when I try and create a SparseArray, like this: `...

# android

[Andrew Ebling]

when I try and create a SparseArray, like this:

var array = SparseArray<ByteArray>(1)

...array ends up being empty (it shows as “null” in the debugger, and if I do this:


array.setValueAt(0, byteArrayOf(byte)
val value = array.get(0)

...then value is null.

[mkrussel]

The 1 in that constructor is the initial capacity, the SparseArray is still empty. You can just add 1 item to the array without it needing to allocate more memory

You need to fill it like you would a map.

[Andrew Ebling]

sorry - I realised my question was incomplete - I just updated it. I try to set the first value, but the subsequent get() still returns null

[Andrew Ebling]

also array.size() returns zero, even after the setValue()

[mkrussel]

So the size is 0 still since the array is empty. From documentation for setValue

For indices outside of the range 0...size()-1, the behavior is undefined for apps targeting Build.VERSION_CODES.P and earlier, and an ArrayIndexOutOfBoundsException is thrown for apps targeting Build.VERSION_CODES.Q and later.

I'm guessing you want to use the put method.

[Andrew Ebling]

thanks - seeing the same with put unfortunately

[mkrussel]

I've not used the class, but switching from setValueAt to put should do what you want from reading the documentation

[Andrew Ebling]

is there a way I can create the SparseArray with it’s contents already in place?

[Andrew Ebling]

I’ve not used this class before but I’m trying to create some mock data for a unit test

[Andrew Ebling]

and the API I’m mocking returns SpareArray s unfortunately

[mkrussel]

Are you running this on device/emulator or as a simple JVM test?

Is the code in fold test or androidTest. If running in test then that is because a fake version of SparseArray is being used and default values are returned for everything. You will have to mock the SparseArray also.

[Andrew Ebling]

ah - this would explain a lot!

[Andrew Ebling]

I just tried it in a Scratch and got this instead:

Exception in thread “main” java.lang.RuntimeException: Stub!
at android.util.SparseArray<init>(SparseArray.java:25)

[Andrew Ebling]

thanks very much for your help @mkrussel ! 👍

[gildor]

Do not use platform version of SparseArray, use Androidx one instead, to avoid all those version specific differences and at least make it testable https://developer.android.com/reference/androidx/collection/SparseArrayCompat

[gildor]

But also I would just do not use SparseArray at all, until you have some very good reason except general recommendation