"Swift" blockoperation and GCD utility code blocks

blockoperation////viewcontroller.swift Import uikitclass viewcontroller:uiviewcontroller {@IBOutlet weak var imag    e1:uiimageview!    @IBOutlet weak var image2:uiimageview!    @IBOutlet weak var image3:uiimageview!        @IBOutlet weak var image4:uiimageview!        Let imageurls = ["Https://dn-boxueio.qbox.me/image1-big.jpg", "https://dn-boxueio.qbox.me/image2-big.jpg", "Https://dn-boxueio.qbox.me/image3-big.jpg", "https://dn-boxueio.qbox.me/image4-big.jpg"] Overrid e func viewdidload () {super.viewdidload ()//Present (< #T # #viewControllerToPresent: uiviewcontroller# #UIVi  Ewcontroller#&gt, Animated: < #T # #Bool #>, completion:nil)//Do any additional setup after loading the view,    Typically from a nib. } override func Didreceivememorywarning () {super.didreceivememorywarning ()//Dispose of any resources t    Hat can be recreated.         } @IBAction Func Cleardownload (_ Sender:uibutton) {     Self.image1.image=uiimage (named: < #T # #String #>) Self.image1.image = nil self.image2.i Mage = Nil Self.image3.image = Nil Self.image4.image = Nil URLCache.shared.removeAllCachedRes Ponses ()} Let queue = Operationqueue () @IBAction func canceldownload (_ Sender:anyobject) {Self.queu E.cancelalloperations ()} @IBAction func Downloadimages (_ Sender:uibutton) {//Queue.addo            Peration ({/////Let IMG1 = Downloader.downloadimagewithurl (Self.imageurls[0])// OperationQueue.main.addOperation ({//self.image1.image = img1//Self.imag            E1.clipstobounds = true//})///Let OP1 = blockoperation (block: {                Let IMG1 = Downloader.downloadimagewithurl (Self.imageurls[0]) OperationQueue.main.addOperation ({ Self.imagE1.image = Img1 Self.image1.clipsToBounds = true})}) Op1.completionblock = {pri NT ("Image1 downloaded")} Let Op2 = Blockoperation (block: {Let Img2 = Downloader.downloadimagew Ithurl (Self.imageurls[1]) OperationQueue.main.addOperation ({self.image2.image = img 2 Self.image2.clipsToBounds = true}) Op2.completionblock = {print ("Image2 Dow Nloaded ")} Let Op3 = Blockoperation (block: {Let IMG3 = Downloader.downloadimag Ewithurl (self.imageurls[2]) OperationQueue.main.addOperation ({self.image3.image = i MG3 self.image3.clipsToBounds = True})}) Op3.completionblock = {print ("Image3 D Ownloaded ")} Let Op4 = Blockoperation (block: {Let IMG4 = Downloader.downloadim Agewithurl (Self.imageurlS[3]) OperationQueue.main.addOperation ({self.image4.image = Img4 sel           F.image4.clipstobounds = True})}) Op4.completionblock = {print ("Image4 downloaded")} Op3.adddependency (OP4)//Op2.adddependency (OP3) queue.addoperation (OP1) Queue.addop Eration (OP4) queue.addoperation (OP3) queue.addoperation (OP2)}}//GCD Utility code block import Uikitclass Viewcontroller    : Uiviewcontroller {@IBOutlet weak var image1:uiimageview!    @IBOutlet weak var image2:uiimageview!    @IBOutlet weak var image3:uiimageview!        @IBOutlet weak var image4:uiimageview!        Let imageurls = ["Https://dn-boxueio.qbox.me/image1-big.jpg", "https://dn-boxueio.qbox.me/image2-big.jpg", "Https://dn-boxueio.qbox.me/image3-big.jpg", "https://dn-boxueio.qbox.me/image4-big.jpg"] Overrid e func viewdidload () {super.viewdidload ()//Do any ADditional Setup after loading the view, typically from a nib. } override func Didreceivememorywarning () {super.didreceivememorywarning ()//Dispose of any resources t    Hat can be recreated.        } @IBAction Func Cleardownload (_ Sender:uibutton) {Self.image1.image = nil Self.image2.image = Nil     Self.image3.image = Nil Self.image4.image = nil URLCache.shared.removeAllCachedResponses ()} Func Loadimagewithurl (_ url:string), uiimage! {Let data = try?        Data (Contentsof:url (string:url)!)                 Return UIImage (data:data!) } @IBAction Func Downloadimages (_ Sender:uibutton) {var currqueue = Dispatchqueue.global (QoS :. Default)//Currqueue = dispatchqueue (Label: "Com.boxueio.images", Attributes:. Concurrent)//parallel CU        Rrqueue=dispatchqueue (Label: "Currqueue1", QoS:. Default, Attributes:. Concurrent)//Dispatch_async Currqueue.aSync (execute: {Let img1 = Self.loadimagewithurl (Self.imageurls[0]) DispatchQueue.main.async (execute                : {self.image1.image = Img1 Self.image1.clipsToBounds = true})}) Currqueue.async (execute: {Let Img2 = Self.loadimagewithurl (self.imageurls[1]) Dispatchqueu            E.main.async (execute: {self.image2.image = Img2 Self.image2.clipsToBounds = True })}) Currqueue.async (execute: {Let IMG3 = Downloader.downloadimagewithurl (self.imageur LS[2]) DispatchQueue.main.async (execute: {self.image3.image = Img3 self.image3.c Lipstobounds = True})}) Currqueue.async (execute: {Let IMG4 = Downloader.dow Nloadimagewithurl (Self.imageurls[3]) DispatchQueue.main.async (execute: {self.image4.image = img 4 self.imAge4.clipstobounds = True})})}}//class picture base class Import Uikitclass Downloader {class Func Downloa Dimagewithurl (_ url:string), uiimage! {Let data = try?        Data (Contentsof:url (string:url)!)    Return UIImage (data:data!) }}

"Swift" blockoperation and GCD utility code blocks