Hey guys, for the sake of studying, I am digging i...

# android

[Ofir Bar]

Hey guys, for the sake of studying, I am digging inside the code of the abstract class LiveData .
I wonder, why can’t I call postValue or setValue If I subclass a LiveData?

private val someInstanceOfLiveData = object : LiveData<String>(){}

fun test(){
    someInstanceOfLiveData.setValue() // Cannot access 'setValue': it is protected/*protected and package*/ in '<no name provided>'
    someInstanceOfLiveData.postValue() // Cannot access 'postValue': it is protected/*protected and package*/ in '<no name provided>'
}

from my understanding, object : LiveData<String>(){} is a subclass of the abstract LiveData class.

If it is a subclass, why can’t I call postValue()/setValue(), which are declared as protected inside the LiveData?

[Samme Kleijn]

LiveData is immutable, use MutableLiveData

[Ofir Bar]

@Samme Kleijn This does not answer my question.
I know MutableLiveData is a subclass of LiveData .

But why I can’t subclass LiveData and call postValue/setValue on it?

[Adam Powell]

Only the subclass itself can call protected methods. You're trying to call the mutator methods from outside.

[Adam Powell]

@Samme Kleijn LiveData is read-only, not immutable. It can change, but it doesn't expose permission to change it.

[Samme Kleijn]

Sorry, made a mistake, indeed I meant read-only.

[Ofir Bar]

Hey @Adam Powell
“Only the subclass itself can call protected methods”

Isn’t my anonymous object a subclass of the LiveData too?

So do you mean that only the fact that I call it outside of the androidx.lifecycle package is what blocking me?

[Adam Powell]

No, what's blocking you is that you're trying to call it from outside of your subclass declaration - you can only call them inside the {} that comes after your object : LiveData<String>(). You're trying to call them from outside, which would break encapsulation of protected.

[Ofir Bar]

Ohhhhh now I get it! so what MutableLiveData does is just taking the postValue() and setValue(), and overriding it simply for the sake of making the methods public.

I did something similar now:

private val someInstanceOfLiveData = object : LiveData<String>(){

    public override fun setValue(value: String?) {
        super.setValue(value)
    }

    public override fun postValue(value: String?) {
        super.postValue(value)
    }

}

fun test(){
    someInstanceOfLiveData.setValue("")
    someInstanceOfLiveData.postValue("")
}

Thank you my friend 🙂 🍕🍻
@Adam Powell