Lesson 8: App architecture (UI layer)

1. To avoid losing data during a device-configuration change, you should save app data in which class?
   ViewModel

   LiveData

   Fragment

   Activity
2. A ViewModel should never contain any references to fragments, activities, or views. True or false?
   True, it should never contain any references.

   False, it should contain at least a reference to one of the above.
3. When is a ViewModel destroyed?
   When the associated UI controller is destroyed and recreated during a device-orientation change.

   In an orientation change.

   When the associated UI controller is finished (if it is an activity) or detached (if it is a fragment).

   When the user presses the Back button.
4. What is the ViewModelFactory interface for?
   Instantiating a ViewModel object.

   Retaining data during orientation changes.

   Refreshing the data being displayed on the screen.

   Receiving notifications when the app data is changed.
5. How do you encapsulate the LiveData stored in a ViewModel so that external objects can read data without being able to update it?
   Inside theViewModel object, change the data type of the data to private LiveData. Use a backing property to expose read-only data of the type MutableLiveData.

   Inside theViewModel object, change the data type of the data to private MutableLiveData. Use a backing property to expose read-only data of the type LiveData.

   Inside the UI controller, change the data type of the data to private MutableLiveData. Use a backing property to expose read-only data of the type LiveData.

   Inside theViewModel object, change the data type of the data to LiveData. Use a backing property to expose read-only data of the type LiveData.
6. LiveData updates a UI controller (such as a fragment) if the UI controller is in which of the following states?
   Resumed

   In the background

   Paused

   Stopped
7. In the LiveData observer pattern, what is the observable item (what is observed)?
   The observer method

   The data in a LiveData object

   The UI controller

   TheViewModel object
8. In which class should you add the data-formatting logic that uses the Transformations.map() method to convert LiveData to a different value or format?
   ViewModel

   Fragment

   Activity

   MainActivity
9. The Transformations.map() method provides an easy way to perform data manipulations on the LiveData and returns ___.
   AViewModel object

   A LiveData object

   A formatted String

   A RoomDatabase object
10. What are the parameters for the Transformations.map() method?
    A source LiveData and a function to be applied to the LiveData

    Only a source LiveData

    No parameters

    ViewModel and a function to be applied
11. The lambda function passed into the Transformations.map() method is executed in which thread?
    Main thread

    Background thread

    UI thread

    In a coroutine

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