Android ListView

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Questions and Answers

What is the purpose of the android:id attribute in a ListView?

To populate the ListView with data

To set the clickable state of the ListView

To provide a unique identifier for the ListView (correct)

To specify the layout of the list items

What is the main difference between a static list and a dynamic list in Android?

The clickable state of the list

The layout of the list items

The source of the list data (correct)

The adapter used to populate the list

What is the purpose of an adapter in a ListView?

To specify the layout of the list items

To convert list data into list view items (correct)

To populate the ListView with data

To handle user clicks on the ListView

What is the default layout used for list items in a ListView?

android.R.layout.simple_list_item_1 Signup and view all the answers

What is the purpose of the android:entries attribute in a ListView?

To populate the ListView with data from a string array Signup and view all the answers

What is the method used to attach an adapter to a ListView?

setAdapter() Signup and view all the answers

What type of array is required to create an ArrayAdapter?

String array Signup and view all the answers

What is the purpose of the CursorAdapter?

To populate a ListView with data from a database Signup and view all the answers

What is the syntax to create an ArrayAdapter?

ArrayAdapter adapter = new ArrayAdapter(activity, layout, array); Signup and view all the answers

What is the purpose of the android:clickable attribute in a ListView?

To set the clickable state of the ListView Signup and view all the answers

What is the primary purpose of using an anonymous inner class in Java?

To extend a given super class or implement a given interface Signup and view all the answers

What event listener is used to respond to a single click on an item in a list view?

setOnItemClickListener Signup and view all the answers

What is the name of the method used to attach an event listener to a button in Java?

setOnClickListener Signup and view all the answers

What is the purpose of the AdapterView.OnItemClickListener interface?

To respond to a single click on an item in a list view Signup and view all the answers

What is the name of the method used to attach an event listener to a list view?

setOnItemClickListener Signup and view all the answers

What is the purpose of the ArrayAdapter class in Android?

To bind an array of data to a list view Signup and view all the answers

What is the purpose of the setOnItemLongClickListener event listener?

To respond to a long click on an item in a list view Signup and view all the answers

What is the difference between setOnItemClickListener and setOnItemLongClickListener?

One is used for single clicks and the other is used for long clicks Signup and view all the answers

What is the purpose of the ListView class in Android?

To display a list of data to the user Signup and view all the answers

What is the relationship between the ArrayList and the ArrayAdapter classes in Android?

The ArrayAdapter is used to bind an ArrayList to a list view Signup and view all the answers

What is the primary purpose of a Content Provider in an Android app?

To share data between applications Signup and view all the answers

What happens when an Activity uses too many resources in an Android app?

The Activity is destroyed to free up resources Signup and view all the answers

What is the primary purpose of an Intent in an Android app?

To pass information between applications Signup and view all the answers

What is the relationship between an Activity and its user interface in an Android app?

An Activity is a single screen with a user interface Signup and view all the answers

What happens when the user presses the Back button or destroys an Activity in an Android app?

The Activity below it is brought to the top Signup and view all the answers

What is the primary purpose of a Broadcast Receiver in an Android app?

To respond to system-wide announcements Signup and view all the answers

What is the primary purpose of a Service in an Android app?

To perform long-running operations in the background Signup and view all the answers

What is the order of Activities in the Activity Stack in an Android app?

Most recently created is at the top Signup and view all the answers

What is the primary difference between the Paused and Stopped states of an Android Activity?

The Activity instance and variables are retained in the Paused state but not in the Stopped state. Signup and view all the answers

What happens if an Android app starts an Activity that is not declared in the AndroidManifest.xml?

The compiler throws an error and prevents the app from building. Signup and view all the answers

What is the purpose of the onResume() method in an Android Activity's lifecycle?

To restore state and save state. Signup and view all the answers

What is the purpose of the onCreate() method in an Android Activity's lifecycle?

To load the UI and start and stop threads that should always be running. Signup and view all the answers

What is the primary purpose of using the Log class in an Android Activity?

To log activity methods for debugging purposes. Signup and view all the answers

What is the purpose of overriding the onPause() method in an Android Activity?

To start and stop audio, video, and animations. Signup and view all the answers

What is the purpose of registering an Activity in the AndroidManifest.xml?

To make the Activity part of the application. Signup and view all the answers

What is the purpose of overriding the onRestoreInstanceState method?

