change default GUI callback

I have managed to solve the problem with the piece of code below, please give me your opinion is this the right way to call some routine when Layout Editor being invoked?

;;;

procedure(_defCR8I_CB(opt)
leCreateInstForm->cellName->_callback="_cr8tinstCallback()"
)

deRegUserTriggers("maskLayout" '_defCR8I_CB)

 ;;;

Also I had to introduce 1 argument to my function which is really not necessary for me but CIW issued a warning about missing arg and I added it. Can somebody clarify why is it so and what is the purpose of the arg?

The way you've done it is probably the way I'd have done it too...

Andrew

It's good to know. Now I have implemented the functionality I needed. Thank you guys, I've learnt something new.

The last thing I would like to clarify - what's the required argument for procedure which is used in deRegUserTriggers? In my case this is "opt" arg, without its definition CIW reports arg count mismatch error.

With deRegUserTriggers(), the first argument is required (the viewType), The 2nd to 4th arguments are optional, and default to nil. However, there is a check within the function to ensure that at least one non-nil argument has been passed (otherwise there's no point in calling it!), and it will error out if that's the case. You can (for example) call deRegUserTriggers("maskLayout" nil nil 'myPostInstallTrigger) and that would be OK - because the arguments are optional but positional, you need to pass nil for any argument you don't want to set - nil is the default in this case anyway (as can be seen from arglist('deRegUserTriggers) because you don't see any explicit default value for the optional arguments).

Regards,

Andrew

I must have stated it wrong way. My question is not about  the deRegUserTriggers() function itself but about function which is passed to it. In my case it is  _defCR8I_CB which does not require any arguments itself. Initially, I created it without any parameters and tried to pass it as it is:

 ;;;

procedure(_defCR8I_CB()
leCreateInstForm->cellName->_callback="_cr8tinstCallback()"
)

deRegUserTriggers("maskLayout" '_defCR8I_CB)

;;;;

 The commands worked OK but when tried to open any layout cellview CIW reported:

 *Error* _defCR8I_CB: too many arguments (0 expected, 1 given) - ((nil wasPushed nil prependList nil ... ))

 *WARNING* A Skill error occurred in function _defCR8I_CB

That's why I had to define the redundant _defCR8I_CB(opt) parameter in order to avoid the error, but I do not really understand how it works.

OK, the callback must be defined to accept a single argument. It's not optional as far as the caller is concerned. If you read the documentation on de triggers (in the manual which covers deRegUserTriggers amongst other things), you'll see that the argument is used to pass various information - for example, the window, the cellView, the action performed (e.g. whether you've pushed or popped, etc). It's a "disembodied property list". What it means however is that you must declare this argument in your function whether you need it or not - because it's going to be passed to you regardless.

Many callbacks work this way - they have a documented call signature.

Regards,

Andrew.

Good explanation, I got it. Thank you