Question regarding delegation of Viewmodel property(Android)(Kotlin)-CodePudding

Whenever I am trying to delegate my viewmodel using the delegated property in my Fragments

val viewModel:NewsViewModel by activityViewModels<> { }

This is the error I would receive.

Property delegate must have a 'getValue(BreakingNews, KProperty*>)' method. None of the following functions are suitable.
    Lazy<NewsViewModel>.getValue(Any?, KProperty<*>)   
    where T = NewsViewModel for inline operator fun <T> Lazy<T>.getValue(thisRef: Any?, property: 
    KProperty<*>): T defined in kotlin

However, instantiating the viewmodel instance in the MainActivity this way, seems fine

val viewmodelFactory = ViewModelProviderFactory(dataRepo)
viewModel = ViewModelProvider(this,viewmodelFactory).get(NewsViewModel::class.java)

I assumed at first it may be due to the viewmodelFactory which is as follows.

class ViewModelProviderFactory(val Repo:NewsRepository): ViewModelProvider.Factory {
override fun <T : ViewModel> create(modelClass: Class<T>,extras: CreationExtras): T {

    return NewsViewModel(Repo) as T
}
}

The code below are the properties in my ViewModel, This is odd as I have cross-referred from multiple sources including the official `docs.

var breakingNews: MutableLiveData<Resource<ArticleList>> = MutableLiveData()

  var breakingNewsPage = 1
  var breakingNewsResponse: ArticleList? = null
  var searchNews: MutableLiveData<Resource<ArticleList>> = MutableLiveData()
  var searchNewsPage = 1
  var searchNewsResponse: ArticleList? = null
  var savedNumerics = 0

  var _status = MutableLiveData<String>()
  ....
    }

CodePudding user response：

Usually, you want just val viewModel:NewsViewModel by activityViewModels().

In your case, with val viewModel:NewsViewModel by activityViewModels<> { }, you skipped two things.

First, you are attempting to provide a value for the extrasProducer parameter to the activityViewModels() function. However, that lambda expression needs to evaluate to a CreationExtras object, and yours evaluates to Unit.

Second, you failed to provide a type. AFAIK, <> is not going to be valid syntax here. Either leave the <> off (and the compiler should infer the type from the property type) or fully qualify it as <NewsViewModel>. I think this is the cause of your specific syntax error, but even if you fix this, you should then run into a problem with your empty lambda expression.