Specify a validator on the text field that will check to see if there are spaces. If so, return false and it will mark the field as invalid. RegExp is the way I would check.
Specify a custom VType. This works very similar to validator.
Just specify the maskRe property on the text field to a valid RegExp.
If you specify the maskRe property it will do the check as you type so if the RegExp test returns false, it won't allow that key to be typed. If you create your own VType and give it a RegExp, it will put that RegExp onto the maskRe property and will stop the key from being put on the field but you can also have a function to do more testing and/or return an error string. These two do validations as you type, validator will happen when you do a test to see if the field/form is valid.