iOS 10 Notification Content Extension: using NSURLSession? - ios

Question

I'm trying to create a new Notification Content Extension in iOS 10 for local notifications where the notification view controller responsible for the content extension downloads an image from the network and renders it in a UIImageView. I have the Notification Content Extension target set up with an appropriate Info.plist and the content extension works beautifully for simple things like rendering a label with some content, for example the sample code that comes in the template:
func didReceive(_ notification: UNNotification) {
self.label.text = notification.request.content.body
}
However, when I try to introduce NSURLSession (or URLSession in Swift 3) into the mix, the notification content totally fails to load - not even the label gets set anymore:
func didReceive(_ notification: UNNotification) {
self.label.text = notification.request.content.body
let session = URLSession.shared()
let url = URL(string: "https://chart.googleapis.com/chart?cht=p3&chs=250x100&chd=t:60,40&chl=Hello|World")!
let task = session.downloadTask(with: url) { (fileURL, response, error) in
if let path = fileURL?.path {
DispatchQueue.main.async {
self.imageView.image = UIImage(contentsOfFile:path)
}
}
}
task.resume()
}
Is the usage of NSURLSession in the notification content extension not allowed? Is my extension possibly being killed before the download completes? If so, how could I ensure that it's not killed so I can download and render the image?

Answer 1

At the point when func didReceive(_ notification: UNNotification) is called in the Content extension, any modifications to the content such as downloading images should have already occurred.
It seems that you use a Notification Service Extension to do the downloading of any additional content. The Notification Content extension is only responsible for providing a custom user interface if you need one.
In your Service extension you download the image using the url in the notification payload, and set it as an attachment on the UNNotification object. If you don't need any custom UI, the system will automatically display visual media attachments like a video or an image. If that suits your needs, you don't actually need a Notification Content Extension at all.
Pusher provide a great tutorial on setting up a Notification Service Extension for handling media attachments in push notifications on iOS 10 right here.

Answer 2

It's actually possible to download images in a Notification Content Extension. However, your code contains two problems:
The URL is not valid.
The fileURL returned by the downloadTask methode is deleted as soon as the function runs out of scope, which is already the case when you try to access the fileURLfrom another thread. Instead it's better to catch the fileURL content in a data variable and use that to produce an image in the main thread
Slightly corrected code:
guard let url = URL(string: "https://betamagic.nl/images/coredatalab_hero_01.jpg") else {
return
}
let task = URLSession.shared.downloadTask(with: url) { (fileURL, response, error) in
if let fileURL = fileURL,
let data = try? Data(contentsOf: fileURL) {
DispatchQueue.main.async {
self.imageView.image = UIImage(data: data)
}
}
}
task.resume()

Answer 3

Disable app transport security in Info.plist for you extension.
Tip: move file from tmp folder to cache for save