Broadcast Receivers in Android Development

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to Lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is one method of receiving broadcasts in an app?

  • Web page listeners
  • Socket connections
  • Manifest-declared receivers (correct)
  • HTTP callbacks

Which option describes a method that does not work for declaring a receiver?

  • Through context registration
  • By adding to the manifest (correct)
  • Using external libraries
  • None of the above

What are context-registered receivers primarily used for?

  • To receive system-wide announcements
  • To listen for network changes
  • For user interface updates
  • For app-specific broadcast handling (correct)

Why might an app developer choose context-registered receivers over manifest-declared receivers?

<p>Dynamic registration tailored to app state (D)</p> Signup and view all the answers

Which method of receiving broadcasts is not mentioned?

<p>Remote service listeners (B)</p> Signup and view all the answers

When is the appropriate time to unregister a receiver that was registered in onCreate(Bundle)?

<p>In onDestroy() of the activity (A)</p> Signup and view all the answers

What could happen if a receiver is not unregistered correctly?

<p>It may cause memory leaks (D)</p> Signup and view all the answers

What context should be used for registering a receiver in onCreate(Bundle)?

<p>Activity context (D)</p> Signup and view all the answers

What is the potential risk of registering a receiver outside of the appropriate lifecycle methods?

<p>The receiver may leak memory or resources (A)</p> Signup and view all the answers

Why should you be careful where you register a receiver?

<p>To manage its lifecycle and prevent resource leaks (C)</p> Signup and view all the answers

What role does the receiver play in an app's operation?

<p>It serves as a separate entry point into the app. (A)</p> Signup and view all the answers

What is a key characteristic of the receiver in relation to the app's state?

<p>It allows the app to respond to broadcasts regardless of its running state. (B)</p> Signup and view all the answers

What happens if an app is not currently running when a broadcast is sent?

<p>The app automatically restarts to handle the broadcast. (C)</p> Signup and view all the answers

Which statement best describes the interaction between the receiver and the app lifecycle?

<p>The receiver acts as a trigger for the app regardless of its lifecycle status. (C)</p> Signup and view all the answers

In which scenario can the receiver be particularly useful?

<p>When the app needs to perform tasks in the background. (D)</p> Signup and view all the answers

What method is used to send broadcasts to one receiver at a time in Android?

<p>sendOrderedBroadcast(Intent, String) (C)</p> Signup and view all the answers

Which of the following describes the function of the sendOrderedBroadcast method in Android?

<p>Allows receivers to process the broadcast in a specific order. (C)</p> Signup and view all the answers

In what scenario would you typically use the sendOrderedBroadcast method?

<p>When the order of processing by receivers is essential. (D)</p> Signup and view all the answers

Which of the following is not a way for Android apps to send broadcasts?

<p>sendSequentialBroadcast(Intent, String) (C)</p> Signup and view all the answers

What is a key characteristic of sending broadcasts in Android?

<p>Broadcasts can be delivered to receivers in a specified order. (B)</p> Signup and view all the answers

What is a major limitation of the more efficient broadcasting method described?

<p>Receivers cannot read results from other receivers. (D)</p> Signup and view all the answers

Which of the following is NOT a consequence of the more efficient broadcasting method?

<p>Receiving nodes can abort the broadcast. (C)</p> Signup and view all the answers

How does the more efficient broadcasting method affect data handling by receivers?

<p>Receivers do not propagate data received from broadcasts. (C)</p> Signup and view all the answers

What capability is lost due to the more efficient broadcasting method?

<p>The ability for receivers to abort the operation. (B)</p> Signup and view all the answers

Which statement best reflects the trade-offs of the efficient broadcasting method?

<p>Reduced latency at the cost of data accessibility. (C)</p> Signup and view all the answers

What is a key expectation of the system when using onReceive() for broadcasting?

<p>The broadcast should be completed quickly, ideally within a specific time. (D)</p> Signup and view all the answers

What happens if the expected time frame for a broadcast is exceeded?

<p>The broadcast may be terminated ungracefully. (C)</p> Signup and view all the answers

Which of the following describes a consequence of keeping the broadcast active too long?

<p>Potential failure of the broadcast to relay its message. (B)</p> Signup and view all the answers

Why is it important to finish with the broadcast quickly?

