# How to create a lifecycle aware custom class in Android.

We all know, each component in Android has its lifecycle, be it Activity, Fragment or Service. Each component gets created and destroys (and a few other stages in between).

To create a custom class that is lifecycle aware inherently, we can use a set of libraries provided under [jetpack lifecycle](https://developer.android.com/jetpack/androidx/releases/lifecycle).

For example, I want to create a timer, which invokes a method on each interval, and also, it should be lifecycle aware so it dies with its owner.

Firstly, we will create an interface that extends `LifecycleOwner`, this interface is implemented all new `androidx.` components.

```java
public interface OnIntervalListener extends LifecycleOwner {
    void onTimerInterval();
}
```

Now, we create out actual timer,

```java
/**
 * @implNote An implementation of lifecycle aware timer, can be attached to Activity or fragment
 */
public class LifecycleAwareTimer implements Runnable, DefaultLifecycleObserver {

    public interface OnIntervalListener extends LifecycleOwner {
        void onTimerInterval();
    }

    private final Handler mHandler = new Handler(Looper.getMainLooper());

    private final long mInterval;

    private final OnIntervalListener mOnIntervalListener;

    public LifecycleAwareTimer(long interval, @NonNull OnIntervalListener onIntervalListener) {
        mInterval = interval;
        mOnIntervalListener = onIntervalListener;

        mOnIntervalListener.getLifecycle().addObserver(this);
    }

    @Override
    public void run() {
        mOnIntervalListener.onTimerInterval();
    }

    @Override
    public void onResume(@NonNull LifecycleOwner owner) {
        mHandler.removeCallbacksAndMessages(null);
        mHandler.postDelayed(this, mInterval);
    }

    @Override
    public void onPause(@NonNull LifecycleOwner owner) {
        mHandler.removeCallbacksAndMessages(null);
    }

    @Override
    public void onDestroy(@NonNull LifecycleOwner owner) {
        mHandler.removeCallbacksAndMessages(null);
        mOnIntervalListener.getLifecycle().removeObserver(this);
    }
}
```

Now, you can use it creates a new instance from Activity or Fragment and it will die once its owner dies.