Question

I have a requirement where i need to allow only numbers in text box. if user tries to enter any other character other than numbers then we need to cancel the event. Please help me how to achieve this?

Thanks!

Answer 1

You just have to validate the users input on a certain event. It can be e.g. on every keystroke (KeyPressEvent), when the TextBox loses focus (ValueChangeEvent), on a button press (ClickEvent), and so on. You implement an event handler, e.g. KeyPressHandler and register your implementation with the TextBox. Then in your handler you validate the TextBox value and if it contains something else than numbers, you just return from the method, probably somehow telling the user that the value was invalid.

Something like this:

final TextBox textBox = new TextBox();
textBox.addKeyPressHandler(new KeyPressHandler() {
    @Override
    public void onKeyPress(KeyPressEvent event) {
        String input = textBox.getText();
        if (!input.matches("[0-9]*")) {
            // show some error
            return;
        }
        // do your thang
    }
});

If you have a lot of validation to do, you probably want to introduce some validation framework which saves you from a lot of reinventing the wheel. There may be better alternatives nowadays but personally I have been quite satisfied with the GWT-VL validation framwork.