<p>To minimize resource consumption. (D)</p> Signup and view all the answers

What is a recommended practice for handling broadcasts in relation to onReceive() functionality?

<p>Complete the task within 10 seconds to comply with system expectations. (A)</p> Signup and view all the answers

Flashcards

Entry Point

A separate point where a user can start using an app.

Broadcast Receiver

A component of an app that listens for and responds to system-wide events.

Manifest-declared Receiver

An app component that can be declared in the AndroidManifest.xml file to listen for specific broadcasts.

Broadcast

A message sent from one part of your app to another part of your app.

Signup and view all the flashcards

App Not Running

When an app is not actively running in the background.

Signup and view all the flashcards

Context-registered Receiver

A way to register a receiver dynamically at runtime, using a Context object.

Signup and view all the flashcards

Starting an App from a Broadcast

The ability for an app to start and deliver messages even if it's not currently running.

Signup and view all the flashcards

Broadcasts

System-wide events that can be received by apps, often triggered by the system itself.

Signup and view all the flashcards

System

A system that can initiate actions, such as sending broadcasts, without being explicitly programmed by the user.

Signup and view all the flashcards

Receiving Broadcasts: Two Methods

Two different approaches that apps can use for receiving broadcasts: manifest-declared receivers and context-registered receivers.

Signup and view all the flashcards

Registering a BroadcastReceiver

The process of creating a connection between a component (like an Activity) and a BroadcastReceiver to receive broadcast messages.

Signup and view all the flashcards

Unregistering a BroadcastReceiver

The process of removing the connection between a component and a BroadcastReceiver.

Signup and view all the flashcards

onCreate()

The lifecycle method of an Activity that is called when the Activity is created.

Signup and view all the flashcards

onDestroy()

The lifecycle method of an Activity that is called when the Activity is destroyed.

Signup and view all the flashcards

Leaking a Receiver

The process of keeping a reference to an object, preventing it from being garbage collected, even when it's no longer needed.

Signup and view all the flashcards

sendOrderedBroadcast(Intent, String)

A method in the Android operating system that sends a broadcast to one app at a time, allowing for ordered processing and potential modification of the broadcast.

Signup and view all the flashcards

Broadcasts (in Android)

A powerful mechanism in Android that allows apps to communicate with each other without direct interaction, notifying them of certain events or changes.

Signup and view all the flashcards

Intent (in Android)

A structured object used within Android to encapsulate data and actions, carrying information about the broadcast.

Signup and view all the flashcards

Unordered broadcast

A type of broadcast that sends a message to all interested apps simultaneously.

Signup and view all the flashcards

Receivers (in Android)

A component of Android applications that listen for and respond to broadcasts.

Signup and view all the flashcards

App-to-App Broadcast

A message sent from one part of your app to another part of your app.

Signup and view all the flashcards

System-Initiated Broadcast

The system can trigger events that apps can listen to and respond to, like notifications or battery changes.

Signup and view all the flashcards

App Activation from Broadcast

Apps can start and receive messages even when not running, making them more responsive and proactive.

Signup and view all the flashcards

Keeping Broadcast Active

A technique that keeps an app's broadcast receiver active even after handling a received message.

Signup and view all the flashcards

Broadcast Response Time Limit

The system's expectation to receive quick responses from broadcast receivers, typically within 10 seconds.

Signup and view all the flashcards

Receiving Broadcasts While App Is Not Running

The ability of a broadcast receiver to respond to system events even when the app is not actively running, allowing the app to start and handle messages.

Signup and view all the flashcards

Study Notes

Android Broadcasts Overview

  • Android apps can send or receive broadcast messages from the Android system and other apps.
  • This is similar to a publish-subscribe design pattern.
  • Broadcasts are sent when interesting events occur.
  • System events include system boot, device charging, or new data downloads.
  • Apps can also send custom broadcasts to notify other apps.

Broadcast Delivery Optimization

  • The Android system optimizes broadcast delivery for optimal system health.
  • Therefore, broadcast delivery times are not guaranteed.
  • Apps needing low-latency interprocess communication should use bound services.

Receiving Specific Broadcasts

  • Apps can register to receive specific broadcasts.
  • When a broadcast is sent, the system automatically routes it to subscribed apps.

Broadcasts as Messaging System

  • Generally, broadcasts can act as a messaging system between apps.
  • They can occur outside the normal user flow.
  • Be careful not to overuse broadcasts to avoid slow system performance.

