CoreNFC: Lock in application switch

Question

Created Jul ’17

Replies 1

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Participants 2

When my CoreNFC application reads a tag that contains a valid URL, it attempts to open this URL.

This works for a while, but suddenly the switch no longer completes: The other application (e.g. Safari) starts to open and then hangs on a black screen. Just to debug things, I am launching my own test application and can see that applicationDidBecomeActive is called, but that's the end of it.

I created another test application that does the exact same thing as my NFC application, except that the app switch is initiated by clicking a button instead of scanning a tag. This application works fine. So I think the issue is somehow tied to NFC itself, possibly a bug.

If anyone wants to reproduce this, start by downloading the sample app here: https://developer.apple.com/sample-code/wwdc/2017/CoreNFC-Tag-Reading.zip

Once you verify that the app is running, add this code to the MessagesTableViewController right after "detectedMessages.append(contentsOf: messages)":

let message = messages[0]
let record = message.records[0]
if let type = String(data: record.type, encoding:.utf8) {
     if type == "U" {
          if let payloadText = String(data: record.payload, encoding:.utf8) {
               var url = payloadText
               let prefix = url.remove(at: url.startIndex)
               if prefix == "\u{0}" {
                   if let realURL = URL(string: url) {
                        DispatchQueue.main.async {
                        UIApplication.shared.open(realURL, options: [:], completionHandler: nil)
                   }
               }
           }
       }
   }
}

In my case, I am scanning a variety of tags containing one single "Well Known" NDEF Record of Type "URL" each. Some examples:

fb://feed (launches Facebook)
tel:+415555555 (calls number)
twitter://timeline (opens Twitter)
http://www.apple.com (Opens Safari)

Sooner or later, after scanning tags for a while, the problen starts to appear.

Does anyone else see this problem? Am I making a mistake, or should I report this as a possible bug?

Thanks! Martin

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Answer 1

latorreSTM OP

Sep ’17

Hi Martin,

I saw the same issue since iOS11Beta3....I didn't know why, but I suspected NFC scanning thread while opening URL.

My workaround was to stop NFCScan, then to add a short delay in didDetectNDEF callback before calling openURL. As I thought it came from my code, I didn't post a possible bug....but now, I have a doubt :-)

Here after, my workaround :

func readerSession(_ session: NFCNDEFReaderSession, didDetectNDEFs messages: [NFCNDEFMessage])

{

stopNFCReaderSession()

.......blablabla

DispatchQueue.main.asyncAfter(deadline: .now() + 2.0) {

UIApplication.shared.open(...)

}

Hope it helps.

BR,

Vincent

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