Clicking the back button twice to exit an activity

java

prompt-engineering

best-practices

synchronization

byAnton Shumikhin·Feb 2, 2025

Implement a boolean to track the back button press and use Handler for delay. Below is the essential code to require a double back press to exit an activity:

private boolean isBackPressedOnce = false;
private Handler backPressHandler = new Handler();
private final Runnable backPressRunnable = () -> isBackPressedOnce = false; // Who says we can't use lambdas to play tricks?

@Override
public void onBackPressed() {
    // Jedi trick: fool the system into believing that you're gone, unless...you want to be Gone for Real!
    if (isBackPressedOnce) {
        super.onBackPressed(); // Tricked ya!
        return;
    }
    this.isBackPressedOnce = true;
    // Hey user! React quickly!! Two seconds and I will selectively "forget" your wish to leave
    Toast.makeText(this, "Press BACK again to exit", Toast.LENGTH_SHORT).show(); 
    backPressHandler.postDelayed(backPressRunnable, 2000); // "Forgetfulness" ticking time bomb...
}

This code:

Initiates isBackPressedOnce variable which flag the first back press.
UtilizesonBackPressed() to customize back button behavior.
Displays a Toast to guide the user.
Resets isBackPressedOnce with Handler().postDelayed after 2 seconds, if no second press is detected within this period it's assumed that the user has rethought their action of leaving.

Acting smart: Delay & Lifecycle Management

A well-handled lifecycle makes your app resilient and friendly to poor user patterns like rapid fire button presses. Clean up our Handler and Runnable in onDestroy() to stay leak-free:

@Override
protected void onDestroy() {
    super.onDestroy();
    backPressHandler.removeCallbacks(backPressRunnable); // Clean up after play, like a good boy.
}

Excited user represents a challenge. Incase a user navigates back to the activity reset the isBackPressedOnce flag again in onResume():

@Override
protected void onResume() {
    super.onResume();
    isBackPressedOnce = false; // Back in the game! New beginnings...
}

Enhanced UX: Mastering OnKeyDown

When a user's focus is away from the main activity (maybe on another UI element, typical user, right?), you may notice that sometimes onBackPressed() won't get called on button pressses. Darn things! Control key events finer with onKeyDown:

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if (keyCode == KeyEvent.KEYCODE_BACK && event.getRepeatCount() == 0) {
        onBackPressed(); // Like a boss! Never miss a back press again.
        return true;
    }
    return super.onKeyDown(keyCode, event); // Nothing to see here, move along.
}

Define your own rules of the game in interaction scenarios, ensuring the back button press is handled seamlessly and consistently.

Everything you wanted to know about: Advanced implementations

Prevent double-toast on double press

private Toast backToast;

@Override
public void onBackPressed() {
    if (backToast != null) backToast.cancel();  // Remove previous toast, if it exists. One toast is enough for any breakfast... or code.
}

This counteracts cluttered toasts, cleans the display and maintains a streamlined UI.

Timing and you: Getting it just right

The importance of time in double press

Set a specific time interval that the user has to respond to the prompt by pressing back a second time. This reduces accidental exits and respects the user's learned UX patterns.

Playing nice with threads: Handle Simultaneity

private synchronized void resetBackPressStatus() {
    isBackPressedOnce = false;
}

private Runnable backPressRunnable = this::resetBackPressStatus; // Mr. Lambda saves the day.

With synchronization, avoid hilarious but potentially disastrous scenarios where multiple threads may try to access and modify the back press tracking variable causing an unintended exit! The horror!

Going beyond Toast: Adding more visual cues

Consider adding some layers above a basic Toast. Perhaps using subtle animations that reinforce the double-tap instruction, providing a more engaging and intuitive interface.

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