Question: What is the use of ViewModel in Android?

What is the purpose of ViewModel in Android?

The purpose of the ViewModel is to acquire and keep the information that is necessary for an Activity or a Fragment. The Activity or the Fragment should be able to observe changes in the ViewModel. ViewModels usually expose this information via LiveData or Android Data Binding.

How do you use a ViewModel?

There are three steps to setting up and using a ViewModel:

  1. Separate out your data from your UI controller by creating a class that extends ViewModel.
  2. Set up communications between your ViewModel and your UI controller.
  3. Use your ViewModel in your UI controller.

What is the difference between ViewModel and Android ViewModel?

The difference between the ViewModel and the AndroidViewModel class is that the later one provides you with an application context, which you need to provide when you create a view model of type AndroidViewModel.

How do you use ViewModel in Kotlin?

In order to use ViewModel, add a dependency on androidx. lifecycle’s lifecycle-viewmodel-ktx library in your module’s build. gradle file and sync the changes. For every Activity or Fragment, whose data you want to preserve using ViewModel, creating a separate class is highly recommended.

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Can we pass context to ViewModel?

It’s not a good practice to pass your Activity Context to the Activity’s ViewModel as its a memory leak. Hence to get the context in your ViewModel, the ViewModel class should extend the Android View Model Class. That way you can get the context as shown in the example code below.

How do I clear ViewModel data on Android?

As stated by @Nagy Robi, you could clear the ViewModel by call viewModelStore. clear() . The problem with this is that it will clear ALL the view model scoped within this ViewModelStore . In other words, you won’t have control of which ViewModel to clear.

What is the use of ViewModel?

The purpose of ViewModel is to encapsulate the data for a UI controller to let the data survive configuration changes. For information about how to load, persist, and manage data across configuration changes, see Saving UI States.

What should ViewModel contain?

The simplest kind of viewmodel to understand is one that directly represents a control or a screen in a 1:1 relationship, as in “screen XYZ has a textbox, a listbox, and three buttons, so the viewmodel needs a string, a collection, and three commands.” Another kind of object that fits in the viewmodel layer is a …

What is the difference between model and ViewModel?

A model is usually more closely related to how your data is stored (database, services, etc.) … The ViewModel on the other hand is closely related to how your data is presented to the user. It is usually a flatten version of your model, denormalized, etc. It can be the aggregation of multiple models.

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Can a ViewModel contains other ViewModels?

Having a master ViewModel with several child ViewModels is very handy if you have a complex UI. The main ViewModel may be responsible for handling the top level UI controls and for coordination of the child VMs, while other ViewModels are responsible for communication with the sub regions of your UI.

CAN A activity have multiple ViewModels?

You should have one ViewModel per View (Activity, Fragment or Custom View), with multiple LiveData, one for each logical unit. … However, even google suggests that you may have more than one view model.

Who creates the instance of a ViewModel?

As the library is the one responsible for creating the ViewModel, we do not get to call its constructor, the library is doing that internally, and by default it will always call the empty constructor, making it impossible to pass data to it.