FCNDEFMessage queryNDEFStatusWithCompletionHandler:]: unrecognized selector sent to instance - ios

Question

I'm trying to obtain some information about a NFC tag, the session is successfully started and after reading a tag, we jump into the following function:
- (void) readerSession:(NFCNDEFReaderSession *)session didDetectNDEFs:(NSArray<NSObject<NFCNDEFTag> * > *)tags {
NSLog(#"NFCNDEFReaderSession didDetectNDEFs");
for (NSObject<NFCNDEFTag> *tag in tags) {
[tag queryNDEFStatusWithCompletionHandler:^(NFCNDEFStatus status, NSUInteger capacity, NSError * _Nullable error) {
if (!error) {
NSLog(#"success");
}
}];
}
}
We even get an iteration in the loop, but in the moment I try to obtain some information about my tag, the app crashes with the following error message:
019-11-06 16:01:12.955810+0100 MyApp[336:10691] -[NFCNDEFMessage queryNDEFStatusWithCompletionHandler:]: unrecognized selector sent to instance 0x281cfce30
2019-11-06 16:01:12.956200+0100 MyApp[336:10691] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NFCNDEFMessage queryNDEFStatusWithCompletionHandler:]: unrecognized selector sent to instance 0x281cfce30'
*** First throw call stack:
(0x18e45180c 0x18e179fa4 0x18e35536c 0x18e455c88 0x18e457a6c 0x100636cc0 0x100b097fc 0x100b0abd8 0x100b11b48 0x100b12718 0x100b1dadc 0x18e16ef88 0x18e171ad4)
libc++abi.dylib: terminating with uncaught exception of type NSException
Note: NFCNDEFTag is a protocol, so maybe it's connected with the way I'm declaring it: NSObject<NFCNDEFTag>?

Answer 1

Let's see the doc of NFCNDEFReaderSessionDelegate.
You have:
- (void)readerSession:(NFCNDEFReaderSession *)session
didDetectNDEFs:(NSArray<NFCNDEFMessage *> *)messages;
and
- (void)readerSession:(NFCNDEFReaderSession *)session
didDetectTags:(NSArray<__kindof id<NFCNDEFTag>> *)tags;
You wrote:
- (void)readerSession:(NFCNDEFReaderSession *)session
didDetectNDEFs:(NSArray<NSObject<NFCNDEFTag> * > *)tags {
Which is a mix of the two.
But in Objective-C, the selector will be:
readerSession:didDetectNDEFs & readerSession:didDetectTags: for the official one, and yours is readerSession:didDetectNDEFs, which is the same as the first one. So you lured the compiler and the runtime for yours.
But it doesn't care of the type of the parameters, so it's not the correct object, so it doesn't implement the method queryNDEFStatusWithCompletionHandler:, so it crashes with that error message.
How to fix it?
Implement the real delegate methods, with the good parameters types, use the correct one, you can't modify them like that as you want.