Android: Kotlin: custom webView - cannot be invoked as a function. The function 'invoke()' is not found

I has one activity (ContactActivity.kt) that contain only one webView component. Activity write on Kotlin.

I want to replace webView with my custom webView (ObservableWebView.java).

So here code (MyActivity.kt):

class ContactActivity : AppCompatActivity() {

        @SuppressLint("NewApi")
        override fun onCreate(savedInstanceState: Bundle?) {
            verticalLayout {
     val observableWebView = object : ObservableWebView(MainApp.getAppContext())
            observableWebView { // error here
                    setOnLongClickListener(object : View.OnLongClickListener {
                        override fun onLongClick(v: View): Boolean {
                            return true
                        }
                    })
                }
            }
       }
    }

Also I has custom webView - ObservableWebView.java:

public class ObservableWebView extends WebView {
    private OnScrollChangedCallback mOnScrollChangedCallback;

    public ObservableWebView(final Context context) {
        super(context);
    }

    public ObservableWebView(final Context context, final AttributeSet attrs) {
        super(context, attrs);
    }

    public ObservableWebView(final Context context, final AttributeSet attrs, final int defStyle) {
        super(context, attrs, defStyle);
    }

    @Override
    protected void onScrollChanged(final int l, final int t, final int oldl, final int oldt) {
        super.onScrollChanged(l, t, oldl, oldt);
        if (mOnScrollChangedCallback != null) mOnScrollChangedCallback.onScroll(l, t);
    }

    public OnScrollChangedCallback getOnScrollChangedCallback() {
        return mOnScrollChangedCallback;
    }

    public void setOnScrollChangedCallback(final OnScrollChangedCallback onScrollChangedCallback) {
        mOnScrollChangedCallback = onScrollChangedCallback;
    }

    /**
     * Impliment in the activity/fragment/view that you want to listen to the webview
     */
    public static interface OnScrollChangedCallback {
        public void onScroll(int l, int t);
    }
}

But I get compile error in MyActivity.kt:

Error:(145, 13) Expression 'observableWebView' of type '<no name provided>' cannot be invoked as a function. The function 'invoke()' is not found