Alamofire是一个纯粹的网络库，关于UI的部分有另外的封装，比如AlamofireImage
和AlamofireNetworkActivityIndicator
一、URLSession
步骤
- 创建session会话
- 根据url创建dataTask
- 取消挂起状态，resume()
URLSession.shared.dataTask(with: url) { (data, response, error) in
if error == nil {
print("请求成功 \(String(describing: response))")
}
}.resume()
URLSession的三种configuration
let configuration1 = URLSessionConfiguration.default
print("configuration1沙盒大小:\(String(describing: configuration1.urlCache?.diskCapacity))")
print("configuration1内存大小:\(String(describing: configuration1.urlCache?.memoryCapacity))")
let configuration2 = URLSessionConfiguration.ephemeral
print("configuration2沙盒大小:\(String(describing: configuration2.urlCache?.diskCapacity))")
print("configuration2内存大小:\(String(describing: configuration2.urlCache?.memoryCapacity))")
/*
打印结果：
configuration1沙盒大小:Optional(10000000)
configuration1内存大小:Optional(512000)
configuration2沙盒大小:Optional(0)
configuration2内存大小:Optional(512000)
*/
.default，默认模式，系统会创建一个持久化的缓存并在用户钥匙串中存储证书
.ephemeral，系统没有持久化存储，所有内容的生命周期都与session相同，当session无效时所有内容自动释放
.background(withIdentifier identifier: String)，创建一个可以在后台甚至APP已经关闭的时候仍然在传输数据的会话，默认是挂起状态
- 实现后台下载与进度打印
- 创建session会话
- 根据url创建dataTask
- 取消挂起状态，resume()
let configuration3 = URLSessionConfiguration.background(withIdentifier: self.createID())
let session = URLSession.init(configuration: configuration3, delegate: self, delegateQueue: OperationQueue.main)
session.downloadTask(with: url).resume()
- 代理回调delegate
//ViewController
extension ViewController:URLSessionDownloadDelegate {
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didFinishDownloadingTo location: URL) {
print("下载完成-\(location)")
let locationPath = location.path
//取得新地址，文件以当前时间的时间戳命名
let documents = NSHomeDirectory() + "/Documents" + self.stringFromNow() + ".mp4"
print("新地址:\(documents)")
//移动文件
let fileManager = FileManager.default
try! fileManager.moveItem(atPath: locationPath, toPath: documents)
}
func urlSession(_ session: URLSession, downloadTask: URLSessionDownloadTask, didWriteData bytesWritten: Int64, totalBytesWritten: Int64, totalBytesExpectedToWrite: Int64) {
print("下载进度:\(totalBytesWritten/totalBytesExpectedToWrite)")
}
}
- 申请后台下载权限，AppDelegate设置回调CompletionHandler
//AppDelegate设置回调
var backgroundSessionCompletionHandler: (() -> Void)?
func application(_ application: UIApplication, handleEventsForBackgroundURLSession identifier: String, completionHandler: @escaping () -> Void) {
self.backgroundSessionCompletionHandler = completionHandler
}
- AppDelegate的回调completionHandler执行
从handleEventsForBackgroundURLSession方法的官方解释（option+方法查看官方解释）中知道
completionHandler
The completion handler to call when you finish processing the events. Calling this completion handler lets the system know that your app’s user interface is updated and a new snapshot can be taken.
因此，在AppDelegate设置的回调completionHandler需要在下载完成后在URLSessionDownloadDelegate执行，告诉系统执行完毕可以回收并刷新UI，避免影响系统运行性能
func urlSessionDidFinishEvents(forBackgroundURLSession session: URLSession) {
print("后台任务下载完成后回来")
DispatchQueue.main.async {
guard let appDelegate = UIApplication.shared.delegate as? AppDelegate, let backgroundHandler = appDelegate.backgroundSessionCompletionHandler else { return }
backgroundHandler()
}
}
