Getting kotlin.TypeCastException when trying to use parcelable on an ArrayList variable which contains null fields

Question

I literally started yesterday with using Kotlin, so I am still having a hard time understanding the underlying principles. I want to send an object via intent to another activity and implemented parcelable on the object. The object contains some MutableLists in the form of:

var favoritePlaces: MutableList<String?>? = null

I used this method constructor to parcelize it:

constructor(`in`: Parcel) {
  `in`.readList(favoritePlaces, String::class.java.classLoader)
}

This is the error I get in Android Studio since a type mismatch exists:

I tried to go with the suggestion of Android Studio leaving me with this here in the constructor:

constructor(`in`: Parcel) {
   `in`.readList(favoritePlaces as List<*>, String::class.java.classLoader)
 }

And in the writeToParcel method:

override fun writeToParcel(dest: Parcel, flags: Int) {
    dest.writeList(favoritePlaces as List<*>?)
}

But when I try to use this, then I get the following error message when starting the Activity:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.test.app.Activity}: kotlin.TypeCastException: null cannot be cast to non-null type kotlin.collections.List<*>

I do understand that the type kotlin.collections.List<*> is a non-null type and since I have some null fields in my arrays, it makes sense that this error occurs. My question is now, how can I parcelize String Arrays in Kotlin with non-empty as well as empty fields???

Alexey Romanov · Accepted Answer · 2020-02-26 07:35:33Z

1

readList expects a non-null argument list to which it will add elements, so you need to initialize it before calling readList:

favoritePlaces = mutableListOf<String?>()
`in`.readList(favoritePlaces as List<*>, String::class.java.classLoader)

Or better,

favoritePlaces = `in`.createStringArrayList()

But in Kotlin there's basically no reason to do this manually; use @Parcelize instead if possible (you'll need to move properties to the primary constructor instead of class body).

edited Feb 26, 2020 at 7:35

answered Feb 26, 2020 at 7:29

Alexey Romanov

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1 Comment

Benny Over a year ago

Thanks for this, I was thinking of using @Parcelize and had a look at it, it seems great to use an autogenerator to parcelize it, saves some boilerplate!

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