视图模型工厂 class 在更新生命周期版本后不起作用

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

that is deprecated right now so you Can use - ViewModelProvider.AndroidViewModelFactory() - instead of it. and this is the link from the documentation https://developer.android.com/reference/androidx/lifecycle/ViewModelProviders