How to remove all callbacks from a Handler?

Optimal time to remove callbacks

Correct callback management is key to minimizing resource wastage in various situations:

• In the onStop() event: Invoke removeCallbacksAndMessages(null) inside onStop() of your Activity or Fragment.
• After finish(): Ensure you clear callbacks following a call to Activity.finish() to prevent executing code within a non-existing context.
• Preventing memory leaks: Avoid memory leaks within Android apps, particularly when your anonymous Runnables or Messages are holding a reference to your Activity.

@Override
protected void onStop() {
    super.onStop();
    handler.removeCallbacksAndMessages(null); // Just like a cleanup crew
}


Selective removal with Runnables

In some cases, you might need to clear specific callbacks instead of all. To achieve this, maintain persistent references to your Runnable instances:

Runnable myRunnable = new Runnable() {
    @Override
    public void run() {
        // Let's rock and roll
    }
};

handler.postDelayed(myRunnable, 1000); // Sets the timer

// Changes mind later to remove a specific callback
handler.removeCallbacks(myRunnable);


Preserving a ref to Runnables via global variables or a dedicated data structure offers a one-up on precise control and callback removal.

Advanced callback management

Global Handlers and Runnables

Establish global references for robust callback lifecycle management:

private Handler myGlobalHandler;
private Runnable myGlobalRunnable;


Initialize these in onCreate(), ensuring their survival across configuration changes and their accessibility for registration and deregistration of callbacks.

Main Looper utilization

When interacting with the main thread, utilize the main Looper:

Handler uiHandler = new Handler(Looper.getMainLooper());


This assures that the Runnable is executed on the main UI thread, preventing any thread-safety issues.

Logic-based callback management

Implement logic to decide when to post or remove Runnables:

if (shouldPostRunnable) {
    handler.post(myRunnable);
} else {
    handler.removeCallbacks(myRunnable);
}


This provides a firm hand on your callback flow, adjusting to user actions or state changes within your app.

Enhancements and alternatives

Customized Handler subclass

For encapsulating better Runnables and Messages management, implement a custom Handler subclass:

public class CustomHandler extends Handler {
    // Provides better management for all those pesky callbacks
}


This can be utilized to handle specific types of Messages or Runnables with shared behavior or requirement.

Advanced message-passing mechanisms

For advanced inter-component app communications, consider alternatives such as EventBus or LiveData. They provide a more structured event passing methodology than independent Handlers and Runnables.

Precise management for Runnables

Implement wrappers for your Runnables equipped with timestamp or priority for more effective scheduling and removal. Let's say you maintain them in PriorityQueue or a HashMap with timestamps, now you can efficiently perform removals or adjustments based on time or priority.