Hi guys, How can the second sentence produce a Nu...

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[KayCee]

Hi guys,
How can the second sentence produce a NullPointerException?

lateinit var aLiveData: LiveData<List<..>>
val list = aLiveData.value

The crashlytics said there is a NPE in the second line. It occurs occasionally. I dont really get why, I thought it could be about the lateinit so I change it to a nullable variable (despite the fact there is no "lateinit exception"). Is that correct?

[Animesh Sahu]

I think you want to use val list get() = aLiveData.value

[Animesh Sahu]

Accessing variable which isn't initialized is not permissible, you'll get PropertyNotInitializedException, though don't know how you got the NPE instead.

[KayCee]

thank you, but why can't I define
val list = someLiveData.value directly?

[Animesh Sahu]

It creates a field and initialize it to someLiveData.value which doesn't exist at the time of creating variable list

[Animesh Sahu]

val list get() = aLiveData.value is basically like a function and doesn't have any field in it, you can think of it as fun getList(): List<...> = someLiveData.value

[KayCee]

I think the full version shoud be
val list: <DataTye>
get () =...
so backing properties in kotlin is something like you create a not null list and initialize it to a value?

[KayCee]

I changed it like this:
var aLiveData: LiveData<List<T>>? = null
then
val list = aLiveData?.value
shoud be no prob now?

[Animesh Sahu]

list won't be changed when livedata changes, it'll always be null.

[Animesh Sahu]

it "stores" the result at the time it is initialized

[Animesh Sahu]

See: Properties: Getters, Setters, const, lateinit - Kotlin Programming Language

[KayCee]

I mean
var aLiveData: LiveData<List<T>>? = null
aLiveData = getDataFromDb()
val list = aLiveData?.value

[Animesh Sahu]

I don't know how does that work, are you declaring property in a class or a variable in a function?

[Animesh Sahu]

Before seems like in a class, but now in a method as you are calling a function in the next line

[KayCee]

😂 sorry that 3 sentences are in 3 different positions in my ViewModel. It works now btw thank you very much for your help. I just can't know why it is NPE. Sadly that I can't reproduce the bug

[Animesh Sahu]

blob thinking upside down