应用生命周期

源：Android Lifecycle | iOS App Lifecycle

监听应用前后台切换、启动和退出等生命周期事件，是资源管理、数据同步的关键。本文展示如何跨平台监听应用生命周期。

平台差异对比

平台	原生 API	生命周期回调	适用场景
Android	ProcessLifecycleOwner	onCreate、onStart、onStop	全局生命周期监听
iOS	UIApplicationDelegate / SceneDelegate	didBecomeActive、didEnterBackground	应用状态变化
Desktop	-	-	无标准生命周期

expect/actual 实现方案

标准代码块

commonMain

enum class AppState {
    FOREGROUND,
    BACKGROUND
}

interface AppLifecycleObserver {
    fun onAppStateChanged(state: AppState)
}

expect object AppLifecycle {
    fun addObserver(observer: AppLifecycleObserver)
    fun removeObserver(observer: AppLifecycleObserver)
    fun getCurrentState(): AppState
}

androidMain

import androidx.lifecycle.DefaultLifecycleObserver
import androidx.lifecycle.LifecycleOwner
import androidx.lifecycle.ProcessLifecycleOwner

actual object AppLifecycle {
    
    private val observers = mutableSetOf<AppLifecycleObserver>()
    private var currentState = AppState.FOREGROUND
    
    private val lifecycleObserver = object : DefaultLifecycleObserver {
        override fun onStart(owner: LifecycleOwner) {
            currentState = AppState.FOREGROUND
            observers.forEach { it.onAppStateChanged(AppState.FOREGROUND) }
        }
        
        override fun onStop(owner: LifecycleOwner) {
            currentState = AppState.BACKGROUND
            observers.forEach { it.onAppStateChanged(AppState.BACKGROUND) }
        }
    }
    
    fun init() {
        ProcessLifecycleOwner.get().lifecycle.addObserver(lifecycleObserver)
    }
    
    actual fun addObserver(observer: AppLifecycleObserver) {
        observers.add(observer)
    }
    
    actual fun removeObserver(observer: AppLifecycleObserver) {
        observers.remove(observer)
    }
    
    actual fun getCurrentState(): AppState {
        return currentState
    }
}

iosMain

import platform.Foundation.NSNotificationCenter
import platform.UIKit.*

actual object AppLifecycle {
    
    private val observers = mutableSetOf<AppLifecycleObserver>()
    private var currentState = AppState.FOREGROUND
    
    fun init() {
        val center = NSNotificationCenter.defaultCenter
        
        center.addObserverForName(
            UIApplicationDidBecomeActiveNotification,
            null,
            null
        ) { _ ->
            currentState = AppState.FOREGROUND
            observers.forEach { it.onAppStateChanged(AppState.FOREGROUND) }
        }
        
        center.addObserverForName(
            UIApplicationDidEnterBackgroundNotification,
            null,
            null
        ) { _ ->
            currentState = AppState.BACKGROUND
            observers.forEach { it.onAppStateChanged(AppState.BACKGROUND) }
        }
    }
    
    actual fun addObserver(observer: AppLifecycleObserver) {
        observers.add(observer)
    }
    
    actual fun removeObserver(observer: AppLifecycleObserver) {
        observers.remove(observer)
    }
    
    actual fun getCurrentState(): AppState {
        return currentState
    }
}

jvmMain

actual object AppLifecycle {
    actual fun addObserver(observer: AppLifecycleObserver) {}
    actual fun removeObserver(observer: AppLifecycleObserver) {}
    actual fun getCurrentState(): AppState = AppState.FOREGROUND
}

依赖补充

Android Lifecycle

Kotlin DSL

kotlin {
    sourceSets {
        androidMain.dependencies {
            implementation("androidx.lifecycle:lifecycle-process:2.7.0")
        }
    }
}

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