To restore the state of an Activity Signup and view all the answers

What is the purpose of calling startActivityForResult?

To get some data from another Activity Signup and view all the answers

What happens if an app is destroyed while a MediaPlayer is playing?

The MediaPlayer keeps playing Signup and view all the answers

What is the purpose of adding a new Activity to the Manifest?

To declare a new Activity to the system Signup and view all the answers

What is the purpose of calling setResult() and finish()?

To return data to the calling Activity and finish the current Activity Signup and view all the answers

What is the purpose of the onActivityResult() method?

To handle the result from a started Activity Signup and view all the answers

What is the purpose of calling startActivityForResult() and onActivityResult() together?

To get some data from another Activity and handle the result Signup and view all the answers

What is the name of the method used to restore the state of an Activity?

onRestoreInstanceState Signup and view all the answers

What happens to the state of an activity when it is paused or stopped?

It is retained, even if not in the foreground Signup and view all the answers

What is the purpose of the onSaveInstanceState method?

To save the state of an activity when it is destroyed Signup and view all the answers

What happens when an activity is destroyed under normal circumstances?

The onPause method is called, followed by onStop and onDestroy Signup and view all the answers

What is the purpose of the Bundle in onSaveInstanceState?

To store the state of an activity when it is destroyed Signup and view all the answers

What method is used to restore the state of an activity when it is recreated?

onRestoreInstanceState Signup and view all the answers

What happens to the onPauseCounter when the app is rotated?

It is saved to the Bundle and restored when the activity is recreated Signup and view all the answers

What is the relationship between the onSaveInstanceState and onRestoreInstanceState methods?

onSaveInstanceState is called when the activity is destroyed, and onRestoreInstanceState is called when the activity is recreated Signup and view all the answers

Why should the finish() and finishActivity() methods be used with caution?

Because they can affect the expected user experience Signup and view all the answers

What happens when an activity is paused?

The activity should stop animations and release resources such as broadcast receivers. Signup and view all the answers

What should an app do when it is stopped?

Save progress and restart seamlessly. Signup and view all the answers

When is an activity stopped?

When the user performs an action that starts another activity in the application. Signup and view all the answers

What should you do when an activity is paused?

Stop animations and release resources. Signup and view all the answers

Why should you not explicitly finish an activity?

Because the Android system manages the life of an activity. Signup and view all the answers

What happens when you rotate the device?

The app's activities are paused. Signup and view all the answers

What should you do in the onStop method?

Release all resources and save information. Signup and view all the answers

What is the purpose of the onPause method?

To stop animations and release resources. Signup and view all the answers

What is the primary purpose of a Content Provider in an Android app?

To share data between applications Signup and view all the answers

What happens when an Activity uses too many resources in an Android app?

It is destroyed to free up resources Signup and view all the answers

What is the primary purpose of an Intent in an Android app?

To pass information between applications Signup and view all the answers

What is the relationship between an Activity and its user interface in an Android app?

An Activity is a single screen with a user interface Signup and view all the answers

What is the primary purpose of a Broadcast Receiver in an Android app?

To respond to system-wide announcements Signup and view all the answers

What is the primary purpose of a Service in an Android app?

To perform long-running operations in the background Signup and view all the answers

What is the order of Activities in the Activity Stack in an Android app?

Most recently created is at the top Signup and view all the answers

What happens when the user presses the Back button or destroys an Activity in an Android app?

The previous Activity is brought to the top of the Activity Stack Signup and view all the answers

What happens when an activity is stopped?

The activity saves its progress and releases its resources Signup and view all the answers

What happens to the state of an activity when it is paused or stopped?

The state of the activity is retained. Signup and view all the answers

What is the purpose of the onPause method?

To release all resources and save progress Signup and view all the answers

What is the purpose of the onSaveInstanceState method?

To save the state of the activity and recreate it later. Signup and view all the answers

What happens to the activity when it is destroyed under normal circumstances?

The activity is finished and the state is destroyed. Signup and view all the answers

What happens when the user rotates their device?

The activity is stopped and then recreated Signup and view all the answers

What is the purpose of the Bundle in onSaveInstanceState?

To store the state of the activity and recreate it later. Signup and view all the answers

When is the onStop method called?

All of the above Signup and view all the answers

Why should you not explicitly finish an activity?

