Android : Need help get content view height - Android

I need some help to get my custom webView CONTENT height, please check below is my code

    webView.setOnTouchListener(new View.OnTouchListener() {
        @Override
        public boolean onTouch(View v, MotionEvent event) {

            final int displayHeight = webView.getHeight();
            final int contentRange = webView.getContentHeight();
            final int y = v.getScrollY();


            switch (event.getAction()) {
                case MotionEvent.ACTION_DOWN:

                    Log.d("Get webView height ", "" + displayHeight); // Result : 528
                    Log.d("Get webView content height ", "" + contentRange); // Result : 2112
                    Log.d("Get webView content scroll top ", "" + y);

                    return false;

                case MotionEvent.ACTION_CANCEL:
                case MotionEvent.ACTION_UP:
                case MotionEvent.ACTION_MOVE:

            }

            return false;
        };

Above is my code to get my custom webView content height with webview.setOnTouchListener, that code is work.

But, now I want to get my custom WebView content height from button click, that does not work, what I got is always get a height of my webView not the content height, below my code for button click

Button btn = (Button) this.getActivity().findViewById(R.id.btnCLick);

    btn.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {

            int webViewContentHeight = webView.getContentHeight();

            Log.d("Get my custom webView content height", " " + webViewContentHeight); // Result : 528

        }
    });

Much appreciate if I can have a detailed procedure, thanks.