Cast Array<String?> to Array<String> in Kotlin?

Question

I have an array of nulls that I initialize with Strings. Then I have to pass it to a function that requires Array<String> instead of Array<String?>. So how can I go around this issue?

val list_names = arrayOfNulls<String>(plant_list.size)
for(item in plant_list){ list_names.plus(item.name) }

val myListAdapter = MyListAdapter(activity!!,list_names,list_types,list_images) // list_names must be Array<String>

I also want to mention that changing it in the Adapter would only complicate things, so I would like to do it all from here.

"Array instead of Array" what it means?

Bruno Martins
– Bruno Martins

2020-01-09 13:06:05 +00:00
Commented Jan 9, 2020 at 13:06 — Bruno Martins
– Bruno Martins, Commented Jan 9, 2020 at 13:06

Roland · Accepted Answer · 2020-01-09 14:02:58Z

2

If you are sure that no null-values will be in your nullable array, you can simply (unsafe) cast it and it will work, e.g.:

val myListAdapter = MyListAdapter(activity!!,list_names as Array<String>,list_types,list_images)

If you have null values in there it depends a bit. One approach is then to first filter out the null-values and pass the resulting array, e.g.:

list_names.filterNotNull().toTypedArray()
// or in case you have different types in there and want only want a single matching one:
list_names.filterIsInstance<String>().toTypedArray()

But if you can: try to omit holding that array of nullable type in the first place. Can't you just filter out null values and collect the non-nullable only? That would probably the easiest and nicest way to collect the names as Array<String>, e.g.:

val list_names = plant_list.mapNotNull { it.name }.toTypedArray()

edited Jan 9, 2020 at 14:02

answered Jan 9, 2020 at 13:33

Roland

23.5k5 gold badges62 silver badges91 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Tenfour04 · Accepted Answer · 2020-01-09 13:41:39Z

2

To answer your direct question you can get a new Array without nulls using this:

val nonNullListNames = list_names.filterNotNull().toTypedArray()

But there are other issues with your code. There's no reason to create the array of nulls and add items to it. Every time you call list_names.plus(item.name) in your loop, you are creating a new Array that still has the original set of null values plus your new item(s).

Instead you can directly create a list of non-null items from the collection you're getting items from, and convert it to an Array:

val nonNullNamesArray = plant_list.map { it.name }.toTypedArray()

If your plant names are nullable, use this:

val nonNullNamesArray = plant_list.mapNotNull { it.name }.toTypedArray()

edited Jan 9, 2020 at 13:41

answered Jan 9, 2020 at 13:36

Tenfour04

95.1k14 gold badges125 silver badges181 bronze badges

Comments

Bruno Martins · Accepted Answer · 2020-01-09 13:09:57Z

1

You cannot have a arrayOfNulls and convert a Nullable to a NonNull object. What I recommend to you is:

val list_names = mutableListOf<String>()
plant_list.foreach {
    list_names.add(it.name)
}
val myListAdapter = MyListAdapter(activity, list_names, list_types, list_images)

answered Jan 9, 2020 at 13:09

Bruno Martins

1,4832 gold badges14 silver badges33 bronze badges

Collectives™ on Stack Overflow

Cast Array<String?> to Array<String> in Kotlin?

3 Answers 3

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related