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What is the use 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.
What a ViewModel should have?
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 difference between View and ViewModel?
Difference Between MVC and MVVM Design Pattern Oldest android app architecture. Multiple View can be mapped with single ViewModel and thus, the one-to-many relationship exists between View and ViewModel. The View has no knowledge about the Controller. The View has reference to the ViewModel.
What is difference between ViewModel and model?
ViewModel is the version of a Model from the business-domain layers adjusted to the specific View. It has only Properties relevant to the view and shouldn’t have methods(except simple ones like ToString() ). ViewModel is a “data container” only. A model is simply a representation of an object in your application.
Can we use ViewModel without LiveData?
Answer #1: As per Google Docs, If you are already using a library like Rx or Agera, you can continue using them instead of LiveData. But in this case, it is your responsibility to handle object allocation and de-allocation per Android components life cycle.
When to use a ViewModel in MVC application?
For example, a view may require different model data. Then in such situations like this, we need to use the concept ViewModel. A ViewModel in ASP.NET MVC application is a model which contains more than one model data required for a particular view.
Where does the concept of ViewModel come from?
This is where the concept of ViewModel arose. ViewModel is nothing but a collection of one or more models and some additional data which needs to be rendered in the view section and needs to be passed from controller to view.
How are viewmodels used in a Java program?
This ViewModel class will hold all of the data associated with the screen and have getters and setters for the stored data. This separates the code to display the UI, which is implemented in your Activities and Fragments, from your data, which now lives in the ViewModel.
What do you need to know about ViewModel in Android?
This design also means you can write tests to cover a ViewModel more easily as it doesn’t know about view and Lifecycle objects. ViewModel objects can contain LifecycleObservers , such as LiveData objects. However ViewModel objects must never observe changes to lifecycle-aware observables, such as LiveData objects.