android - What is the 1:n relationship between view and viewModel

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I know view and viewmodel are 1:n. However, in most examples there was one viewmodel per activity. ex) mainActivity - mainViewModel , userListActivity - userListViewModel

Shouldn't it be like below if it's a 1:n relationship?? ex) mainActivity - viewModel , userListActivity - viewModel

What does 1:n mean? Does it mean n activities in one viewmodel? Does it mean n xml files in one viewmodel?

mvvm android
1 Answers

Yes the common use-case is 1:1. But theoretically you could have multiple ViewModels serving a view, so that's why the 1:n relation.

In practice this could be useful if you'd like to share a ViewModel between two views for example, or when you have a shared Flow ViewModel

So basically in that flow every View could communicate with two ViewModels: the shared one and one specific for that view:

  • Imagine a SignUp flow, with two screens user credentials (email, password, etc...) and another one with some preferences (like membership, notification, address or other app specific settings)
  • In this case the SharedFlowViewModel could hold all the user information, and at the last screen the Submit will send the request. All other screens with the individual ViewModels would just handle the individual screen logic: form validation, input enabling/desabling, etc...
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