urlsessiondatadelegate.swift

//MARK: - URLSessionDataDelegate
extension ViewController: URLSessionDataDelegate {

    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive response: URLResponse, completionHandler: @escaping (URLSession.ResponseDisposition) -> Void) {
        
        guard let httpResponse = response as? HTTPURLResponse, (200...299).contains(httpResponse.statusCode) else {
            completionHandler(.cancel)
            return
        }
        
        //get full lenth of your content
        expectedContentLength = Int(response.expectedContentLength)
        
        completionHandler(.allow)
    }
    
    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
        
        self.receivedData?.append(data)
        
        //count percent and update progress
        if let receivedCount = self.receivedData{
            let percentageDownload = Float(receivedCount.count / self.expectedContentLength)
            DispatchQueue.main.async {
                self.progressView1.progress = percentageDownload
            }
        }
        
    }
    
    func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?){
        
        DispatchQueue.main.async {
            self.button1.isEnabled = true
            self.progressView1.progress = 1.0
            
            if let error = error {
                self.handleClientError(error)
            }
            
            //when completed receive data, put data to imageview
            if let receivedData = self.receivedData {
                self.imageview1.image = UIImage(data: receivedData)
            }
            
        }
    }
    
}