Android Fragments, and Live data

Question 1

What is a fragment (2)

Answer 1

• they are reusable components of a UI and an be used in different activities
• They are modular components of an activity

Question 2

What are two key things that fragments enable you to do

Answer 2

1.Separate the navigation components from the content
2. Modifythe appearance of an activity at runtime

Question 3

What library support fragments

Answer 3

Androidx.fragment

Question 4

What are the key lifecycle stages for a fragment

Answer 4

{onAttach}
onCreate(Context context)
onCreateView(Bundle, savedInstanceState)
onViewCreated(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) - create the fragment’s view hierarchy. It is similar to onCreate, but it is responsible only for the view inflation
onViewStateRestored
onStart
onResume
onPause
onStop
onSavedInstanceState
onDestroyView
onDestroy
{onDetach}

Question 5

What are the advantages (2) and disadvantages of fragments (1)

Answer 5

• code reuse and modularity
• ability to build multi-pane interfaces (useful for tablets)
• Disadvantage is the increased code complexity

Question 6

Do fragments need to include a container,if so what is the recommended one?

Answer 6

Yes - this is in the layout file.
yes, it makes management easier. Most common is the FragmentContainerView

Question 7

How would you set up the code to use fragments

Answer 7

1. Create a fragments layout file and class
2. Add a fragments container to the the activities layout (FragmentContainerView)
3. Get a FragmentManager instance using getSupportFragmentManager()
4. Create a fragments instance
5. Commit the transaction
6. Communicate between fragments

Question 8

How are fragments loaded

Answer 8

using the FragmentManager and FragmentTransaction

Question 9

What is the Fragment manager responsible for

Answer 9

Attaching fragments to the host activity and detaching them when they are no longer in user

Question 10

How is data passed between fragments

Answer 10

Using LiveData

Question 11

What is LiveData and what does it allow

Answer 11

Architecture component in Android JetPack that implements the Observer pattern.
- permits observers to subscribe to updates for data held by the LiveData object and then when it changes they are notified
- it only updates observers that are in the active lifecycle state

Question 12

How can LiveData be implemented

Answer 12

A fragment or activity class can implement the Observer interface and be informed of changes in the observable objects

Question 13

What is ViewModel, what is it’s job, is it destroyed?

Answer 13

Architecture component of jetpack
It manages and prepares data for a fragment or an activity
It is not destroyed, it retains the data when an activity or fragment is destroyed

Question 14

How do LiveData and ViewModel fit together

Answer 14

LiveData is created as an instance within the View model class.

Question 15

What is the difference between LiveData and MutableLiveData (4 key points)

Answer 15

LiveData is an abstract class and can not be instantiated
MutableLiveData extends Livedata (and is not abstract)
MutableLiveData has two methods to modify its data setValue and postValue
The ViewModel only exposes the immutable LiveData Objects to the observers

Question 16

What are the steps to using LiveData

Answer 16

1. Add implementation to build.gradle for androidx lifecycle viewModel and livedata
2. Create ViewModel class to provide access to LiveData
3. Create an instance of MutableLiveData so we can update the data by calling the setValue method of MutableLiveData
4. Add the getText() to get the LiveData
5. Use ViewModelProvider to get an instance of ViewModel to access the LiveData
6. Make the main activity an observer and attach the observer object to the LiveData object
7. Use ViewModel Provider to get an instance of ViewModel to access the LiveData
8. Update the LiveData

Question 17

What is the Recycler View and when is it recommended

Answer 17

ViewGroup
used for displaying lists of data
recycles it’s view for displaying new items

• Recommended when the size of the data is large and there is scrolling
• & when the data frequently changes

Question 18

What does the RecyclerView Adapter do

Answer 18

Provides methods to create ViewHolder objects as needed and bind them with data

Question 19

What are the steps to use the Recycler view

Answer 19

1. add the Recycler View library to build.gradle
2. In the activity_main.xml add a RecyclerView Widget
3. Create a custom XML file with the views to be displayed in each of the rows of the Recycler view
4. define a model class that deals with the data
5. Define an adapter subclass that extends the RecyclerView.Adapter
6. Implement a nested ViewHolder class
7. Override methods in the RecyclerView.Adapter
8. Use the onCreateViewHolder method to create and Initialise the ViewHolder
9. Implement the onBindViewHolder
10. Add getItemCount to return the size of your dataset
11. instantiate the Recycler view in the activity and set an adaptor for it
12. Create a layout manager and apply it to the recyclerView
13. To reflect the updates to the data in the RecyclerView call the notifyDataSetChanged() method

Question 20

Do you need to create a FragmentManager?

Answer 20

No, the FragmentManager is not a standalone object, but rather tied to the activity or fragment’s lifecycle.

It’s automatically created and destroyed along with the activity or fragment.
You don’t need to worry about creating it yourself, just access it using the provided methods.