Swift中如何在特定时间执行代码？日夜模式切换需求咨询

Got it, let's work through this problem. You need to switch day/night mode at 6 AM and 6 PM only when your app is in the foreground, no background execution required, and make sure other app functions keep running smoothly. Here's a clean, native Swift approach that fits all your requirements:

Core Concept #

We'll use a combination of:

• NotificationCenter to listen for app foreground/background state changes
• Calendar to calculate the exact next trigger time (6 AM or 6 PM)
• Timer to fire the mode toggle at the right time (only when the app is active)

This way, we don't waste resources in the background, and we ensure the timer only runs when the app is in use.

Step 1: Create a Mode Toggle Manager #

We'll encapsulate all logic in a dedicated class to keep your code organized and avoid cluttering view controllers or app delegates.

import UIKit

class ModeToggleManager {
    static let shared = ModeToggleManager()
    private var toggleTimer: Timer?
    
    private init() {
        // Listen for app state changes
        NotificationCenter.default.addObserver(self, selector: #selector(appDidBecomeActive), name: UIApplication.didBecomeActiveNotification, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(appWillResignActive), name: UIApplication.willResignActiveNotification, object: nil)
    }
    
    @objc private func appDidBecomeActive() {
        // When app comes to foreground, start or reset the timer
        scheduleNextToggle()
    }
    
    @objc private func appWillResignActive() {
        // When app goes to background, invalidate the timer to save resources
        toggleTimer?.invalidate()
        toggleTimer = nil
    }
    
    private func scheduleNextToggle() {
        // Invalidate existing timer first
        toggleTimer?.invalidate()
        
        let calendar = Calendar.current
        let now = Date()
        
        // Calculate next 6 AM and 6 PM
        guard let nextMorning6 = calendar.nextDate(after: now, matching: DateComponents(hour: 6, minute: 0, second: 0), matchingPolicy: .strict),
              let nextEvening6 = calendar.nextDate(after: now, matching: DateComponents(hour: 18, minute: 0, second: 0), matchingPolicy: .strict) else {
            return
        }
        
        // Pick the sooner of the two
        let nextTriggerTime = min(nextMorning6, nextEvening6)
        
        // Check if we've already passed the trigger time (e.g., app opened at 7 AM)
        if nextTriggerTime <= now {
            // Trigger immediately, then schedule the next one
            toggleMode()
            scheduleNextToggle()
            return
        }
        
        // Calculate time interval until next trigger
        let timeInterval = nextTriggerTime.timeIntervalSince(now)
        
        // Schedule the timer
        toggleTimer = Timer.scheduledTimer(withTimeInterval: timeInterval, repeats: false) { [weak self] _ in
            self?.toggleMode()
            // Schedule the next toggle after this one fires
            self?.scheduleNextToggle()
        }
    }
    
    private func toggleMode() {
        // Replace this with your actual day/night mode switching logic
        DispatchQueue.main.async {
            let currentStyle = UIApplication.shared.keyWindow?.overrideUserInterfaceStyle
            UIApplication.shared.keyWindow?.overrideUserInterfaceStyle = currentStyle == .dark ? .light : .dark
            
            // Optional: Post a notification if other parts of the app need to react to the mode change
            NotificationCenter.default.post(name: NSNotification.Name("ModeDidToggle"), object: nil)
        }
    }
}

Step 2: Initialize the Manager #

You just need to initialize the manager once when your app launches. Add this to your SceneDelegate (for iOS 13+) or AppDelegate:

// In SceneDelegate.swift
func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
    // Initialize the toggle manager
    _ = ModeToggleManager.shared
    // ... rest of your code
}

Key Notes #

• Foreground-only execution: The timer is only active when the app is in the foreground. We invalidate it as soon as the app moves to the background, so no background resources are used.
• Timezone awareness: Uses Calendar.current, which respects the user's device timezone, so triggers happen at local 6 AM/PM.
• Non-intrusive: The manager is self-contained, so it won't interfere with other app functionality. If you need other parts of the app to react to mode changes, use the optional notification we added.
• Edge case handling: If the app is opened after a trigger time (e.g., 7 AM), it will immediately toggle the mode and schedule the next trigger (6 PM that day).

Troubleshooting Tips #

• If the toggle doesn't fire, double-check that the manager is initialized correctly at app launch.
• Ensure your mode switching logic runs on the main thread (we added DispatchQueue.main.async in toggleMode() to handle this, since UI changes must happen on the main thread).
• Test timezone changes to make sure triggers adjust correctly with the user's location.

内容的提问来源于stack exchange，提问作者Bubba