Unless I missed them, I see no specific events to watch / handle for the FileUploadField component.
I see it has an internal onChange handler, but it doesn't fire an external event to be caught.
I would appreciate a SelectEvent or a ChangeEvent to be fired when the user selects a file.
It is useful eg. to validate a form only when a file is chosen. Currently, I have to check the length of the value of the field in the SelectEvent of the OK button, which isn't elegant. I want to deactivate the button and validate it only when all fields are valid, including the FileUploadField.
The fix for this bug has been included in the public release of Sencha GXT 3.0.0. You'll be able to observe this change in the GXT source. Although we're confident that this issue has been resolved, please reply here (or start a new bug thread linking to this one) if you continue to notice issues.