30 Android Interview Questions

30 Android Interview Questions

1. What are the key components of Android Architecture?

Android Architecture consists of 4 key components:

- Linux Kernel

- Libraries

- Android Framework

- Android Applications

2. What are the advantages of having an emulator within the Android

environment?

- The emulator allows the developers to work around an interface which acts as if it

were an actual mobile device.

- They can write, test and debug the code.

- They are safe for testing the code in early design phase

3. Tell us something about activityCreator?

- An activityCreator is the initial step for creation of a new Android project. - It consists of a shell script that is used to create new file system structure required for writing codes in Android IDE.

4. What do you know about Intents?

- Notification messages to the user from an Android enabled device can be displayed

using Intents. The users can respond to intents. - There are two types of Intents -

Explicit Intent, Implicit Intent.

5. What is an Explicit Intent?

- Explicit intent specifies the particular activity that should respond to the intent. -

They are used for application internal messages.

6. What is an Implicit Intent?

- In case of Implicit Intent, an intent is just declared.

- It is for the platform to find an activity that can respond to it.

- Since the target component is not declared, it is used for activating components of other applications.

7. What do intent filters do?

- There can be more than one intents, depending on the services and activities that are

going to use them.

- Each component needs to tell which intents they want to respond to.

- Intent filters filter out the intents that these components are willing to respond to.

8. Where are lay out details placed? Why?

- Layout details are placed in XML files - XML-based layouts provide a consistent and

standard means of setting GUI definition format.

9. What do containers hold?

- Containers hold objects and widgets in a specified arrangement. - They can also hold

labels, fields, buttons, or child containers. .

10. What is Orientation?

- Orientation decides if the LinearLayout should be presented in row wise or column

wise fashion.

- The values are set using setOrientation()

- The values can be HORIZONTAL or VERTICAL

11. What is it important to set permissions in app development?

- Certain restrictions to protect data and code can be set using permissions. - In absence of these permissions, codes could get compromised causing defects in functionality.

12. What is AIDL?

- AIDL is the abbreviation for Android Interface Definition Language.

- It handles the interface requirements between a client and a service to communicate

at the same level through interprocess communication.

- The process involves breaking down objects into primitives that are Android

understandable.

13. What data types are supported by AIDL?

AIDL supports following data types:

-string

-List

-Map

-charSequence

and

-all native Java data types like int,long, char and Boolean

14. Tell us something about nine-patch image.

- The Nine-patch in the image name refers to the way the image can be resized: 4

corners that are unscaled, 4 edges that are scaled in 1 axis, and the middle one that

can be scaled into both axes. - A Nine-patch image allows resizing that can be used as

background or other image size requirements for the target device.

15. Which dialog boxes are supported by android?

Android supports 4 dialog boxes:

a.) AlertDialog: Alert dialog box supports 0 to 3 buttons and a list of selectable

elements which includes check boxes and radio buttons.

b.) ProgressDialog: This dialog box is an extension of AlertDialog and supports

adding buttons. It displays a progress wheel or bar.

c.) DatePickerDialog: The user can select the date using this dialog box.

d.) TimePickerDialog: The user can select the time using this dialog box.

16. What is Dalvik Virtual Machine?

-It is Android's virtual machine. - It is an interpreter-only virtual machine which executes files in Dalvik Executable (.dex) format. This format is optimized for efficient storage and memory-mappable execution.

17. When does onResume() method called?

onResume() method is an activity lifecycle method. This is called when the activity come to foreground. You can override this method in your activity to execute code when activity is started, restarted or comes to foreground.

18. How to launch an activity in your application?

For launching an activity, we need to create an explicit intent that defines the activity

that we wish to start. In the below code snippet, the first parameter to Intent

constructor is the current activity context and the second parameter is your new

activity class.startActivity() method can be called on Activity context.

Intent intent = new Intent(this, SecondActivity.class);

startActivity(intent);

If you want to start an activity from fragment

Intent intent = new Intent(getActivity(), SecondActivity.class);

getActivity().startActivity(intent);

19. How to define an Activity as launcher activity in application Manifest

file?

All the activities used in the application should be defined in application manifest file.

For launcher activity you need to define intent filter as shown in the below code

snippets.

<activity android:name=".MyActivity"

android:label="@string/app_name">

<intent-filter>

<action android:name="android.intent.action.MAIN" />

<category android:name="android.intent.category.LAUNCHER" />

</intent-filter>

</activity>

20. What is a ANR ?

ANR is short for Application Not Responding. Android systems shows this dialog, if application is performing too much of task on main thread and been unresponsive for a long period of time.

21. What are the measures to avoid application ANR?

ANR in application is annoying to user. It can be caused due to various reasons.

Below are some of the tips to avoid ANR

Perform all you long running network or database operation in separate thread

If you have too much of background tasks, then take it off the UI thread. You may use IntentService

Server not responding for longer period can be guilt for ANR. To avoid always define

HTTP time out for your all your webs service calls.

Be watchful of infinite loops during your complex calculations

22. What is the difference between a regular .png and a nine-patch image?

The nine patch images are extension with .9.png. Nine-patch image allows resizing that can be used as background or other image size requirements for the target device. The Nine-patch refers to the way you can resize the image: 4 corners that are unscaled, 4 edges that are scaled in 1 axis, and the middle one that can be scaled into both axes.

23. How to share text using android share Intent ?

Share intent is an easy and convenient way of sharing content of your application with

other apps.

Intent sendIntent = new Intent();

sendIntent.setAction(Intent.ACTION_SEND);

sendIntent.putExtra(Intent.EXTRA_TEXT, "This is my text to send.");

sendIntent.setType("text/plain");

startActivity(sendIntent);

24. What is the use of WebView in android?

A WebView is an android UI component that displays webpages. It can either display

a remote webpage or can also load static HTML data. This encompasses the

functionality of a browser that can be integrated to application. WebView uses the

WebKit rendering engine to display web pages and includes methods to navigate

forward and backward through a history, zoom in and out, etc.

25. Define different kind of context in android

Context defines the current state of application or object. Context provides access to

things such as creating new activity instance, access databases, start a service, etc.

You can get the context by invoking getApplicationContext(), getContext(),

getBaseContext() or this when in the activity class.

//Creating ui instance ImageButton button = new ImageButton(getContext());

//creating adapter ListAdapter adapter = new

SimpleCursorAdapter(getApplicationContext(), ...);

//querying content provider getApplicationContext().getContentResolver().query(uri,

...);

//start activity. Here this means activity context Intent intent = new Intent(this,

SecondActivity.class);

26. What are the different storage methods in android

Android offers several different options for data persistence.

Shared Preferences – Store private primitive data in key-value pairs. This sometimes

gets limited as it offers only key value pairs. You cannot save your own java types.

Internal Storage – Store private data on the device memory

External Storage – Store public data on the shared external storage

SQLite Databases – Store structured data in a private database. You can define many

number of tables and can store data like other RDBMS.

27. User interface types?

Views Notifications

28. Types of notification in android?

Tost notification

Status bar notification

Dialog notification

29. How do you find any view element into your program?

Findviewbyid

30. What is handler class do in android?

Handler allows yo to send and process message and runnable objects associated with

a thread’s message queue.