KeyboardObserve Util for Android

KeyboardObserver.java

public class KeyboardObserver implements ViewTreeObserver.OnGlobalLayoutListener {
    private final static int MAGIC_NUMBER = 200;

    private SoftKeyboardToggleListener mCallback;
    private View mRootView;
    private float mScreenDensity = 1;
    private static HashMap<SoftKeyboardToggleListener, KeyboardObserver> sListenerMap = new HashMap<>();

    public interface SoftKeyboardToggleListener {
        void onToggleSoftKeyboard(boolean isVisible);
    }


    @Override
    public void onGlobalLayout() {
        Rect r = new Rect();
        mRootView.getWindowVisibleDisplayFrame(r);

        int heightDiff = mRootView.getRootView().getHeight() - (r.bottom - r.top);
        float dp = heightDiff / mScreenDensity;

        if (mCallback != null)
            mCallback.onToggleSoftKeyboard(dp > MAGIC_NUMBER);
    }


    public static void addKeyboardToggleListener(Activity act, SoftKeyboardToggleListener listener) {
        removeKeyboardToggleListener(listener);

        sListenerMap.put(listener, new KeyboardObserver(act, listener));
    }

    public static void removeKeyboardToggleListener(SoftKeyboardToggleListener listener) {
        if (sListenerMap.containsKey(listener)) {
            KeyboardObserver k = sListenerMap.get(listener);
            k.removeListener();

            sListenerMap.remove(listener);
        }
    }

    public static boolean isRegistered(SoftKeyboardToggleListener listener) {
        return sListenerMap.containsKey(listener);
    }

    public static void removeAllKeyboardToggleListeners() {
        for (SoftKeyboardToggleListener l : sListenerMap.keySet())
            sListenerMap.get(l).removeListener();

        sListenerMap.clear();
    }


    private void removeListener() {
        mCallback = null;

        mRootView.getViewTreeObserver().removeOnGlobalLayoutListener(this);
    }

    private KeyboardObserver(Activity act, SoftKeyboardToggleListener listener) {
        mCallback = listener;

        mRootView = ((ViewGroup) act.findViewById(android.R.id.content)).getChildAt(0);
        mRootView.getViewTreeObserver().addOnGlobalLayoutListener(this);

        mScreenDensity = act.getResources().getDisplayMetrics().density;
    }

}