Synchronous asynchronous download using Nsurlconnection in Swift (instance resolution)

Original blog, reproduced please indicate the source

Http://blog.csdn.net/hello_hwc

One, synchronous asynchronous two concepts

Simply put, synchronization is the function or closure (block in Objective C) that is performed before it can be returned. The asynchronous is returned immediately, and then the callback is performed after the asynchronous execution of the action ends.

second, synchronous download
Sync Download:

class func sendSynchronousRequest(_ request: NSURLRequest,
returningResponse response:AutoreleasingUnsafeMutablePointer<NSURLresponse>
error error:NSErrorPointer)->NSdata?

Parameters:
Request The URLRequest to request
Reponse Callback parameter, the URL returned by the server response
Error Callback parameter to determine if there is an error generating
Here is an example of a picture below
It can be found that when the view appears, the photo already exists, but the view load is slow because it waits for the synchronization download to complete
The complete code:

class ViewController: UIViewController{
    var imageview = UIImageView(frame: CGRectMake(40,40,200,200))
    override func viewDidLoad(){
        super.viewDidLoad()
        imageview.contentMode = UIViewContentMode.ScaleAspectFit
        self.view.addSubview(imageview)
        let url = "http://f.hiphotos.baidu.com/image/pic/item/e1fe9925bc315c60191d32308fb1cb1348547760.jpg"
        let imageURL = NSURL(string:url)
        let urlRequest = NSURLRequest(URL: imageURL!)
        var response:NSURLResponse?
        var error:NSError?
        var data = NSURLConnection.sendSynchronousRequest(urlRequest,returningResponse:&response,error:&error) as NSData?
        if error == nil && data?.length > 0{
            var image:UIImage = UIImage(data:data!)!
            imageview.image = image
        }
    }
    override func didReceiveMemoryWarning(){
        super.didReceiveMemoryWarning()
    }
}

third, asynchronous download

class func sendAsynchronousRequest(_ request: NSURLRequest,
		queue:NSOperationQueue!
		completionHandler handler:(NSURLResponse!,NSData!,NSError!))->Void

Parameters:
Request The URLRequest to request
Queue When a request is completed or an error occurs, the closure is executed on this queue and the UI is changed to execute on the main thread.
Handler When a request is completed or an error occurs, the execution of the closure
Several parameters of closures
Reponse Callback parameter, the URL returned by the server response
Error Callback parameter to determine if there is an error generating
NSData Data downloaded to
Also take a picture as an example
you can see that the view is loaded immediately, but the picture does not appear immediately, and the UI is updated when the picture is downloaded. As you can see, an asynchronous download does not block the UI, causing a bad user experience.
The complete code

class ViewController: UIViewController{
    var imageview = UIImageView(frame: CGRectMake(40,40,200,200))
    override func viewDidLoad(){
    super.viewDidLoad()
    imageview.contentMode = UIViewContentMode.ScaleAspectFit
    self.view.addSubview(imageview)
    let url = "http://f.hiphotos.baidu.com/image/pic/item/e1fe9925bc315c60191d32308fb1cb1348547760.jpg"
    let imageURL = NSURL(string:url)
    let urlRequest = NSURLRequest(URL: imageURL!)
    NSURLConnection.sendAsynchronousRequest(urlRequest,queue:NSOperationQueue.mainQueue(),completionHandler:{
        (response: NSURLResponse!,data:NSData!,error:NSError!)-> Void in
        if error == nil && data?.length > 0{
            var image:UIImage = UIImage(data:data!)!
            self.imageview.image = image
       }
     })
    }
    override func didReceiveMemoryWarning(){
        super.didReceiveMemoryWarning()
    }
}

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Synchronous asynchronous download using Nsurlconnection in Swift (instance resolution)