[R] checking for "viability" of a GUI component

[Hao Liu]

Dear All:

The question: How do I check for existance of the GUI, instead of 
checking  the variable of the GUI?

I created a log window for several applications, they will check for the 
existance of log window, if it exists, append output to it, otherwise, 
create log window and insert to it. What I found out is that if I close 
the X window of the GUI, the variable logwin still exists, confuse 
arises to other components that are supposed to use the GUI.

create.log.win <- function(inputtext){
    if(exists(is.null("logwin"))) {return} else {
        logwin <<- tktoplevel()
        logtext <<- tktext(logwin, bg="white")
        tkwm.title(logwin," Log Window")
        loglabel <- tklabel(logwin, text="Logging Analaysis Information")
        tkgrid(loglabel)
        tkgrid(logtext)
    if (is.matrix(inputtext)) {
        for (i in 1:nrow(inputtext))
            tkinsert(logtext, "end",paste(paste(inputtext[i,],collapse=" 
"),"\n",sep=""))
    }
    else tkinsert(logtext, "end",paste(inputtext,"\n",sep=""))
        export_button <- tkbutton(logwin, text = "Export Log", 
command=savelog)
        tkgrid(export_button)
    }
}

-- I understand I should bind a function to remove the varialbe with a 
close button, however, we can't stop users from closing window just by 
clicking on the upper right corner.

How do I check for existance of the GUI, instead of the variable?

Thanks