Best practice for Android MVVM startActivity

Question

I am building an Android App using MVVM and DataBinding. And I have a function inside my ViewModel that starts an Activity. Is it okay to have an onClick call inside a ViewModel

Answer 1

As the principle of MVVM points out that only View (activity/fragment) holds reference to the ViewModel and the ViewModel shouldn't hold reference to any View.

In your case, to start an activity, I will do like this:

MyViewModel.class

public class MyViewModel {
public static final int START_SOME_ACTIVITY = 123;

 @Bindable
 private int messageId;

 public void onClick() {
  messageId = START_SOME_ACTIVITY;
  notifyPropertyChanged(BR.messageId); //BR class is automatically generated when you rebuild the project
 }

 public int getMessageId() {
        return messageId;
 }

 public void setMessageId(int message) {
        this.messageId = messageId;
 }

}

And in your MainActivity.class

@BindingAdapter({"showMessage"})
public static void runMe(View view, int messageId) {
    if (messageId == Consts.START_SOME_ACTIVITY) {      
        view.getContext().startActivity(new Intent(view.getContext(), SomeActivity.class));      
    }
}

@Override
protected void onPause() {
    super.onPause();
    finish(); //only call if you want to clear this activity after go to other activity
}

finally, in your activity_main.xml