Swift: Proper Firebase error-handling -

i'm not able understand why neither print lines executed when running following code:

ref.child("schools/\(schooltextfield.text!)/settings/pin").observesingleevent(of: .value, with: { (snapshot) in     print(snapshot.value) }, withcancel: { (error) in     print(error.localizeddescription) }) 

it used work, until made changes regarding firebase authentication, don't see why withcancel block not executed!

how catch whatever error occuring here? no error-message printed in log.

edit: found similar question here suggests problem might related authentication after all. in appdelegate's didfinishlaunchingwithoptions check if user auth-token exists in firebase auth:

auth.auth().currentuser?.getidtokenforcingrefresh(true, completion: { (response, error) in     guard error == nil, let uid = response else {         print(error)         return     }     ... }) 

in current case there error, printed:

error domain=firautherrordomain code=17011 "there no user record corresponding identifier. user may have been deleted."

i'm getting these errors printed in log:

[common] _bsmacherror: port b43b; (os/kern) invalid capability (0x14) "unable insert copy_send" [common] _bsmacherror: port b43b; (os/kern) invalid name (0xf) "unable deallocate send right"

try way:

if let snapshot = snapshot.children.allobjects as? [datasnapshot] {  snap in snapshots {    print("snap: \(snap)")  } 

also error code 17011 user not found error see firautherrorcode more info it's better create dataservice class handle interaction firebase see creating reusable firebase data service more info.