Because it is not recommended by the Android system Signup and view all the answers

What is the method used to restore the state of an activity when it is recreated?

onRestoreInstanceState Signup and view all the answers

What should you do when an activity is paused?

Stop animations and release resources Signup and view all the answers

What happens to the onPauseCounter when the app is rotated?

It is reset to 0. Signup and view all the answers

What is the purpose of the finish() method?

To destroy the activity and release resources. Signup and view all the answers

What happens when an activity is recreated after being stopped?

It resumes from the last saved state Signup and view all the answers

What is the purpose of the onStop method?

To release resources and save progress Signup and view all the answers

What is the relationship between the onSaveInstanceState and onRestoreInstanceState methods?

They are used together to save and restore the state. Signup and view all the answers

What is the primary difference between the Android application lifecycle and a typical Java application?

Android applications don't start with a call to main(String[]) Signup and view all the answers

What is the purpose of overloading callback methods in an Android application?

To ensure the application behaves well in different scenarios Signup and view all the answers

What happens if an Android application consumes valuable system resources when the user is not actively using it?

The application will be terminated by the system Signup and view all the answers

What is the purpose of the callback methods in the Android application lifecycle?

To correspond to specific stages of the Activity/application lifecycle Signup and view all the answers

What is the consequence of not overloading callback methods in an Android application?

The application will crash or lose the user's progress Signup and view all the answers

What is the primary purpose of the Activity lifecycle in an Android application?

To ensure the application behaves well in different scenarios Signup and view all the answers

What is the relationship between the Activity lifecycle and the Android OS?

The Activity lifecycle is controlled by the Android OS Signup and view all the answers

What is the primary purpose of the callback methods in an Android application?

To tear down the application Signup and view all the answers

What is the purpose of calling startActivityForResult()?

To start an activity and get some data Signup and view all the answers

What happens if an app is destroyed while a MediaPlayer is playing?

The MediaPlayer continues playing Signup and view all the answers

What is the purpose of overriding the onRestoreInstanceState method?

To restore the state of an activity Signup and view all the answers

What is the purpose of calling setResult() and finish()?

To add data to an intent and finish an activity Signup and view all the answers

What is the purpose of adding a new Activity to the Manifest?

To declare a new activity in the Android system Signup and view all the answers

What is the purpose of the onSaveInstanceState method?

To save the state of an activity Signup and view all the answers

What happens to the state of an activity when it is paused or stopped?

The state is lost Signup and view all the answers

What is the purpose of the onActivityResult() method?

To handle the result of an activity Signup and view all the answers

Study Notes

ListView

A type of ordered collection of selectable choices
Key attributes in XML:
- android:clickable to enable/disable the list
- android:id for unique ID in Java code
- android:entries for setting options from an array in strings.xml

Static Lists

Content is fixed and known before the app runs
Declare list elements in the strings.xml resource file
Example: listing operating systems like Android, iPhone, and Max OS X

Dynamic Lists

Content is read or generated as the program runs
Comes from a data file, internet, or other sources
Must be set in Java code

List Adapters

Helps turn list data into list view items
Common adapters: ArrayAdapter, CursorAdapter
Syntax: ArrayAdapter name = new ArrayAdapter(activity, layout, array);

Handling List Events

Lists don't use a simple onClick event
Event listeners must be attached in Java code, not in XML
Use anonymous inner classes to attach event listeners
List views respond to the following events:
- setOnItemClickListener for when an item in the list has been clicked
- setOnItemLongClickListener for when an item in the list has been clicked and held
- setOnItemSelectedListener for when an item in the list has been selected

Anatomy of an Android App and the App Lifecycle

An Android app has four primary components: Activities, Services, Content Providers, and Broadcast Receivers, each with different purposes and lifecycles.

Application Components

Activity: a single screen with a user interface, app may have several activities, subclass of Activity.
Service: an application component that performs long-running operations in the background with no UI.
Content Provider: a bridge between applications to share data, e.g., device's contacts information.
Broadcast Receiver: a component that responds to system-wide announcements, e.g., battery low, screen off, date changed.

Activity Stack

The most recently created Activity is at the top of the stack.
When the user presses the Back or the Activity is destroyed, the previous Activity comes to the top.

