iosswifterror-handlingruntime-errornsunknownkeyexception

Handle uncaught exception valueForUndefinedKey in Swift

I have a third party library class whose source is not open to me. For example like this:

class MyClass: NSObject {
    let myProperty = 10
}

I can get myProperty value like this.

let test = MyClass().value(forKey: "myProperty")  // 10

I want to check whether myProperty exists in MyClass. Reason is I don't want my app to crash if the 3rd party class implementation changes in future.

For testing I've tried 

guard let test = MyClass().value(forKey: "myProperty1") else { return }  // crash

if let test = MyClass().value(forKey: "myProperty1") { }  // crash

do {
    let test = try MyClass().value(forKey: "myProperty1")  // crash
} catch { }

In every way I get crash.

*** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<__lldb_expr_80.MyClass 0x608000223a00> valueForUndefinedKey:]: this class is not key value coding-compliant for the key myProperty1.'

Solution

  • You must find a better solution by talking to lib dev

    You can use Mirror reflection and check its objects label

    let myClass = Mirror(reflecting: MyClass())
for (_, attr) in myClass.children.enumerated() {
  if let propertyName = attr.label, propertyName == "myProperty"{
   print(propertyName, attr.value)
  }
}