My custom gui button is getting pressed even before hitting the button.

That's because you're calling the function when you use: ?callback buttonCB(a b). You need to pass either a string to be executed, or a function object. I thought initially (based on your definition of the callback) that you wanted to use the function object way of doing this, in which case you'd change the callback to:

?callback getd('buttonCB)

but then the function would fail because the arguments are strings to the printf - you could fix that to be:

procedure(buttonCB(a b)
  printf("Button pressed - field:%L scope:%L\n"
    a b
    ;a~>value b~>value
  )
)

but given that you're assigning two variables a and b as the fields are created, I suspect this is not what you want it to do. Passing a and b to the callback doesn't make much sense because it will likely get executed out of scope - although you have a and b being global variables, so it would work - but it would be poor code. You could just change

?callback "buttonCB(a b)"

and keep your original buttonCB definition. It's not a field and scope being accessed then, so it's misleading.

Better would be to change the code like this:

procedure(Create_input_form()
  let((FORM2)
    FORM2=hiCreateLayoutForm( 
      'NPN_ 
      "NPN "

      hiCreateFormLayout( 
        'main_layout
        ?spacing 10 
        ?label_align 'center 
        ?items (list
          hiCreateStringField( 
            ?name 'SF1
            ?prompt "SF1 "

            ?editable t)
          hiCreateSeparatorField(
            ?name 'sep1)
            hiCreateStringField( 
            ?name 'SF2
            ?prompt "SF2"

            ?editable t)
          hiCreateStringField( 
            ?name 'SF3
            ?prompt "SF3"

            ?editable t)
          hiCreateButton(
            ?name 'button
            ?buttonText "Press me"

            ?callback "buttonCB(hiGetCurrentForm())"
          )

      ));main_layout
    );display_form
    hiDisplayForm(FORM2)
  )
)

procedure(buttonCB(form)
  printf("Button pressed - field1:%s field3:%s\n"
    form->SF1->value form->SF3->value
  )
)

You should also clean up your function names - with names like that you're likely to collide with some other code. Best practice is to start all your functions with a prefix, beginning with an uppercase letter so that you don't clash with other functions.

Andrew

That's because you're calling the function when you use: ?callback buttonCB(a b). You need to pass either a string to be executed, or a function object. I thought initially (based on your definition of the callback) that you wanted to use the function object way of doing this, in which case you'd change the callback to:

?callback getd('buttonCB)

but then the function would fail because the arguments are strings to the printf - you could fix that to be:

procedure(buttonCB(a b)
  printf("Button pressed - field:%L scope:%L\n"
    a b
    ;a~>value b~>value
  )
)

but given that you're assigning two variables a and b as the fields are created, I suspect this is not what you want it to do. Passing a and b to the callback doesn't make much sense because it will likely get executed out of scope - although you have a and b being global variables, so it would work - but it would be poor code. You could just change

?callback "buttonCB(a b)"

and keep your original buttonCB definition. It's not a field and scope being accessed then, so it's misleading.

Better would be to change the code like this:

procedure(Create_input_form()
  let((FORM2)
    FORM2=hiCreateLayoutForm( 
      'NPN_ 
      "NPN "

      hiCreateFormLayout( 
        'main_layout
        ?spacing 10 
        ?label_align 'center 
        ?items (list
          hiCreateStringField( 
            ?name 'SF1
            ?prompt "SF1 "

            ?editable t)
          hiCreateSeparatorField(
            ?name 'sep1)
            hiCreateStringField( 
            ?name 'SF2
            ?prompt "SF2"

            ?editable t)
          hiCreateStringField( 
            ?name 'SF3
            ?prompt "SF3"

            ?editable t)
          hiCreateButton(
            ?name 'button
            ?buttonText "Press me"

            ?callback "buttonCB(hiGetCurrentForm())"
          )

      ));main_layout
    );display_form
    hiDisplayForm(FORM2)
  )
)

procedure(buttonCB(form)
  printf("Button pressed - field1:%s field3:%s\n"
    form->SF1->value form->SF3->value
  )
)

You should also clean up your function names - with names like that you're likely to collide with some other code. Best practice is to start all your functions with a prefix, beginning with an uppercase letter so that you don't clash with other functions.

Andrew

Thank you Andrew for the response and suggestions, those really helped me a lot.

Yours

Purbayan