Keyboard visibility utils

KeyboardVisibilityUtils.java

import android.app.Activity;
import android.view.View;
import android.view.ViewTreeObserver;

public class KeyboardVisibilityUtils {
    private int appHeight;
    private final View contentView;
    private ViewTreeObserver.OnGlobalLayoutListener layoutListener;

    public KeyboardVisibilityUtils(Activity activity) {
        contentView = activity.findViewById(android.R.id.content);
    }

    public void subscribe(OnKeyboardVisibilityListener keyboardVisibilityListener) {
        layoutListener = new ViewTreeObserver.OnGlobalLayoutListener() {
            private int previousHeight;

            @Override
            public void onGlobalLayout() {
                int newHeight = contentView.getHeight();
                if (newHeight == previousHeight)
                    return;
                
                previousHeight = newHeight;

                if (newHeight >= appHeight) {
                    appHeight = newHeight;
                }
                
                if (newHeight != 0) {
                    if (appHeight > newHeight) {
                        keyboardVisibilityListener.onKeyboardVisibilityChanged(true);
                    } else {
                        keyboardVisibilityListener.onKeyboardVisibilityChanged(false);
                    }
                }
            }
        };
        contentView.getViewTreeObserver().addOnGlobalLayoutListener(layoutListener);
    }

    public interface OnKeyboardVisibilityListener {
        void onKeyboardVisibilityChanged(boolean keyboardVisible);
    }

    public void unsubscribe() {
        contentView.getViewTreeObserver().removeOnGlobalLayoutListener(layoutListener);
        layoutListener = null;
    }
}