[jetpack]: AndroidViewModel在自定义ViewMode中继承自AndroidViewModel，

在自定义ViewMode中继承自AndroidViewModel，创建实例需要做如下修改。

MyViewModel.java

public class MyViewModel extends AndroidViewModel {
    public MyViewModel (@NonNull Application application) {
        super(application);
    }
}

MainActivity.java

public class MainActivity extends AppCompatActivity { 
   MyViewModel model;   
   @Override    
   protected void onCreate(Bundle savedInstanceState) { 
       super.onCreate(savedInstanceState);     
       setContentView(R.layout.activity_main);  
       // - model = new ViewModelProvider(this).get(MyViewModel.class);
       // + model = new ViewModelProvider(this, ViewModelProvider.AndroidViewModelFactory.getInstance(getApplication())).get(MyViewModel.class);
}