How to Prevent Accidental App Exit w/in Android Fragments/Activities?

Question

How Do I Prevent Accidental App Exit w/in Android?

IE: When the he/she presses the back button and reaches the last activity in the BackStack, show a toast to ask if the user wants to exit using the onBackPressed() method.

Also, It needs to function with backStacks for fragments.

Answer 1

This functionality can easily be implemented by overriding main activity's onBackPressed() method. In this example when user presses back button then the app will display a toast for 4 seconds on which time a new back press terminates the app immediately.

ref

You can put it in a BaseActivity that extends Activity like this:

public class BaseActivity extends Activity{

    private Toast toast;
    private long lastBackPressTime = 0;
    . . .

    /**
     * Prevent accidental app exit by requiring users to press back twice when
     * the app is exiting w/in 4sec
     */
    @Override
    public void onBackPressed() {
      if (this.lastBackPressTime < System.currentTimeMillis() - 4000) {
        toast = Toast.makeText(this, "Press back again to close this app", 4000);
        toast.show();
        this.lastBackPressTime = System.currentTimeMillis();
      } else {
        if (toast != null) {
        toast.cancel();
      }
      super.onBackPressed();
     }
    }
    . . . 
}

EDIT: ADDED FRAGMENT BACKSTACK COMPATABILITY

For use to detect the last fragment in a bacstack whos application is solely using fragments, I strongly suggest putting your dispatchKeyEvents in a BaseActivity class and implementing the above method like so:

public class BaseActivity extends Activity {

    public boolean dispatchKeyEvent(KeyEvent event) {
        int backCount = getFragmentManager().getBackStackEntryCount();
        int action = event.getAction();
        int keyCode = event.getKeyCode();

        FragmentManager fm = getFragmentManager();

    . . .

        case KeyEvent.KEYCODE_BACK :
                if (action == KeyEvent.ACTION_DOWN && backCount == 0) {
                    onexitNotify();
                }else {
                    fm.popBackStack();
                }
                return true;

            default :
                return super.dispatchKeyEvent(event);
        }
    }

/**
 * Prevent accidental app exit by requiring users to press back twice when
 * the app is exiting w/in 8sec
 */
    private Toast toast;
    private long lastBackPressTime = 0;

    public void onexitNotify() {
        if (this.lastBackPressTime < System.currentTimeMillis() - 8000) {
            toast = Toast.makeText(this, "Press back again to close this app", 8000);
            toast.show();
            this.lastBackPressTime = System.currentTimeMillis();
        } else {
            if (toast != null) {
                toast.cancel();
            }
            super.onBackPressed();
        }
    }
}

*If you're using 2.0+, onBackPressed() simplifies the amount of code needed so onKeyDown() is not needed.

Per androd patterns recomendation:

Some applications prompt user when it is about to exit. This seems to be particularly common with game apps. This practice is not recommended in normal applications. A confirmation prompt would disrupt user's normal workflow. Even in games using this option should be very carefully considered.

Answer 2

You can check when the back key is pressed in the main activity of your app. You can then show user an alertdialog for a confirmation to exit.

public boolean onKeyDown(int keyCode, KeyEvent event) {
    //Handle the back button
    if(keyCode == KeyEvent.KEYCODE_BACK) {          
        checkExit();             
        return true;
    }       
    else {
        return super.onKeyDown(keyCode, event);
    }

}

private void checkExit()
{
    AlertDialog.Builder builder = new AlertDialog.Builder(this);        
    builder.setMessage("Are you sure you want to exit?")
           .setCancelable(false)
           .setPositiveButton("Yes", new DialogInterface.OnClickListener() {
               public void onClick(DialogInterface dialog, int id) {

                   //take actions here accordingly as the user has pressed yes
               }
           })
           .setNegativeButton("No", new DialogInterface.OnClickListener() {
               public void onClick(DialogInterface dialog, int id) {
                    dialog.cancel();
               }
           });      
    AlertDialog alert = builder.create();
    alert.show();       
}