iOS 应用程序未激活时后台下载

在iOS应用程序中，后台下载是一项非常重要且常见的功能。它允许应用程序在未激活状态下继续进行文件下载，无论是在用户退出应用程序、锁定设备还是切换到其他应用程序时。这对于那些需要下载大量数据或需要在后台进行长时间操作的应用程序来说尤为重要。本文将介绍如何在iOS应用程序中实现后台下载功能，并提供一些代码示例。

swift
let url = URL(string: "http://example.com/file.zip")
let config = URLSessionConfiguration.background(withIdentifier: "com.example.backgroundDownload")
let session = URLSession(configuration: config, delegate: self, delegateQueue: OperationQueue.main)
let downloadTask = session.downloadTask(with: url!)
downloadTask.resume()

swift
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
    // 下载完成后的处理逻辑
}
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
    // 下载任务完成或出现错误的处理逻辑
}
func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {
    // 后台下载任务完成后的处理逻辑
}

swift
import UIKit
class ViewController: UIViewController, URLSessionDelegate, URLSessionDownloadDelegate {
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 开始后台下载
        startBackgroundDownload()
    }
    
    func startBackgroundDownload() {
        let url = URL(string: "http://example.com/file.zip")
        let config = URLSessionConfiguration.background(withIdentifier: "com.example.backgroundDownload")
        let session = URLSession(configuration: config, delegate: self, delegateQueue: OperationQueue.main)
        
        let downloadTask = session.downloadTask(with: url!)
        downloadTask.resume()
    }
    
    // 下载完成后的处理逻辑
    func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
        // 将下载的文件移动到沙盒中的指定路径
        let documentsPath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0] as NSString
        let destinationPath = documentsPath.appendingPathComponent("file.zip")
        
        let fileManager = FileManager.default
        try? fileManager.moveItem(at: location, to: URL(fileURLWithPath: destinationPath))
        
        // 下载完成后的提示
        let alertController = UIAlertController(title: "下载完成", message: "文件已保存到\(destinationPath)", preferredStyle: .alert)
        let okAction = UIAlertAction(title: "确定", style: .default, handler: nil)
        alertController.addAction(okAction)
        present(alertController, animated: true, completion: nil)
    }
    
    // 下载任务完成或出现错误的处理逻辑
    func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
        if let error = error {
            print("下载任务出现错误：\(error.localizedDescription)")
        } else {
            print("下载任务完成")
        }
    }
    
    // 后台下载任务完成后的处理逻辑
    func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {
        if let appDelegate = UIApplication.shared.delegate as? AppDelegate,
           let completionHandler = appDelegate.backgroundSessionCompletionHandler {
            appDelegate.backgroundSessionCompletionHandler = nil
            completionHandler()
        }
    }
}