Swift: unrecognized selector sent to instance, how to detect null value? - ios

Question

I am trying to use Microsoft Graph iOS SDK and followed the official code sample.
The following code snippet is to get basic profile of all users in the organization:
private func getContactInfo(){
self.graphClient.users().request().getWithCompletion{
(collection: MSCollection?, request:MSGraphUsersCollectionRequest?, error: NSError?) in
if let users = collection {
for user: MSGraphUser in users.value as! [MSGraphUser] {
print(user)
print(String(user.surname.dynamicType))
print(user.mobilePhone)
}
}
}
}
Output Result:
{
businessPhones = (
);
displayName = "Boss";
givenName = "Jack";
id = "30fb78ff-522f-45e7-a9cd-75ba8ee2eca6";
jobTitle = "<null>";
mail = "boss#abc.net";
mobilePhone = "<null>";
officeLocation = "<null>";
preferredLanguage = "<null>";
surname = "\U8a79";
userPrincipalName = "boss#abc.net";
}
ImplicitlyUnwrappedOptional<String>
And runtime exception happened
2016-06-05 17:02:55.302 ABC[76976:915052] -[NSNull _fastCStringContents:]: unrecognized selector sent to instance 0xb59398
2016-06-05 17:02:55.305 ABC[76976:915052] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSNull _fastCStringContents:]: unrecognized selector sent to instance 0xb59398'
*** First throw call stack:
(
0 CoreFoundation 0x0092c494 __exceptionPreprocess + 180
1 libobjc.A.dylib 0x02640e02 objc_exception_throw + 50
...
When I try to print the null value like mobilePhone, runtime exception occurred. How to detect null value to avoid crashing? Thank you.
Add: MSGraphUser.m snippet used in this case,
#interface MSGraphUser()
{
...
NSString* _mobilePhone;
...
- (NSString*) mobilePhone
{
return self.dictionary[#"mobilePhone"];
}
...

Answer 1

There must be a better swift support, but for now, you could extend the class like what Casey has said.
If you did this, you can check
if user.optMobilePhone is NSNull
The actual extension would look something like this:
extension MSGraphUser {
var optMobilePhone: AnyObject? {
return dictionaryFromItem()["mobilePhone"]
}
}

Answer 2

You can use one way to filter null objects
- (NSString* __nullable) mobilePhone
{
if ([self.dictionary isKindOfClass:[NSString class]])
{
return self.dictionary[#"mobilePhone"];
}
return nil;
}
or
- (NSString* __nullable) mobilePhone
{
if (![self.dictionary isKindOfClass:[NSNull class]]) {
return self.dictionary[#"mobilePhone"];
}
return nil;
}

Answer 3

Many JSON APIs will return null in the JSON document for values that they want to mark explicitely as not present. This is different from keys that will not be reported at all.
The first thing you do is check with the creator of the API or with the documentation how that kind of value should be interpreted. For example, if you ask for the key "user", you might find that the value isn't present at all, that the value is null, or that the value is an empty string. Find out how each value should be interpreted, or if they should be treated the same.
Then since you will need this all the time, you add a function to NSDictionary that will return what you want, and logs things that you didn't expect. You check that a value isn't there at all by checking with if let ... . You check whether a value is null by checking value == NSNull (). And then you make that function return either an optional string or a string.

Answer 4

It looks like mobilePhone can actually return a NSString or NSNull so it should be declared as - (id) mobilePhone. Since it's not, we can extend MSGraphUser
extension MSGraphUser {
var optMobilePhone : String? { return self.dictionary["mobilePhone"] as? String }
}
And then use that computed property to safely access the value:
for obj in users.value {
if let user = obj as? MSGraphUser {
print(user)
print(String(user.surname.dynamicType))
print(user.optMobilePhone ?? "no phone")
}
}