Thank Alec for a simple way! 

But if use your solution, button "QT" will be always disabled, i don't know why!! 

Thank Scott!

Now i want to enable/disable button 'QT' if the value in TextField 'TF' is true/false after click on button 'EX'

Action[ACT](Evaluate('TF' = myLogicProc), SetOption('QT'(enabled) = myLogicProc))

But there's an error!

Error, (in Maplets:-Tools:-CleanUp:-SetOption) the option value `myLogicProc` is not of type `truefalse`

How to convert type of value in 'TF' or myLogicProc to truefalse?