isInitialized - Backing field of lateinit var is not accessible at this point

55
votes

I'm trying to check if a lateinit property has been initialized.
In Kotlin 1.2 we now have the isInitialized method for that. It works when I do that in the class where the lateinit property is declared. But when I try to call this from another class I get the following warning:

Backing field of 'lateinit var foo: Bar' is not accessible at this point

My model class (let's say Person) is written in Java
Two other classes (let's say Test1 and Test2) are written in Kotlin

Example:

class Test1 {
    lateinit var person: Person

    fun method() {
        if (::person.isInitialized) {
            // This works
        }
    }
}

-

class Test2 {
    lateinit var test1: Test1

    fun method() {
        if (test1::person.isInitialized) {
            // Error
        }
    }
}

Any chance to get this working?

My current workaround is to make a method in Test1 which returns isInitialized from the person property. 

fun isPersonInitialized(): Boolean = ::person.isInitialized

//in Test2:
if (test1.isPersonInitialized()) {
    // Works
}
3
javakotlinkotlin-lateinit
I don't know the answer. But why you use isInitialized over nullable? lateinit show always be initialized before the object being use. – Joshua
@Eledgy your code does not compile. you cannot put an if-expression directly in a class body. i think you forgot to wrap it inside an init block. i know, this does not fix your inital problem. – Willi Mentzel
@Joshua I have one case where person may not be initialized yet – ElegyD
@WilliMentzel It's just an example, I've put the code in a method – ElegyD
@ElegyD Then, you should use Person?. If you abuse lateinit, you need an if everytime you access person which make you go back to Java with null checking. – Joshua

3 Answers

26
votes

According to the docs:

This check is only available for the properties that are lexically accessible, i.e. declared in the same type or in one of the outer types, or at top level in the same file.

Which is why you cannot check that in the main function.

71
votes

A really simple workaround to the constraints described by the accepted answer is the following:

class LateClass {
    lateinit var thing: Thing
    fun isThingInitialized() = ::thing.isInitialized
}

class Client {
    val lateClass = LateClass()
    ... things happen ...
    if (lateClass.isThingInitialized() {
        // do stuff with lateClass.thing, safely
    }
}
8
votes

My version as a Kotlin property.

class LateClass {
    lateinit var thing: Thing
    val isThingInitialized get() = this::thing.isInitialized 
}