获取ViewModel ViewModelProvider.Factory和应用程序上下文

Question

I am extending AndroidViewModel to get an application context in my ViewModel but Now I also want to pass some parameters to my ViewModel. After some google search, I came to know that I can use ViewModelProvider.Factory to get Parametrized constructor of my MyViewModel but how to get an application context.

Thanks in advance.

Answer 1

You would need an Application in ViewModel.Factory to instantiate an AndroidViewModel .

Ways to achieve this

• if you are instantiating the ViewModel in your Activity/Fragment then do getApplicationContext() and cast it as Application . If in fragment you can get the hosting Activity and get Application from it.

// Kotlin code
viewModel = ViewModelProviders.of(this,
                ViewModel.Factory(activity?.application!!, param1, param2)) // from an fragment onViewCreated()

• if your app has an Application class expose an method to get an application instance.

// JAVA code
public static Application getApp() {
        return YourApplication.instance; // instance will be an static field in Application class
    }

Answer 2

From your activity you can use:

Kotlin:

applicationContext

Java:

getApplication().getApplicationContext()