Question

I want to implement a button that counts down when pressed. The idea is to allow the user to cancel the activation of the button. Once pressed, I would like for the button to change to red and read “CANCEL (3)” and countdown to “CANCEL (0)” and if it is pressed again, the countdown will stop and nothing will happen. If it is not canceled, the app will go to the next screen after time expires. Is there a way to update a button’s text each second (for the countdown) and change its functionality?

Thanks

Answer 1

You can use postDelayed on a Handler to invoke your method later on the UI thread so that you can update the UI.

There’s actually a very nice article about how this is done on Android already: http://developer.android.com/resources/articles/timed-ui-updates.html

You can get a Handler either by creating one in code running on the UI thread, or by calling getHandler() on a view (e.g. your button itself).

I’d provide an example, but the article linked already does so with great detail and clarity, so I’ll defer to it.

Edit: here’s a rough overview of how this will look. I don’t have the Android SDK installed right now, so I can’t verify that this works.

public class CountdownButton extends Button {
  private boolean isCounting = false;
  private int count;

  private final Runnable countdownRunnable = new Runnable() {
    @Override
    public void run() {
      setText(Integer.toString(count));
      if (count > 0) {
        count--;
        getHandler().postDelayed(countdownRunnable, 1000);
      } else {
        // count reached zero
        isCounting = false;
        setText("boom");
      }
    }
  }

  private final View.OnClickListener onClickListener = new View.OnClickListener() {
    @Override
    public void onClick(View view) {
      if (isCounting) {
        // stop counting
        isCounting = false;
        getHandler().removeCallbacks(countdownRunnable);
        setText("cancelled");
      } else {
        // start counting
        isCounting = true;
        count = 10;
        countdownRunnable.run();
      }
    }
  }

  public CountdownButton(Context context) {
    super(context);
    setOnClickListener(onClickListener);
  }

  public CountdownButton(Context context, AttributeSet attrs) {
    super(context, attrs);
    setOnClickListener(onClickListener);
  }

  public CountdownButton(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
    setOnClickListener(onClickListener);
  }
}

The timing may not be perfect (especially if there’s a lot of other CPU work going on), but it should be good enough for your purposes.