Good day, Following are 2 weird behaviors I notice...

# koin

[aipok]

Good day,
Following are 2 weird behaviors I noticed after 3.1.0 migration… Just things that you need to be consider while declaring your classes in module…
1. Handling default parameters in the constructor are not supported/ not working, so you must declare body explicitly every time you want to declare some class which has default parameter . Otherwise you will get Declaration parameter error .
2. Second pain point I got is related to the parametersOf / params and class casting. Especially that causes error if you pass an implementation of the interface, but interface is expected as a parameter for the instance constructor. In this case params.[get|get<Something>|getOrNull] will not work, because expected T::class isn’t the parameter::class . The only way I get it to work is to use params[0] .
I assume all this could lead to confusion for people and also will take some time without a proper guidance in which case what should be used.

Added samples to thread as well for illustration purposes 👀
It could be also that I misunderstood the concept or something… in this case I would appreciate if someone who aware could give highlight for me.

[aipok]

Example for 1:
Assume I have following view model…

class SomeViewModel(
    link: LinkItem,
    private val labelWithDefaultValue: String = link.label
) : ViewModel() {
    /* Some code in here */
    fun getLabel() = labelWithDefaultValue
}

if you will define this view model in your module like this…

viewModel<SomeViewModel>()

it won’t work!
Workaround could be done from 2 ways…
you can define declaration scope more explicit like below

viewModel { params -> SomeViewModel(params.get()) }

or you can add @JvmOverloads to your ViewModel constructor

class SomeViewModel @JvmOverloads constructor(
    link: LinkItem,
    private val labelWithDefaultValue: String = link.label
) : ViewModel() {
    /* Some code in here */
    fun getLabel() = labelWithDefaultValue
}

than

viewModel<SomeViewModel>()

will work properly.

[aipok]

Example for 2:
Have sample helper class… which accept as a parameter an instance of FragmentActivity for example…

class SomeHelper(activity: FragmentActivity) {
    private val tag: String = activity::class.java.simpleName

    fun getTag() = tag
}

if declaring

factory<SomeHelper>()

and calling from SomeActivity like this

private val someHelper by inject<SomeHelper> { parametersOf(this) }

getting an error

Caused by: org.koin.core.error.NoBeanDefFoundException: No definition found for class 'class androidx.fragment.app.FragmentActivity'

Even if I’m calling like this…

private val someHelper by inject<SomeHelper> { parametersOf(this as FragmentActivity) }

resulting the same NoBeanDefFoundException error. Because in debugger the actual T::class is SomeActivity in params list.

trying to change declaration inside the module to something like this won’t work either

factory { params -> SomeHelper(params.get()) }

or

factory { params ->
        val activity = params.get<FragmentActivity>()
        SomeHelper(activity)
    }

and will cause

Caused by: org.koin.core.error.DefinitionParameterException: No value found for type 'androidx.fragment.app.FragmentActivity'

The only working solution I found so far is

factory { params -> SomeHelper(params[0]) }

[arnaud.giuliani]

yep default value in constructor can be clearly tricky, we just try to detect the primary constructor on the JVM side