Swift gist

iOSCodeGist.swift

// multithread

// 1. GCD
DispatchQueue.global(qos: DispatchQoS.QoSClass.default).async {
    var data:Data?
    if let imageURL = URL(string: imageURLStr) {
        data = try? Data(contentsOf: imageURL)
    }
    DispatchQueue.main.async(execute: {
        if data == nil {
            cell.itemImage.setImage(UIImage(named: "NoImageFound.png"), for: UIControlState())
        } else {
            cell.itemImage.setImage(UIImage(data:data!), for: UIControlState())
        }
    })
}

// 2. URLSession.shared.dataTask
// No need to provide background queue when use this. DispatchQueue.main is used since completion block run on background
// explaninations: [SO post](https://stackoverflow.com/questions/31746229/does-nsurlsession-for-http-data-task-nsurlsessiondatatask-runs-in-background-t)
URLSession.shared.dataTask(with: request as URLRequest) { (data, response, error) in
    DispatchQueue.main.async(execute: { 
    })
}.resume()

// 3. NSURLConnection.sendAsynchronousRequest
// Need to provoide a operationQueue when doing this
let queue:OperationQueue = OperationQueue()
NSURLConnection.sendAsynchronousRequest(request as URLRequest, queue: queue, completionHandler:{(response: URLResponse?, data: Data?, error: Error?) -> Void in
    DispatchQueue.main.async(execute: {
                            })
})