System Broadcasts

  • The system automatically sends broadcasts for various system events.
  • Airplane mode toggling is an example.
  • System broadcasts target all subscribed apps.

Intent object

  • Broadcast messages are wrapped in Intent objects.
  • Action string in Intent object identifies the event, e.g., android.intent.action.AIRPLANE_MODE.
  • Extra fields can carry extra information (e.g., Airplane Mode status).

Complete List of System Broadcast Actions

  • For a full list, consult the BROADCAST_ACTIONS.TXT file within the Android SDK.
  • Each broadcast action has a corresponding constant field.
  • Documentation on each broadcast action is available in the constant field.

Changes in System Broadcast Behavior

  • Android continuously updates how system broadcasts behave.
  • Android 14 optimizes broadcast delivery in the cached state.
  • Less important broadcasts (e.g., ACTION_SCREEN_ON) are deferred while the app is in a cached state.
  • Important system broadcasts remove apps from the cached state to ensure delivery.
  • Android Version 9 (API level 28) broadcasts don't include user location or personal data.
  • System broadcasts from Wi-Fi don't provide SSIDs, BSSIDs, connection information, or scan results in Android 9 or higher.
  • Use getConnectionInfo() to retrieve this information.

Android 8.0 Broadcast Restrictions

  • The system imposes additional restrictions on manifest-declared receivers in Android 8.0 (API level 26).
  • Apps targeting Android 8.0 or higher cannot use manifest to declare receivers for most implicit broadcasts.
  • Context-registered receivers can be used when a user is actively using the app.

Android 7.0 Broadcast Removal

  • Android 7.0 (API level 24) and higher don't send ACTION_NEW_PICTURE, ACTION_NEW_VIDEO system broadcasts.
  • Use registerReceiver(BroadcastReceiver, IntentFilter) to register connectivity broadcasts.

Receiving Broadcasts: Manifest-Declared Receivers

  • If a broadcast receiver is declared in the app manifest, the system launches the app if it is not already running.

Receiving Broadcasts: Specific Steps

  • In the manifest, specify the <receiver> element.
  • Intent filters specify the broadcast actions the receiver subscribes to.

Receiving Broadcasts: Subclass BroadcastReceiver

  • Subclass BroadcastReceiver and implement the onReceive method to process broadcast information.

Receiving Broadcasts: Context-Registered Receivers

  • Context-registered receivers receive broadcasts as long as their registering context is valid.
  • App running = Context-level receiver.
  • Activity running = Activity-level receiver.

Context-Registered Receiver Steps

  • In your app, create a BroadcastReceiver instance, an IntentFilter instance that targets specific broadcasts, and a Context.
  • Register the receiver using the registerReceiver() method.
  • Unregister the receiver using the unregisterReceiver() method when not needed. (Note context used for registering)

Effects On Android Processes: Receivers

  • The system manages a BroadcastReceiver's process based on its activity.
  • A foreground process can run the receiver's onReceive() method.
  • The system can terminate a process (especially for infrequent apps), that only has manifest declared receivers to free up memory

Effects on Process State: Broadcast Receivers

  • Broadcast receivers should avoid long-running background threads.
  • When onReceive() finishes, the system may resume the process .
  • Using JobScheduler to keep processes alive is often recommended to prevent abrupt process termination .

Sending Broadcasts

  • Android offers sendOrderedBroadcast(), which sends broadcasts to receivers one at a time, and sendBroadcast(), which sends to all receivers in undefined order.
  • Prioritized receivers (android:priority) determine running order.

Sending Broadcasts (Code Example)

  • Intent object for broadcast message includes the sender's package and action information.

Restricting Broadcasts with Permissions

  • Permissions restrict broadcast access to specific apps.
  • Specify permissions in the sendBroadcast() or sendOrderedBroadcast() calls.
  • If android:exported is set to false in the manifest, the receiver does not process broadcasts from sources outside the app.

Security Considerations

  • Avoid information disclosure in broadcasts via implicit intents.
  • Specifying permissions protects sensitive data.
  • Choosing the right broadcast delivery method avoids resource exhaustion or unwanted activity creation

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Quiz Team

Related Documents

Chapter 4: Message Broadcasting (PDF)

More Like This

Use Quizgecko on...
Browser
Open
Browser
Browser