Lesson 8: App architecture (UI layer)

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

ViewModel

LiveData

Fragment

Activity

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.

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.

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.

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.

`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

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

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

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

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

The lambda function passed into the `Transformations.map()` method is executed in which thread?

Main thread

Background thread

UI thread

In a coroutine

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

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

When is a ViewModel destroyed?

What is the ViewModelFactory interface for?

How do you encapsulate the LiveData stored in a ViewModel so that external objects can read data without being able to update it?

LiveData updates a UI controller (such as a fragment) if the UI controller is in which of the following states?

In the LiveData observer pattern, what is the observable item (what is observed)?

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?

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

What are the parameters for the Transformations.map() method?

The lambda function passed into the Transformations.map() method is executed in which thread?