``` val newFragment: Fragment? = if (fragm...

# codereview

[oday]

val newFragment: Fragment? = if (fragment is CarSearchFragment? && fragment == null) {
            CarSearchFragment()
        } else if (fragment is CarValuationFragment? && fragment == null) {
            CarValuationFragment()
        } else if (fragment is HotDealsFragment? && fragment == null) {
            HotDealsFragment()
        } else if (fragment is FavoritesFragment? && fragment == null) {
            FavoritesFragment()
        } else {
            fragment
        }

[louiscad]

This code doesn't work. You can't really do is check on null. Doesn't the IDE warns you about this?

[oday]

ahh that’s right, is is for type not value

[oday]

yea no I dont get a warning

[oday]

what Im looking for is how to do && in when I guess

[dalexander]

val newFragment = if(fragment != null) {
  when() {
    ...
  }
} else {
  fragment
}

or

val newFragment = fragment ?: when(fragment) {
  ...
}

Maybe one of these?

[oday]

hmm yea

[dalexander]

There’s probably another way to improve it because it looks like you are just creating an instance of a particular class when it’s null. ie. you could probably add a function on the companion object that would create an instance of the class if it’s null, so it could be written like
val newFragment = fragment.initIfNull() or something, and that lets you avoid doing all the type checking which generally is good to avoid for OO-design.

[oday]

let me try that yea

[Shawn]

this seems like a broader design problem or at least an a XY issue - you can’t really do cascading type checks on null and this much type checking is no bueno in general unless you’re working with enum or sealed classes with minimal state

[Andreas Sinz]

the following could doesn't work:

val newFragment = fragment?.let { when(it) {
    is CarSearchFragment? -> CarSearchFragment()
    is CarValuationFragment? -> CarValuationFragment()
   ...
}

[Shawn]

I’m pretty sure null will always hit the first branch of the when regardless of what type it might’ve had at the call site

[Andreas Sinz]

nevermind, you are right. Its always the first branch

[oday]

Exactly what was happening to me