How can I detect when a text field changes in Cocoa-Applescript?

Why not just check the text field in the method that is called when the send button is pressed and if the field is blank just ignore it?

So your looking to be called each time a single char is typed in a text field?

You are looking for NSControl's controlTextDidEndEditiing: delegate method.

red_menace answered your actual question however in your first post this is what you wrote:

I have to prevent the user from sending a blank message to all contacts, so I have to change the button's setEnabled.

preventing a blank message from going out can be done by checking the text field once the users presses return or the send button and is a lot more efficient then checking for each typed char.

You'll get better responses to your questions and save everyone's time if you can actually ask the question that you want answered and supply all the relevant information up-front.

And could you do us all a favor and trim the tags you add to tour posts. Makes it a pain when reading here on a mobile device.

A specific text field is not used in the handler call - the delegate method is called for all text fields. In the case where you have several text fields, you can get the notification's object, for example:

oncontrolTextDidChange_(aNotification) -- a text field changed, so check it out

setthisTextFieldtoaNotification's object() -- the current control being changed

settheTexttothisTextField's stringValue()

logtheText

-- whatever

endcontrolTextDidChange_

Note that you need to connect the text field's delegate outlet to your AppDelegate (or whatever class you are using for the delegate).

Help I got an error:

-[NSTextField object]: unrecognised selector sent to instance 0x6080001816c0

Please Help!

You should start a new topic with your particular problem, since the specific details in your situation would be different and your reply doesn't add to solving the OP's (solved) problem.

With that said, the "unrecognised selector" error message usually means that the message (handler call) sent to an object can't be found, which could be a result of misspelling (including capitalization, since Cocoa methods are case sensitive) or a wrong or missing object (e.g. trying to use a textField method on a button, or trying to use a method on an object that hasn't been created).