How to pass custom parameters to a ViewModel using Factory?

user_8163202 0
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I am aware in order to pass custom parameters to ViewModel, we can use ViewModelProvider.NewInstanceFactory, Like this:

// Factory Class    
class MyFactory extends ViewModelProvider.NewInstanceFactory {

        private final String mId;
        public MyFactory(String id) {
            mId = id;
        }

        @NonNull
        @Override
        public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
            return (T) new MyViewModel(mId);
        }
    }


// MyViewModel class
class MyViewModel extends ViewModel {

  public MyViewModel(String id) {
     ...
  }
}

// Activity I can Initialise as: 
MyFactory modelFactory = new MyFactory(id);
viewModel = ViewModelProviders.of(this, modelFactory).get(MyViewModel.class);

How can I achieve the same with custom parameters in the AndroidViewModel subclass along with the Application context. Like

// MyAndroidViewModel class
    class MyAndroidViewModel extends AndroidViewModel {

      public MyViewModel(Application context, String id) {
         super(context);
         ...
      }
    }

How to initialise MyAndroidViewModel and how ViewModelProvider.NewInstanceFactory comes into play here?

android-architecture-components android-viewmodel android java
1 Answers

I had this problem previously and I managed it by doing this. In your activity create your ViewModel factory as below :

//Inside MyActivity
ViewModelProvider.Factory factory = new ViewModelProvider.Factory() {
            @NonNull
            @Override
            public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
                return (T) new MyAndroidViewModel(getApplication(),
                        "My string!");
            }
        };

And then use it to create your ViewModel :

viewModel = ViewModelProviders.of(this, factory).get(MyAndroidViewModel.class);

UPDATE:

As the ViewModelProviders class has been deprecated, the updated answer would be as below. The factory is the same as before, it has just changed to Kotlin.

var factory = object : ViewModelProvider.Factory {
        override fun <T : ViewModel?> create(modelClass: Class<T>): T {
            return  SimpleAndroidViewModel(activity!!.application,
                "My string!") as T
        }
    }

However, the line where we were creating the ViewModel instance has changed and now we are using the ViewModelProvider class.

private val viewModel: SimpleAndroidViewModel by lazy {
        ViewModelProvider(this, factory).get(SimpleAndroidViewModel::class.java)
    }
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