Broadcast Receivers in Android Development
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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.

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    App Not Running

    When an app is not actively running in the background.

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    Context-registered Receiver

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

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    Starting an App from a Broadcast

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

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    Broadcasts

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

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    System

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

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    Receiving Broadcasts: Two Methods

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

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    Registering a BroadcastReceiver

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

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    Unregistering a BroadcastReceiver

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

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    onCreate()

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

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    onDestroy()

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

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    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.

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    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.

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    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.

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    Intent (in Android)

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

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    Unordered broadcast

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

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    Receivers (in Android)

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

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    App-to-App Broadcast

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

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    System-Initiated Broadcast

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

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    App Activation from Broadcast

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

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    Keeping Broadcast Active

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

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    Broadcast Response Time Limit

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

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    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.

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    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

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    Related Documents

    Chapter 4: Message Broadcasting (PDF)

    Description

    Test your knowledge on broadcast receivers in Android applications with this quiz. Explore the differences between context-registered and manifest-declared receivers, and understand their lifecycle implications. Gain insights into how to effectively register and unregister receivers to ensure optimal app performance.

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