viewmodel factory class doesn't work after update lifecycle version

Question

I was using def lifecycle_version = "2.3.1" ,

implementation("androidx.lifecycle:lifecycle-viewmodel-ktx:$lifecycle_version") .

but I had to update version to def lifecycle_version = "2.4.0-alpha03" to use some features, but ViewModelProvider.Factory class doesn't work after I use def lifecycle_version = "2.4.0-alpha03".

class ViewModelFactory(private val param:String,private val param2: String) : ViewModelProvider.Factory {
    override fun <T : ViewModel?> create(modelClass: Class<T>): T {
        return if (modelClass.isAssignableFrom(ReviewViewModel::class.java)) {
            ReviewViewModel(param,param2) as T
        }else if(modelClass.isAssignableFrom(FoodViewModel::class.java)){
            FoodViewModel(param,param2) as T
        else {
            throw IllegalArgumentException()
        }
    }
}

the error messages are

! Class 'ViewModelFactory' is not abstract and does not implement abstract member public abstract fun <T : ViewModel> create(modelClass: Class<T>): T defined in androidx.lifecycle.ViewModelProvider.Factory

! 'create' overrides nothing

Thanks..

Answer 1

You've written:

override fun <T : ViewModel?> create(modelClass: Class<T>): T {

But what the error message is saying is that create must always have a non-null ViewModel type. You need to change your method signature to remove the ? that indicates nullability on your <T : ViewModel?>:

override fun <T : ViewModel> create(modelClass: Class<T>): T {

This is specifically called out in the Lifecycle 2.4 release notes:

Source-breaking change: ViewModelProvider has been rewritten in Kotlin. ViewModelProvider.Factory.create method now longer allows nullable generic.

Answer 2

I have fixed my issue with the help of above two answers, but I am just extending answer that we need to do that is

1. Remove ? that indicate nullability on your <T :ViewModel?>, as below

   override fun <T : ViewModel> create(modelClass: Class<T>): T {}
   

2. Change ViewModelProvider.Factory to ViewModelProvider.AndroidViewModelFactory()