Nullable class is recognized as non-nullable, Kotlin, Android Studio-CodePudding

Maybe it's a silly question, but I've been thinking about it the whole morning. I try to get data from another activity via Register activity result using a nullable class, but Kotlin sees it as a nonnullable class and doesn't allow me to use

it.data?.getSerializableExtra

it.data!!.getSerializableExtra

with it. When I press a button that launches this launcher the app crashes.

var userData = UserDat()

... 
onCreate(){ 

editLauncher = registerForActivityResult(ActivityResultContracts.StartActivityForResult()) {
                if (it.resultCode == RESULT_OK) {
                    userData = (it.data?.getSerializableExtra("userdata") as UserDat)
                    binding.apply {
                        tvUserAge.text = userData.age.toString()
                        tvUserHeight.text = userData.height.toString()
                        tvUserWeight.text = userData.weight.toString()
                    }
                } 
} 

        binding.btEditData.setOnClickListener() {
            editLauncher?.launch(Intent(this@Profile, MeasurmentsEditor::class.java))}

}

      *** Called Activity: ***

var dataSending = UserDat() ... onCreate(){ binding.btMeasureDone.setOnClickListener(){

dataSending.age = 16.0
    dataSending.height = binding.edHeight.text.toString().toDouble()
    dataSending.weight = binding.edWeight.text.toString().toDouble()

val editIntent = Intent().apply { putExtra("userdata", dataSending) } setResult(RESULT_OK, editIntent) finish()}



```   *** Class File: ***
class UserDat(var age:Double? = null, var height:Double? =null, var weight: Double? = null ):Serializable

Error text:

 Caused by: java.lang.NullPointerException: null cannot be cast to non-null type com.example.appname.UserDat
        at com.example.appname.Profile.onCreate$lambda-2(Profile.kt:38) /*38th line is 
userData = (it.data?.getSerializableExtra("userdata") as UserDat) */

I tried to create another class, copying it from another nullable class

class UserMeasurements(var neck:Double? = null, var shoulders:Double? = null, var chest:Double? = null):Serializable

without even changing variable names, but it still didn't work, though another registerActivityForResult that uses UserMeasurements works fine.

Rebuilding project didn't work either.

P.S. pls don't downgrade me, I'm just 16

CodePudding user response：

var userData = UserDat() implicitly tells the compiler to treat userData as not-nullable of type UserData since the compiler tries to declare each variable as minimal required type. Since nullable types are broader than not-nullable, they are not chosen by compiler. I believe it is like that because not-nullable types are easier to process in terms of following code constructions.

As was already mentioned, var userData: UserDat? = UserDat() will explicitly tell the compiler to treat userData as nullable type.

CodePudding user response：

The line it.data?.getSerializableExtra("userdata") checks if data is not null and then gets the serializable data and casts it to UserData. if the data is null it puts null in the userdata field because you don't handle the null case.

Since you want to use a nullable value in the userdata just change this line:

`var userData = UserDat()`

to:

var userData: UserDat? = UserDat()

This specifies that your UserDat object can hold null values.

CodePudding user response：

You have to use UserDat?

userData = (it.data?.getSerializableExtra("userdata") as UserDat?)

If you have null in you value, you need cast you value in class with <className>?