Observe Keyboard open or hidden

KeyboardObserver.java

public class KeyboardObserver implements ViewTreeObserver.OnGlobalLayoutListener {

    public interface Callback {
        void onKeyboardVisible();

        void onKeyboardHidden();
    }

    WeakReference<View> view;
    Callback callback;

    public KeyboardObserver(View view, Callback callback) {
        this.view = new WeakReference<>(view);
        this.callback = callback;
    }

    /**
     * subscribe to start observing keyboard changes
     */
    public void subscribe() {
        this.view.get().getViewTreeObserver().addOnGlobalLayoutListener(this);
    }

    /**
     * Unsubscribe to remove listener and avoid leaks
     */
    public void unsubscribe() {
        this.view.get().getViewTreeObserver().removeOnGlobalLayoutListener(this);
    }

    @Override
    public void onGlobalLayout() {
        Rect r = new Rect();
        view.get().getWindowVisibleDisplayFrame(r);
        int screenHeight = view.get().getRootView().getHeight();

        // r.bottom is the position above soft keypad or device button.
        // if keypad is shown, the r.bottom is smaller than that before.
        int keypadHeight = screenHeight - r.bottom;

        if (keypadHeight > screenHeight * 0.20) { // 0.20 ratio is perhaps enough to determine keypad height.
            // keyboard is opened
            if (callback != null) {
                callback.onKeyboardVisible();
            }
        } else {
            // keyboard is closed
            if (callback != null) {
                callback.onKeyboardHidden();
            }
        }
    }
}