Convert an ArrayMap to ArrayList - Kotlin

Question

I have an ArrayMap and I want a list of Chat to create and recyclerview.

val chats : ArrayMap<String,Chat>? = ArrayMap()

RecyclerView.Adapter

class ChatAdapter(var chats : ArrayList<Chat>){
   .
   .
   .
}

I get this ArrayMap from firebase. What is the best way to get an ArrayList?

guenhter · Accepted Answer · 2017-07-03 05:53:22Z

2

You shouldn't use ArrayList in the public constructor (because then you make youself depending on exactly that implementation). Should be the MutableList interface:

class ChatAdapter(var chats : MutableList<Chat>){

I guess the ArrayMap is a usual Map (because I don't know that class). You can just write

val chats : ArrayMap<String,Chat>? = ArrayMap()
// ... initialize the chat
val adapter = ChatAdapter(am.values.toMutableList())

If you really need the ArrayList class for some reason, you can write

val adapter = ChatAdapter(ArrayList(am.values))

edited Jul 3, 2017 at 5:53

answered Jul 3, 2017 at 5:31

guenhter

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7 Comments

Beto Caldas Over a year ago

I can't understande this "You shouldn't use ArrayList in the public constructor (because then you make youself depending on exactly that implementation).", but your second solution works: val adapter = ChatAdapter(ArrayList(am.values))

Beto Caldas Over a year ago

I found this other solution: ChatAdapter(user.chats.map { it.value } as ArrayList<Chat>)

guenhter Over a year ago

ArrayList is an implementation, MutableList an interface. If possible, always use the interface e.g. in your case use the interface in the constructor. Because then you can pass ANY implementation (as ArrayList) to your ChatAdapter. Else you can just pass an ArrayList.

guenhter Over a year ago

I wouldn't use user.chats.map { it.value } as ArrayList<Chat> because this has much more runtime overhead than ArrayList(am.values)

guenhter Over a year ago

Yes, this describes it quite well.

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dedda1994 · Accepted Answer · 2017-07-06 13:10:05Z

0

If you don't need an ArrayList explicitly, you can use the ArrayMap.map() function like this:

val chats : ArrayMap<String,Chat>? = ArrayMap()
val list : List<Chat> = chats.map { it.value }

answered Jul 6, 2017 at 13:10

dedda1994

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2 Comments

Beto Caldas Over a year ago

I commented about this on checked solution.

dedda1994 Over a year ago

Thanks. I already thought it might be more expensive at runtime but wasn't sure so i thought it might not hurt to see another possible way. At least it's not completely wrong i guess.

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