catch clicks on the 'x' button using Tk Tcl

Question

I'm using Tcl/Tk to build a GUI, for Linux environment and I saw that it's possible to "catch" a press on the 'x' button of the window (The button on the top right corner that closes the program).

How can I catch those events?

Answer 1

To take control of requests to delete a window, configure a suitable protocol handler:

wm protocol . WM_DELETE_WINDOW {
    if {[tk_messageBox -message "Quit?" -type yesno] eq "yes"} {
       exit
    }
}

The default behavior (i.e., if the protocol handler is the empty string) is to just destroy the toplevel to which the request was made.