how to update data of controls in viewml??

I want to change the data of a control named HTMLTextInput.
When I used HTMLInput::setValue() to change the data , the change was not displayed on screen.

I find out that HTMLTextInput::slotTextChanged can be "QT_connected" to QEditLine to update the data. but this function is protected and I can not use it by calling it directly. How to update the changed data? Is there any offical ways to update data in HTML controls? Or I have to do something shit  :-(