Skip to main content

Why the ViewModel is now a must


Inspired by Lyla Fujiwars latest post, ViewModels with Saved State, Jetpack Navigation, Data Binding and Coroutines, I decided to list some of the reasons why the ViewModel is strongly suggested to be used on the Android app.


1. Views are independent

The ViewModel does fully respect the Single Responsibility Principle, leaving the Activity/Fragment do its thing. When the ViewModel is included,  views are passive and just wait for changes without actually doing anything. This is done through LiveData or RxJava, which provide observable fields: 


The MutableLiveData is the variable we are prepared that it might take changes of the value asigned during the flow. And giving its value to the live data means that whatever happens that variable value LiveData is going to observe it. 
After that, the Fragment/Activity just waits for that variable: 

If you notice, the view does nothing except handles the child views.

2. Presenter destroyed

I don't want to be rude with people using the MVP architecture, but I think the ViewModel removes lots of boilerplate code as well as the view reference from the presenter. MVP done wrong could just lead us to complex architecture apps. However, the Android team strongly suggests using the presenter behind the ViewModel if you have lots of business logic to deal with and infinite number of if and else blocks. 

3. onSavedInstanceState is not a pain anymore

If you check the article on the introduction, the latest version of Android Architecture components has brought a nice support over the onSavedInstanceState. You will now deal with it on the ViewModel, and only instantiating it on the Activity/Fragment

Note, below gists not original, brought from the article above

And now a simple case for restoring some userId:

That's simply because the ViewModel deserved more to deal with the onSavedInstanceState than the views, plus it has a different lifecycle which makes it survive the configuration change.

4. Can be used to share data between fragments

And I love it lot. ViewModels can be easy integrated to share data between fragments, removing once and for all the broken telephone way of EventBuses, perhaps static variables or some unnecessary SharedPreferences calls.

5. Easy integration with Coroutines

And my favorite part. The Android team has introduced us with an extension function for the ViewModel called viewModelScope. What is does is basically gives a CoroutineContext that handles lifecycle without need to override the onCleared method to cancel the job. That way, you don't have to be scared of memory leaks and perform coroutine actions easily. For more information, please head over to my other post about Usage of the ViewModelScope .

Conclusion
In my own opinion, the ViewModel has been the missing peace which corrected lots of admitted mistakes by the Android team. Android apps without a ViewModel don't suck, they are all awesome and each developer needs to be congratulated for building apps, but the ViewModel makes life easier. There are lots of other reasons, and really important ones. For example the Databinding, but their logic can be achieved even without ViewModel also, that's why I haven't included it in the post.

Popular posts from this blog

Modularizing your Android app, breaking the monolith (Part 1)

Inspired by a Martin Fowlers post about Micro Frontends, I decided to break my monolithic app into a modular app. I tried to read a little more about breaking monolithic apps in Android, and as far as I got, I felt confident to share my experience with you. This will be some series of blog posts where we actually try to break a simple app into a modularized Android app.

Note: You should know that I am no expert in this, so if there are false statements or mistakes please feel free to criticize, for the sake of a better development. 

What do you benefit from this approach:
Well, people are moving pretty fast nowadays and delivery is required faster and faster. So, in order to achieve this, modularising Android apps is really necessary.You can share features across different apps. Independent teams and less problems per each.Conditional features update.Quicker debugging and fixing.A feature delay doesn't delay the whole app. As per writing tests, there is not too much difference about…

From Gson to Moshi, what I learned

There is no doubt that people are getting away from GSON and I agree with those reasons too. The only advantage GSON has over other parsing libraries is that it takes a really short amount of time to set up. Furthermore, the most important thing is that Moshi is embracing Kotlin support.

First let's implement the dependency:
implementation("com.squareup.moshi:moshi:1.8.0") It's not a struggle to migrate to Moshi. It's really Gson look-a-like. The only thing to do is annotate the object with @field:Json instead of @SerializedName (which is Gsons way for JS representation):

data class User( //GSON way @SerializedName("name") val name: String, @SerializedName("user_name") val userName: String, @SerializedName("last_name") val lastName: String, @SerializedName("email") val email: String ) data class User( //Moshi way @field:Json(name = "name") val name: String, @field:Json(name = "user_name…

Modularizing your Android app, breaking the monolith (Part 2)

This is part 2 of a series of articles about modularizing Android app. If you haven't yet read the first article, you may find it here.

On our first article we just moved some classes outside the application and applied as an independent module. But what if we have dependencies pulled from the application level? This could be a small challenge. First of all, we want to clarify on how are we going to modularize the app. And depending on the previous article, I chose the by feature version of modularization. First of all, let's show some dependencies that are going to be needed in the whole app.

Note: I'm using Dagger for handling dependencies but manual DI or any dependency tool should be fine to understand this part.

So, this is my dependency schema:


Well, it's not that bad, but this isn't what we want to transform to when trying to modularize the app. If you think about it, modules that don't need a dependency, can get it quite easily. For example: A FeatureXVi…