Activities and Fragments

Question 1

Why extend AppCompatActivity?

Answer 1

AppCompatActivity is a subclass of Activity that supports all modern Android features while providing backward compatibility with older versions of Android.

Question 2

What does AppCompatActivity.setContentView( ) do?

Answer 2

Specifies AND inflates the layout xml associated with an Activity

Question 3

What is the name of the bar featuring clock, battery, signal etc

Answer 3

Status bar

Question 4

What is the difference between the following?
ActionBar
AppBar
Toolbar

Answer 4

action bar = app bar

Toolbar succeeded ActionBar in API 21 (Lollipop)
Toolbar is more customisable.
Using Toolbar in API < 21 requires
^androidx.appcompat.widget.Toolbar/^ wrapped in an ^AppBarLayout/^

Question 5

What does the navigation component enable?

Which 2 dependencies are required to use the navigation component?

Answer 5

Navigation component enables:

• Complex navigation
• Transition animation
• Deep Linking
• Compile-time checked argument passing between screens

Dependencies in build.gradle(Module:)
implementation “androidx.navigation:navigation-fragment-ktx:$navigationVersion”
implementation “androidx.navigation:navigation-ui-ktx:$navigationVersion”

Question 6

In single-activity architecture, the main activity’s layout xml only needs one element with 8 attributes. List them.

Answer 6

^fragment xmlns:android=”http://schemas.android.com/apk/res/android”

xmlns: app="http://schemas.android.com/apk/res-auto"
android: id="@+id/nav_host_fragment"  android:name="androidx.navigation.fragment.NavHostFragment"
android: layout_width="match_parent"
android: layout_height="match_parent"
app: defaultNavHost="true"
app: navGraph="@navigation/nav_graph" /^

Question 7

What objects can findNavController( ) be called on?

Answer 7

Fragment or View.

Both end up calling the function on the fragment’s root view.

Question 8

What is the syntax for navigating in code using the navController WITHOUT Safe Args?

Answer 8

findNavController( ).navigate(R.id.my_action_id)

Question 9

What attributes does a fragment need when it’s added to a nav_graph?

What optional attributes are included in Codelabs?

Answer 9

^fragment
android:id="@+id/gameFragment"
android:name="com.example.android.navigation.GameFragment"
tools:layout="@layout/fragment_game" ^
^action
android:id="@+id/..."
app:destination="@id/..."/^
^/fragment^

OPTIONAL
fragment - android:label
action - app:popUpTo=”@id/…”
action - app:popUpToInclusive=”true/false”

Question 10

If navController is required in the Activity, what is the syntax to access it?

Next, set up an action bar with a back button that uses the navController.

Answer 10

In Activity.onCreate( )
val navController = findNavController(R.id.myNavHostFragment)

To set up action bar with back button:

In Activity.onCreate( )
NavigationUI.setupActionBarWithNavController(this,navController)

After onCreate( )
override fun onSupportNavigateUp(): Boolean {
  val navController = this.findNavController(R.id.myNavHostFragment)
  return navController.navigateUp( )
}

Question 11

How should the functionality of an app bar’s back button differ from the device’s back button?

Answer 11

App bar back button:

• navigates within the app based on nav_graph
• never takes user out of app

Device back button:
- navigates back through the back stack

Question 12

What are two other names for a key-value store?

Answer 12

Dictionary

Associative array

Question 13

What is the Safe Args feature?

Why are Safe Args more reliable than bundles?

Answer 13

The feature is a gradle plugin, a feature of Android’s Navigation Architecture Component, that generates code and classes to detect arg errors at compile time.

Type mismatch / missing key errors aren’t picked up by the compiler but will throw runtime errors

Question 14

How to implement the Safe Args dependency?

Answer 14

In build.gradle(PROJECT)
dependencies{
...
classpath "androidx.navigation:navigation-safe-args-gradle-plugin:$navigationVersion"
}

In build.gradle(App)
apply plugin: ‘androidx.navigation.safeargs’

Question 15

What is the syntax for navigating in code using the navController WITH Safe Args?

Answer 15

view.findNavController().navigate(MyFragmentDirections.myNavActionId(myNavArgs))

Question 16

What is the syntax for receiving navArgs in the receiving Fragment? (2 versions)

Answer 16

val args = ReceivingFragmentArgs.fromBundle(requireArguments( ))

OR

val args: ReceivingFragmentArgs by navArgs()

Question 17

What is the difference between an explicit and an implicit intent?

Answer 17

Explicit
- send a message to a specific target

Implicit

• initiates an Activity without knowing which app or Activity will handle the task.
• requires an ACTION (eg ACTION_VIEW, ACTION_EDIT etc)

Question 18

How to build an intent in code?

Answer 18

private fun buildIntent( ): Intent {
val intent = Intent(Intent.ACTION_*)
   intent.setType("mime_type")
            .putExtra(Intent.EXTRA_*, extraParams)
   return intent
}

startActivity(buildIntent( ))

// Build and return the intent from a function so it can be checked if needed before being used to start an Activity

Question 19

How to check if an intent will resolve before using it to start an Activity?

Answer 19

if(intent.resolveActivity(requireActivity( ).packageManager) == null) {
  // handle intent not resolving
}

Question 20

How do you make it possible for an instance of a data class to be passed as an argument from one fragment to another?

Answer 20

Make it parcelable (recommended, faster)
Annotate the data class with @Parcelize
Have the data class implement the Parcelable interface

Make it serializable
Have the data class implement the Serializable interface

Question 21

What is the difference between a Bundle and a PersistableBundle?

Answer 21

A persistable bundle is more restrictive (can only contain basic Types) but is disk safe (more reliable). Apparently useful when dealing with Job Services and Job Schedulers.