iOS Swift 多線程阻塞情況

Question

我正在嘗試構建一個應用程序，該應用程序使用大中央調度在后台下載某些圖像。 但是，即使我使用全局隊列來獲取不同的線程並下載圖像，它也會阻塞主線程。 我的代碼由兩個 swift 類組成，一個是 DownloadRequestViewController，另一個是 DownloadHandler。 他們來了：

class DownloadHandler: NSObject {

    let userDefaults = NSUserDefaults.standardUserDefaults()
    var filePath : String = "Turk Isi Manga"

    override init() {
        super.init()
        NSNotificationCenter.defaultCenter().addObserver(self , selector: "downloadChapter:", name: "downloadListNotification", object: DisplayMangaViewController.self)
        NSNotificationCenter.defaultCenter().addObserver(self, selector: "downloadChapter:", name: "downloadListNotification", object: DownloadRequestListViewController.self)
    }

    func downloadChapter(notification : NSNotification){
        dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {
             //Downloading image and save it to memory here
         })
    }

這是我在 DownloadRequestViewController swift 類中調用這個類和 downloadChapter 的方式：

@IBAction func downloadBarButton(sender: AnyObject) {
        dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {
            var obtainedMangaNameArray = [self.obtainedMangaName]
            let userInfo = ["downloadList" : self.selectedChapters , "mangaName" : obtainedMangaNameArray]
            var sdfs = DownloadHandler()
            let notification = NSNotification(name: "downloadListNotification", object: DownloadRequestListViewController.self, userInfo: userInfo)
            sdfs.downloadChapter(notification)
            //NSNotificationCenter.defaultCenter().postNotification(notification)
        })
    }

我究竟做錯了什么？ 任何幫助將不勝感激，謝謝...我在下載章節方法中做什么重要嗎？

Answer 1

請更改此行

dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), {

到這一行

dispatch_async(dispatch_get_global_queue( DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), {

這將在具有后台優先級的線程上執行調度閉包內的代碼，這不會“凍結”主/UI 線程

更新

//Downloader Class

    class DownloadHandler: NSObject {
        class func downloadImageFromURL (url: NSURL) {
            dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), { () -> Void in
                if let imageData: NSData = NSData(contentsOfURL: url) {
                    imageData.writeToFile("Your local Path", atomically: false)
                }
            })
        }
    }

    //Usage example
    DownloadHandler.downloadImageFromURL(NSURL(string: "Your URL To Image")!)

Answer 2

我認為這有效：

func downloadChapter(notification : NSNotification){
        //fetch on different thread
        let qos = Int(QOS_CLASS_USER_INITIATED.value)
        dispatch_async(dispatch_get_global_queue(qos, 0), {
            //download here

            //back to main thread
            dispatch_async(dispatch_get_main_queue(), {
                //if there is something more you wanna do or you can just go back
            })
        })
}

@IBAction func downloadBarButton(sender: AnyObject) {
        var obtainedMangaNameArray = [self.obtainedMangaName]
        let userInfo = ["downloadList" : self.selectedChapters , "mangaName" : obtainedMangaNameArray]
        var sdfs = DownloadHandler()
        let notification = NSNotification(name: "downloadListNotification", object: DownloadRequestListViewController.self, userInfo: userInfo)
        sdfs.downloadChapter(notification)
        //NSNotificationCenter.defaultCenter().postNotification(notification)
}