Question

Just making a really simple Tcl/Tk program to learn, but I’m having a little trouble.

I need to make a button switch colours when clicked, so it will start red, when clicked it will turn green, and if clicked again will go back to red.

I have got it changing from red to green, but I don’t know how to make it go back the other way.
What is the best way to do this?

Answer 1

It’s not very hard (except on OSX, where this sort of thing is directly against platform UI guidelines) you just need to use a suitable callback:

button .b -background red -command [list toggleTheButton .b]
set state(.b) 1
proc toggleTheButton w {
    global state
    if {$state($w)} {
        $w configure -background green
    } else {
        $w configure -background red
    }
    set state($w) [expr {!$state($w)}]
}

Consider using a checkbutton instead when you need toggling, as it will be much more rapidly understood by the users.