Core Data iOS11 - NSUnknownKeyException crash in sectionNameKeyPath with custom property [duplicate]

Question

I have a Swift library which is heavily reliant on obj.valueForKey() from NSObject.

After migrating to Swift 4 I've found that these calls always crash with the error "this class is not key value coding-compliant for the key..." unless the property I'm looking for is declared with @objc.

Is it now mandatory to declare properties with @objc for them to be found with this method? Is there an alternative?

Answer 1

When you performed the migration Xcode asked about @objc inference and you probably selected the new type instead of Swift3.

Possible solutions:

Use @objc

Use @objc on each method, as needed instead of the whole class.

Use @objcMembers

You could just use @objcMembers on the class.

Applying @objcMembers attribute to a class implicitly adds the @objc attribute to all of its Objective-C compatible members.

Writing Swift Classes and Protocols with Objective-C Behavior

Keep in mind: because applying the @objc attribute can increase the compiled size of an app and adversely affect performance, only apply the @objcMembers attribute on declarations when each member needs to have the @objc attribute applied.

Switch inference to the old behavior

You can also change the project's behavior under: Build Settings > Swift 3 @objc Inference > On/Off

Related questions:

• The use of Swift 3 @objc inference in Swift 4 mode is deprecated?
• How can I deal with @objc inference deprecation with #selector() in Swift 4?