MVVM 架构 Android

Question

I have one Activity and i have created one View-model for it. I have created different classes like UiUtil( show, hide view, hide key board ), Network layer, Data Base layer, AppUtil( for common functionality like Collection check, String validation, Date Conversion etc)

My question is, In MVVM design pattern is Activity can use these utility classes directly or it needs to use these classes via View-model, if it via view model then in the view-model i have to write a method that just call utility classes method. like below TimeDateManager is utility class used in view-model class HomeViewModel: BaseViewModel() { fun prepareTimeAmPmToDisplay(context: Context, alarm: Alarm): String { return TimeDateManager.prepareTimeAmPmToDisplay(context, alarm) } }

Answer 1

Architectures are not obligatory, they are recommendational, thus you can change their usage in quite wide range. The only stopper should be a common sense(if it is present of course).

In this particular case the usage of utility class inside an Activity maybe ok, based on your ViewModel construction and its way of communication with View (read Activity ).

For example if you have some LiveData that sends some kind of event(for ex. data loaded from backend or alarm trigger) inside your ViewModel and your View listens to it, I think it is ok to use util classes inside an Observer in Activity . Especially if this utils method doesn't depend on any ViewModel or Repository data. The direct utils usage in Activity is not limited by this usecase, though - there are plenty of others.

I understand that this may be an unpopular opinion in modern time of "clean approach" but I believe that this "clean approach" sometimes complicates stuff where it shouldn't, thus if mixing things a bit does not brake overall architecture but rather makes some thing more readable and easy to maintain - I would go for it.

Hope it helps.

Answer 2

My approach toward MVVM is simple, ViewModel is responsible for business logic, dealing with repositories (Network, Database, etc.) and all of the non-UI codes preparing the required data for UI, just like the documentation :

A ViewModel object provides the data for a specific UI component, such as a fragment or activity, and contains data-handling business logic to communicate with the model. For example, the ViewModel can call other components to load the data, and it can forward user requests to modify the data. The ViewModel doesn't know about UI components, so it isn't affected by configuration changes, such as recreating an activity when rotating the device.

On the other hand, ViewModels should not store a context (ApplicationContext is exceptional) and it's preferred that they do not use android APIs at all, so they become more testable (especially in the case on pure unit tests).

Also we are recommended to make use of LiveData in ViewModels and the UI has to observe the LiveData. For example, in onCreate of your Activity, you will call loadMainContent() method from VM, it calls getMainContent(page=1) from repository, and the repository will decide to load data from DB or network, and the result will be set on a LiveData were the View is listening for changes.

TL;DR

Sometimes it's even better to call these utilities from View rather than the VM. I'm pretty sure about your UiUtil also I think TimeDateManager is more view related rather than logic related. In addition, Network and DB layers are more efficient if called through a repository (which is responsible for caching, etc.) and VM can use that repo.