Android Development

Question 1

What are the 4 types of app components?

Answer 1

Activities.
Services.
Broadcast receivers.
Content providers.

Question 2

What is an Activity lifecycle?

Answer 2

https://developer.android.com/reference/android/app/Activity.html

Launched -> onCreate -> onStart -> onResueme -> Running -> onPause -> onStop

onPause -> onResume
onStop -> Killed or onStop -> onRestart

Question 3

What is an Intent?

Answer 3

A messaging object you can use to request an action from another app component.

Question 4

What are the three fundamental use cases of an intent?

Answer 4

• starting an activity
• starting a service
• delivering a broadcast

Question 5

Should an implicit intent be used when starting a service?

Answer 5

No

Question 6

Why should you use an explicit intent to start a service?

Answer 6

Security reasons, and if an implicit intent is used, your app doesn’t have control of which service will respond to the intent. (API 21+) throws exception if using an implicit intent on call ‘bindService()’

Question 7

What are the main component of building an Intent?

Answer 7

Component name, Action, Data, Category, Extras, Flags

Question 8

How do components receive intents?

Answer 8

Declaring one or more intent filters for each of the app components with an element in the manifest file.

Question 9

Which three tests must a intent filter pass for implicit intent to use that component?

Answer 9

Action test, Category test, Data test

Question 10

Can you declare multiple per component?

Answer 10

Yes

Question 11

Which object has a set of query methods that will return all components that accept a particular intents? (by checking components )

Answer 11

PackageManager

Question 12

What class serves ass the entry point for an app’s interaction with the user?

Answer 12

Activity class

Question 13

Where must you declare activities that will be used in your application?

Answer 13

in the manifest file.

Question 14

What is the only required attribute for declaring an activity in the manifest?

Answer 14

android:name attribute

Question 15

Which Activity callback method is called when the system first creates the activity?

Answer 15

onCreate()

Question 16

What should be performed in the onCreate method of an Activity?

Answer 16

Basic application startup logic, (example, bind data, initialize background threads, instantiate class-scope variables).

Question 17

Describe an Activity ‘onStart()’ method?

Answer 17

Prepares the activity to enter the foreground and become interactive. (ex. app initializes code that maintains UI, or register a BroadcastReceiver that monitors changes that are reflected in the UI).

Question 18

Describe an Activity ‘onResume()’ method?

Answer 18

When this method is executed, activity enters foreground, and is the state in which the app interacts with the users. (Initialize components that are released during ‘onPause()’).

Question 19

When does the Activity leave the onResume state?

Answer 19

When the app loses focus.

Question 20

What Activity method is called when the app loses focus?

Answer 20

onPause()

Question 21

Describe an Activity ‘onPause()’ method?

Answer 21

Execution is very brief, and does not afford enough time to perform save operations or any long operation.

Question 22

What Activity method should be used for ‘heavy-load’ shutdown operations?

Answer 22

onStop()

Question 23

Once an Activity is in the ‘onPause()’ state, how long does the activity remain in the ‘onPause()’ state?

Answer 23

Until either the activity becomes completely invisible to the user, or if the activity resumes, and the system invokes the ‘onResume()’ method.

Question 24

When an Activity is no longer visible to the user, what method is invoked?

Answer 24

onStop()

Question 25

Describe an Activity ‘onStop()’ method?

Answer 25

Occurs when an activity becomes invisible to the user, and is the callback to release resources that aren’t needed. (ex. if registered a BroadcastReceiver in onStart() then unregister the receiver in the onStop())

Question 26

What Activity callback method is called after onStop()?

Answer 26

onDestroy()

Question 27

Describe an Activity ‘onDestroy()’ method?

Answer 27

It is the final call the activity receives. The system invokes this callback because the activity is finishing due to isFinishing() being called or the system destroys the process.

Question 28

What is the purpose of the Activity ‘onDestroy()’ method?

Answer 28

To release all resources that have not yet been released.

Question 29

What Activity callback is called when expecting a result from an Intent?

Answer 29

onActivityResult(int, int, Intent)

Question 30

Can the android system destroy the process containing your activity to recover memory if the activity is in the Stopped state?

Answer 30

Yes, especially when it hasn’t been used in a long time, or if the foreground activity requires more resources.

Question 31

If an Activity is destroyed by the system, and the user navigates back to the activity, how is previously destroyed state get stored?

Answer 31

instance state is a collection of key-value pairs stored in a Bundle object

Question 32

What happens to an activity when a configuration change occurs?

Answer 32

The activity is destroyed and recreated.

Question 33

What is a Task?

Answer 33

It’s a collection of activities that the users interact with when performing a certain job. (ex. using an application)

Question 34

Does the Android system retain state of every activity in the task, when the task is in the background?

Answer 34

Yes, unless the android system needs to remove resources for memory.

Question 35

When an activity is destroyed, the system does not retain the activity’s state?

Answer 35

True

Question 36

What is the difference in life cycle between AsyncTask and a Loader?

Answer 36

An AsyncTask lives as longs as the task lives, the Loader lives as long as the activity that starts it. Loaders are tied to the activity life cycle.

Question 37

How can you make a string resource untranslatable?

Answer 37

By setting attribute ‘translatable’ = false

Question 38

Where should your application activities be declared?

Answer 38

AndroidManifest.xml file

Question 39

How can you pass multiple parameters to AsyncTaskLoader?

Answer 39

By passing the extra parameters to the constructor