {
            it.onAppStateChanged(Message.FOREGROUNDED, activity)
        }
    }

}

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如何引入

• AppStateHelper已经包含进入 CooBox, 快速集成 Coobox https://github.com/secoo-android/coobox