Oddly enough, REAL Studio 2010 through Release 3 does not offer an event meaning the user (or code) changed the value in a TextField. On every keystroke, both "KeyUp" and "TextChange" fire. But that is too often. In boring database-backed business apps, we usually don't care about the user's edit as it happens. We only care after the edit, when the change is complete.
Hopefully the REAL Software team will add such an event in the future. In the meantime, I am giving away a single file, a subclass of TextField named "TextField_ValueTracking". I have an example project to demonstrate how it works. See here.