Primary States of an Activity

Active: the Activity is in the foreground and the user can interact with it.
Paused: the Activity is partially obscured by another Activity and the user cannot interact with it.
Stopped: the Activity is completely hidden and not visible to the user, but the instance and variables are retained.
Dead: the Activity is terminated (or never started).

Intents

Used to pass information between applications.

AndroidManifest.xml

All Activities that are part of the application must be registered in the Manifest.
Specify the Activity to start with.

Purpose of Lifecycle Phases

Entire lifetime: onCreate / onDestroy (load UI, start/stop threads).
Visible lifetime: onStart / onStop (access/release resources that influence UI, write info to files if necessary).
Foreground lifetime: onResume / onPause (restore/save state, start/stop audio/video/animations).

Activity Lifecycle App

Overload methods from Activity: onCreate(), onStart(), onResume(), onPause(), onStop(), onRestart(), onDestroy().
Use the Log class to log activity methods: v, d, i, w, e (VERBOSE, DEBUG, INFO, WARN, ERROR).
Create a TAG to filter logs.

Pausing and Stopping

Pausing: onPause method, stop animations, release resources, stop audio/video.
Stopping: onStop method, release all resources, save information (persistence).

Saving State

Activities that are paused or stopped retain their state (instance vars).
onSaveInstanceState method: save information to a Bundle, which is given back when restarted.

Activity Destruction

App may be destroyed under normal circumstances (finish or back button).
onSaveInstanceState method called to save state.
System calls onRestoreInstanceState method to recreate the Activity.

Starting Your Own Activities

Start a new Activity to accomplish a task or get some data.
Use an Intent, startActivityForResult, and onActivityResult to get a result.

Intent Demo

Intent holding a constant.
startActivityForResult and onActivityResult.
setResult and finish.

Application Components

An Android app consists of four primary components: Activity, Service, Content Provider, and Broadcast Receiver.
Each component has a different purpose and lifecycle.
An Activity is a single screen with a user interface, and an app can have multiple activities.
A Service is an application component that performs long-running operations in the background with no UI.
A Content Provider is a bridge between applications to share data.
A Broadcast Receiver is a component that responds to system-wide announcements.

Activity Stack

The Activity Stack is a Last-In-First-Out (LIFO) stack, where the most recently created activity is at the top.
When the user presses the Back button or the activity is destroyed, the previous activity is brought to the top.
If an activity uses too many resources, the system may destroy it to free up resources.

Activity Lifecycle

An Android app does not start with a call to main(String[]), but instead uses a series of callback methods invoked by the Android OS.
Each callback method corresponds to a specific stage of the activity/application lifecycle.
The callback methods are also used to tear down the activity/application.
Overloading callback methods is necessary to ensure the app behaves well:
- Does not crash when the user receives a phone call or switches to another app.
- Does not consume valuable system resources when the user is not actively using it.
- Does not lose the user's progress if they leave the app and return to it at a later time.
- Does not crash or lose the user's progress when the screen rotates between landscape and portrait orientation.

Activity Lifecycle Methods

onCreate: Called when the activity is created.
onPause: Called when the activity is paused, and the user should release resources and save information.
onStop: Called when the activity is stopped, and the user should release all resources and save information.
onSaveInstanceState: Called when the activity is destroyed, and the user should save information to a Bundle.
onRestoreInstanceState: Called when the activity is recreated, and the user should restore state data from the Bundle.

Saving and Restoring State

When an activity is paused or stopped, the state of the activity (instance variables) is retained.
When an activity is destroyed, the Activity object is destroyed, and the state is lost.
onSaveInstanceState can be used to save information to a Bundle, which is given back when the activity is restarted.
onRestoreInstanceState can be used to restore state data from the Bundle.

Starting Your Own Activities

You can start new activities within your activity to accomplish a task or get some data.
You can use startActivityForResult to start an activity and receive a result.
You need to add the new activity to the Manifest and override onActivityResult.

Intents

Intents are used to pass information between applications.
You can use startActivity to start an activity and pass data to it.
You can use startActivityForResult to start an activity and receive a result.

Playing Well (or not) With Others

The Play Sound button can cause a MediaPlayer to be created and play a sound.
If the app is destroyed, the MediaPlayer keeps playing, which is a bad practice.
You should clean up after yourself when your app is destroyed.

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Description

Learn about the key attributes of ListView in Android XML, including clickable, id, and entries.