You might be able to detect it with the ItemStateListener API, but it might not work on all phones...
Depending on what exactly you are wanting to detect, maybe you could have a seperate monitor
thread that checks textField.getString() every, say, 250 milliseconds to see if the TextField's
String has been shortened or cleared entirely. But having said that, I'm sure if this would work ok if the TextField maximises to full screen when it is being edited...
...but just some ideas anyway.