Swift - 后台获取数据（Background Fetch）的实现

    

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    
    var window: UIWindow?
    
    func application(application: UIApplication,
        didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
            //开启通知
            let settings = UIUserNotificationSettings(forTypes: [.Alert, .Badge, .Sound],
                categories: nil)
            application.registerUserNotificationSettings(settings)
            return true
    }
    
    func applicationWillResignActive(application: UIApplication) {
    }
    
    func applicationDidEnterBackground(application: UIApplication) {
        //虽然定义了后台获取的最短时间，但iOS会自行以它认定的最佳时间来唤醒程序，这个我们无法控制
        //UIApplicationBackgroundFetchIntervalMinimum 尽可能频繁的调用我们的Fetch方法
        application.setMinimumBackgroundFetchInterval(UIApplicationBackgroundFetchIntervalMinimum)
    }
    
    func applicationWillEnterForeground(application: UIApplication) {
    }
    
    func applicationDidBecomeActive(application: UIApplication) {
    }
    
    func applicationWillTerminate(application: UIApplication) {
    }
    
    //后台获取数据
    func application(application: UIApplication,
        performFetchWithCompletionHandler completionHandler: (UIBackgroundFetchResult) -> Void) {
            //创建NSURL对象
            let url:NSURL! = NSURL(string:"http://api.k780.com:88/?app=life.time&appkey=10003&sign=b59bc3ef6191eb9f747dd4e83c99f2a4&format=json")
            //创建请求对象
            let request:NSURLRequest = NSURLRequest(URL: url)
            
            let session = NSURLSession.sharedSession()
            
            let dataTask = session.dataTaskWithRequest(request,
                completionHandler: {(data, response, error) -> Void in
                    if error != nil{
                        print(error?.code)
                        print(error?.description)
                        
                        //让OS知道获取数据失败
                        completionHandler(UIBackgroundFetchResult.Failed)
                    }else{
                        let str = NSString(data: data!, encoding: NSUTF8StringEncoding)
                        print(str)
                        //清除所有本地推送
                        //UIApplication.sharedApplication().cancelAllLocalNotifications()
                        //创建UILocalNotification来进行本地消息通知
                        let localNotification = UILocalNotification()
                        //推送时间（立刻推送）
                        localNotification.fireDate = NSDate(timeIntervalSinceNow: 0)
                        //时区
                        localNotification.timeZone = NSTimeZone.defaultTimeZone()
                        //推送内容
                        localNotification.alertBody = "获取时间成功：\(str)"
                        //声音
                        localNotification.soundName = UILocalNotificationDefaultSoundName
                        UIApplication.sharedApplication().scheduleLocalNotification(localNotification)
                        
                        //让OS知道已经获取到新数据
                        completionHandler(UIBackgroundFetchResult.NewData)
                        //completionHandler(UIBackgroundFetchResult.NoData)
                    }
            }) as NSURLSessionTask
            
            //使用resume方法启动任务
            dataTask.resume()
    }
}