The class cannot inherit from the AndroidViewModel, why?

问题

I try create a new class that inherits from AndroidViewModel, like this

public class LoginViewModel extends AndroidViewModel {

       public LoginViewModel() {}
...

But I get this message in the ide:

There is no default constructor available in 'android.arch.lifecycle.AndroidViewModel'

My happen this?

My graddle looks like this:

...
    implementation 'android.arch.lifecycle:extensions:1.1.1'
...

Any idea?

Thanks

回答1:

You will need to add super call to AndroidViewModel class when inheriting from it. AndroidViewModel class contains default constructor having Application class as variable, so you should change your implementation as below :

public class LoginViewModel extends AndroidViewModel {

   public LoginViewModel(Application application) {
       super(application);
       // Do rest of your stuff here ...
   }
...

---

Default implementation of AndroidViewModel class states that :

Application context aware ViewModel.

Subclasses must have a constructor which accepts Application as the only parameter.

回答2:

AndroidViewModel has only one public constructor that takes an Application as parameter. You must call this from your constructor:

public LoginViewModel(Application app) {
    super(app);
}

回答3:

https://developer.android.com/reference/android/arch/lifecycle/AndroidViewModel

Subclasses must have a constructor which accepts Application as the only parameter.

来源：https://stackoverflow.com/questions/54462295/the-class-cannot-inherit-from-the-androidviewmodel-why