Suspended — iOS 后台应用冻结是什么

import UIKit

@main
class AppDelegate: UIResponder, UIApplicationDelegate {

    // 进入 Suspended 前的最后保证调用
    func applicationDidEnterBackground(_ application: UIApplication) {
        // 保存所有需要在内存卸载后保留的数据
        savePersistentState()
        saveNavigationStack()

        // 如果需要，请求额外时间
        let task = application.beginBackgroundTask {
            application.endBackgroundTask(task)
        }
    }

    // 从 Suspended 返回 — 热启动
    func applicationWillEnterForeground(_ application: UIApplication) {
        // 应用程序已在 Suspended 状态，恢复运行
        print("从 Suspended 或 Background 返回")
    }

    // 内存卸载后的完全恢复
    func application(
        _ application: UIApplication,
        didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
    ) -> Bool {
        // 如果这是从 Suspended 卸载后的冷启动 —
        // 恢复状态恢复
        return true
    }

    private func savePersistentState() {
        UserDefaults.standard.set(Date(), forKey: "lastActiveDate")
    }

    private func saveNavigationStack() {
        guard let rootVC = window?.rootViewController else { return }
        // 保存当前导航堆栈
        if let navController = rootVC as? UINavigationController {
            let vcClasses = navController.viewControllers.map { type(of: $0) }
            UserDefaults.standard.set(vcClasses.map { NSStringFromClass($0) }, forKey: "navStack")
        }
    }
}

// SavedStateHandle — Android 上避免进程终止的救星
class CheckoutViewModel(
    private val savedStateHandle: SavedStateHandle
) : ViewModel() {

    // 即使在应用冻结后也能保留的状态
    var currentStep: MutableLiveData<Int> =
        savedStateHandle.getLiveData("checkout_step", 1)

    var cartItems: MutableLiveData<List<CartItem>> =
        savedStateHandle.getLiveData("cart_items", emptyList())

    fun proceedToNextStep() {
        currentStep.value = (currentStep.value ?: 0) + 1
    }

    fun addToCart(item: CartItem) {
        val updatedList = (cartItems.value ?: emptyList()) + item
        cartItems.value = updatedList
        savedStateHandle["cart_items"] = updatedList
    }
}

// 在 onStop 中保存以应对应用冻结
class MainActivity : AppCompatActivity() {

    override fun onStop() {
        super.onStop()
        // 保存需要在冻结后保留的数据
        saveDraftData()
        // 释放在冻结状态下不需要的资源
        releaseHeavyResources()
        // 警告应用程序将被冻结
        // （调试日志记录）
        Log.d("生命周期", "Activity 已停止 — 可能的应用冻结")
    }
}

import UIKit

class DetailViewController: UIViewController {

    var itemID: String = ""
    var scrollPosition: CGPoint = .zero

    override func viewDidLoad() {
        super.viewDidLoad()
        restorationIdentifier = "DetailViewController"
        restorationClass = type(of: self)
    }

    override func encodeRestorableState(with coder: NSCoder) {
        super.encodeRestorableState(with: coder)
        coder.encode(itemID, forKey: "itemID")
        coder.encode(scrollPosition, forKey: "scrollPosition")
    }

    override func decodeRestorableState(with coder: NSCoder) {
        super.decodeRestorableState(with: coder)
        if let savedID = coder.decodeObject(forKey: "itemID") as? String {
            itemID = savedID
            loadItem()
        }
        if let savedPosition = coder.decodeCGPoint(forKey: "scrollPosition") {
            scrollPosition = savedPosition
            // 数据加载后恢复位置
        }
    }
}

// AppDelegate — 激活状态恢复
func application(
    _ application: UIApplication,
    shouldSaveSecureApplicationState coder: NSCoder
) -> Bool {
    return true
}

func application(
    _ application: UIApplication,
    shouldRestoreSecureApplicationState coder: NSCoder
) -> Bool {
    return true
}

import UIKit

// 检查：应用程序是否已从内存中卸载？
func application(
    _ application: UIApplication,
    didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?
) -> Bool {
    // 检查是否有保存的状态
    if UserDefaults.standard.object(forKey: "navStack") != nil {
        // 应用程序已从 Suspended 卸载
        // 需要恢复状态
        restoreNavigationStack()
    } else {
        // 从 Not Running 的纯冷启动
        showOnboardingIfNeeded()
    }
    return true
}

private func restoreNavigationStack() {
    guard let savedStack = UserDefaults.standard.array(forKey: "navStack") as? [String],
          let navController = window?.rootViewController as? UINavigationController
    else { return }

    for vcClassName in savedStack {
        if let vcClass = NSClassFromString(vcClassName) as? UIViewController.Type {
            let vc = vcClass.init()
            navController.pushViewController(vc, animated: false)
        }
    }
}