How does Looper work internally in Android SDK?

The Looper in Android is a fundamental component that handles the message queue for a thread, allowing it to process messages and run tasks asynchronously. Internally, a Looper works by maintaining a queue where messages and runnables are added, enabling the thread to process them one at a time in a sequential order.

Every thread can have its own Looper, and the main thread in an Android application is always associated with a Looper. The message queue operates in a loop, where the Looper retrieves messages from the queue and dispatches them to their intended handlers.

How Looper Works Internally

  • Message Queue: The main component where messages and runnables are stored.
  • Thread Association: Each thread can be associated with a Looper, but it's typically used in the main thread.
  • Looping Mechanism: The Looper runs in a loop, continuously checking for new messages to process.
  • Handler: A Handler is used to send messages to the Looper’s message queue.

Example of Looper:

// Create a new thread with a Looper new Thread(new Runnable() { @Override public void run() { Looper.prepare(); // Prepares the Looper for the current thread Handler handler = new Handler(); // Create a new Handler associated with this thread's Looper // Post a Runnable to the message queue handler.post(new Runnable() { @Override public void run() { // Code to run in this thread } }); Looper.loop(); // Start the message queue loop } }).start();

Looper Android Message Queue Background Thread Asynchronous Processing Handler

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