如何使用Swift 4显示本地时区日落时间并替换Label文本

Hey there! Let's walk through how to grab the local timezone's sunset time and display it in a UILabel using Swift 4. Here's everything you need to know, step by step:

First, you'll need the CoreLocation framework—sunset time depends on geographic coordinates (not just timezone alone). Import it in your view controller, and don't forget to add permission descriptions to your Info.plist:

• In your Info.plist, add the key NSLocationWhenInUseUsageDescription with a value like "We need your location to calculate local sunset time." This tells users why you're requesting location access.

Here's a complete view controller example that handles permissions, fetches the current location, calculates sunset time, and updates your label:

import UIKit
import CoreLocation

class ViewController: UIViewController, CLLocationManagerDelegate {
    // Connect this outlet to your Text Label in Interface Builder
    @IBOutlet weak var sunsetTimeLabel: UILabel!
    private let locationManager = CLLocationManager()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        setupLocationManager()
    }
    
    private func setupLocationManager() {
        locationManager.delegate = self
        // We don't need ultra-precise location for sunset calculations
        locationManager.desiredAccuracy = kCLLocationAccuracyThreeKilometers
        // Request permission to access location while the app is in use
        locationManager.requestWhenInUseAuthorization()
        locationManager.startUpdatingLocation()
    }
    
    // Triggered when we get a valid location update
    func locationManager(_ manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
        guard let currentLocation = locations.last else { return }
        // Stop updating location once we have what we need to save battery
        locationManager.stopUpdatingLocation()
        
        // Calculate and display the sunset time
        fetchAndDisplaySunsetTime(for: currentLocation)
    }
    
    // Handle changes to location permission status
    func locationManager(_ manager: CLLocationManager, didChangeAuthorization status: CLAuthorizationStatus) {
        switch status {
        case .authorizedWhenInUse, .authorizedAlways:
            locationManager.startUpdatingLocation()
        case .denied, .restricted:
            sunsetTimeLabel.text = "Location access denied — can't show sunset time"
        default:
            break
        }
    }
    
    // Handle location fetch errors
    func locationManager(_ manager: CLLocationManager, didFailWithError error: Error) {
        sunsetTimeLabel.text = "Failed to get location: \(error.localizedDescription)"
    }
    
    private func fetchAndDisplaySunsetTime(for location: CLLocation) {
        let currentDate = Date()
        let localTimeZone = TimeZone.current
        let calendar = Calendar.current
        
        // Calculate sunset time (iOS 10+ API)
        guard let sunsetDate = calendar.sunsetTime(for: location, date: currentDate, timeZone: localTimeZone) else {
            sunsetTimeLabel.text = "Couldn't calculate sunset time"
            return
        }
        
        // Format the time into a user-friendly string
        let dateFormatter = DateFormatter()
        dateFormatter.timeZone = localTimeZone
        // Use "HH:mm" for 24-hour format, or "h:mm a" for 12-hour with AM/PM
        dateFormatter.dateFormat = "h:mm a"
        let formattedSunset = dateFormatter.string(from: sunsetDate)
        
        // Update your label with the sunset time
        sunsetTimeLabel.text = "Today's Sunset: \(formattedSunset)"
    }
}

• If you need sunset time for a specific city (not the user's current location), create a fixed CLLocation with that city's coordinates:

  // Example: London coordinates
  let londonLocation = CLLocation(latitude: 51.5074, longitude: -0.1278)
  fetchAndDisplaySunsetTime(for: londonLocation)
  

• Adjust the dateFormat in DateFormatter to match your preferred display style (e.g., "EEEE, MMM d, h:mm a" for full date + time).

• The sunsetTime(for:date:timeZone:) API works on iOS 10 and later. If you need to support older versions, you'll have to implement manual sunset calculation logic (which is more complex).
• Always handle permission denials gracefully so users understand why the feature isn't working.

内容的提问来源于stack exchange，提问作者Shahid Miah