使用NSURLSessionDownloadTask下载时图像不显示

// 创建NSURLSession实例
let session = URLSession(configuration: URLSessionConfiguration.default)

// 创建下载任务
let downloadTask = session.downloadTask(with: imageURL) { (location, response, error) in
    // 检查下载是否成功
    guard let location = location, error == nil else {
        print("下载失败: \(error?.localizedDescription ?? "")")
        return
    }
    
    do {
        // 将临时文件移动到合适的位置
        let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
        let destinationURL = documentsURL.appendingPathComponent("downloadedImage.jpg")
        try FileManager.default.moveItem(at: location, to: destinationURL)
        
        // 在主线程上更新UI
        DispatchQueue.main.async {
            // 创建UIImage对象并将其设置为UIImageView的image属性
            let image = UIImage(contentsOfFile: destinationURL.path)
            imageView.image = image
        }
    } catch {
        print("文件移动失败: \(error.localizedDescription)")
    }
}

// 启动下载任务
downloadTask.resume()