How to Cancel download in Queue using Swift - ios

Question

I have an app where user can download multiple files, sequentially. I have followed Mr. Rob's solution for the sequential downloads. However, I have problem when I try to cancel the download.
There are two situation when I try to cancel the download.
I want to cancel the current downloading file. When I cancel that file, the download can proceed to the next file in the queue
I want to cancel the file that are currently in the queue. The queue has cancelAll() method which will cancel all file in the queue.
Here is the codes
DownloadManager.swift
class DownloadManager: NSObject, NSURLSessionTaskDelegate, NSURLSessionDownloadDelegate
{
/// Dictionary of operations, keyed by the `taskIdentifier` of the `NSURLSessionTask`
internal var delegate : DownloadVC!
private var operations = [Int: DownloadOperation]()
/// Serial NSOperationQueue for downloads
let queue: NSOperationQueue = {
let _queue = NSOperationQueue()
_queue.name = "download"
_queue.maxConcurrentOperationCount = 1
return _queue
}()
/// Delegate-based NSURLSession for DownloadManager
lazy var session: NSURLSession = {
let sessionConfiguration = NSURLSessionConfiguration.defaultSessionConfiguration()
return NSURLSession(configuration: sessionConfiguration, delegate: self, delegateQueue: nil)
}()
/// Add download
///
/// - parameter URL: The URL of the file to be downloaded
///
/// - returns: The DownloadOperation of the operation that was queued
func addDownload(URL: NSURL) -> DownloadOperation
{
print("url in download manager: \(URL)")
let operation = DownloadOperation(session: session, URL: URL)
operations[operation.task.taskIdentifier] = operation
queue.addOperation(operation)
return operation
}
/// Cancel all queued operations
func cancelAll()
{
queue.cancelAllOperations()
}
// func cancelOne()
// {
// operations[identifier]?.cancel()
// print("identifier : \(identifier)")
// //queue.operations[identifier].cancel()
// // cancelAll()
// }
// MARK: NSURLSessionDownloadDelegate methods
func URLSession(session: NSURLSession,
downloadTask: NSURLSessionDownloadTask,
didFinishDownloadingToURL location: NSURL)
{
print("downloadTask.taskIdentifier \(downloadTask.taskIdentifier)")
operations[downloadTask.taskIdentifier]?.delegate = delegate
operations[downloadTask.taskIdentifier]?.URLSession(session, downloadTask: downloadTask, didFinishDownloadingToURL: location)
}
func URLSession(session: NSURLSession,
downloadTask: NSURLSessionDownloadTask,
didWriteData bytesWritten: Int64,
totalBytesWritten: Int64,
totalBytesExpectedToWrite: Int64)
{
operations[downloadTask.taskIdentifier]?.delegate = delegate
operations[downloadTask.taskIdentifier]?.URLSession(session, downloadTask: downloadTask, didWriteData: bytesWritten, totalBytesWritten: totalBytesWritten, totalBytesExpectedToWrite: totalBytesExpectedToWrite)
}
// MARK: NSURLSessionTaskDelegate methods
func URLSession(session: NSURLSession,
task: NSURLSessionTask,
didCompleteWithError error: NSError?)
{
let key = task.taskIdentifier
operations[key]?.URLSession(session, task: task, didCompleteWithError: error)
operations.removeValueForKey(key)
}
}
DownloadOperation.swift
class DownloadOperation : AsynchronousOperation
{
let task: NSURLSessionTask
var percentageWritten:Float = 0.0
var delegate : DataDelegate!
init(session: NSURLSession, URL: NSURL)
{
task = session.downloadTaskWithURL(URL)
super.init()
}
override func cancel() {
task.cancel()
super.cancel()
}
override func main() {
task.resume()
}
// MARK: NSURLSessionDownloadDelegate methods
func URLSession(session: NSURLSession,
downloadTask: NSURLSessionDownloadTask,
didWriteData bytesWritten: Int64,
totalBytesWritten write: Int64,
totalBytesExpectedToWrite expect: Int64)
{
//download bar progress
percentageWritten = Float(write) / Float(expect)
//progressBar.progress = percentageWritten
let pW = Int(percentageWritten*100)
delegate.didWriteData(pW)
}
// using cocoa Security for encryption and decryption
func URLSession(session: NSURLSession,
downloadTask: NSURLSessionDownloadTask,
didFinishDownloadingToURL location: NSURL)
{
let documentsDirectoryURL = NSFileManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).first as NSURL?
print("Finished downloading!")
print(documentsDirectoryURL)
let downloadLocation = "\(location)".stringByReplacingOccurrencesOfString("file://", withString: "")
let fileData = NSFileManager().contentsAtPath(downloadLocation)
delegate.didFinishDownloadingToUrl(fileData!)
}
// MARK: NSURLSessionTaskDelegate methods
func URLSession(session: NSURLSession,
task: NSURLSessionTask,
didCompleteWithError error: NSError?)
{
completeOperation()
if error != nil {
print(error)
}
}
}
AsynchronousOperation.swift
class AsynchronousOperation : NSOperation
{
override var asynchronous: Bool { return true }
private var _executing: Bool = false
override var executing: Bool
{
get
{
return _executing
}
set {
if (_executing != newValue)
{
self.willChangeValueForKey("isExecuting")
_executing = newValue
self.didChangeValueForKey("isExecuting")
}
}
}
private var _finished: Bool = false
override var finished: Bool
{
get
{
return _finished
}
set
{
if (_finished != newValue)
{
self.willChangeValueForKey("isFinished")
_finished = newValue
self.didChangeValueForKey("isFinished")
}
}
}
func completeOperation()
{
if executing {
executing = false
finished = true
}
}
override func start()
{
if (cancelled) {
finished = true
executing = false
return
}
executing = true
main()
}
}
DownloadViewController.swift
This is where I want to cancel the download.
if cell.downloadLabel.currentTitle == "CANCEL"
{
print("cancel button was pressed")
downloadManager.cancelAll()
// I want to put the codes here
let defaults: NSUserDefaults = NSUserDefaults.standardUserDefaults()
let key = cell.stringId
print("key : \(key)")
defaults.setBool(false, forKey: key)
defaults.synchronize()
cell.accessoryType = UITableViewCellAccessoryType.None
cell.downloadLabel.backgroundColor = UIColor.redColor()
cell.downloadLabel.setTitle("DOWNLOAD", forState: .Normal)
}
For situation 1, I have tried to use do
queue.operations[identifier].cancel()
but it crash saying
*** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayI objectAtIndex:]: index 1 beyond bounds [0 .. 0]'
For situation 2, I have tried to put all downloaded urls in an array, add into queue, once the cancel button is clicked, it will cancelAll() queue, remove the cancel one from queue and re-insert the remaining urls back into the array. However, it won't work
Can anybody help me to satisfy both situation?

Answer 1

You need to keep a reference to the NSOperation instance. Then you can call cancel on it.