Returning variable from TclTk GUI in R

Question

I've followed the TclTk example for creating a listbox to let the user choose their favorite fruit (see code below). The example prints the user's choice and that's it. However, I want to use that choice later in my script to do various things (use it in plot titles, filenames, etc.) How do I return the user's choice from a TclTk GUI to the rest of my script?

library(tcltk2)

win1 <- tktoplevel()
win1$env$lst <- tk2listbox(win1, height = 4, selectmode = "single")
tkgrid(tk2label(win1, text = "What's your favorite fruit?", justify = "left"),
padx = 10, pady =c(15, 5), sticky = "w")
tkgrid(win1$env$lst, padx = 10, pady = c(5, 10))
fruits <- c("Apple", "Orange", "Banana", "Pear", "Apricot")
for (fruit in fruits)
  tkinsert(win1$env$lst, "end", fruit)
# Default fruit is Banana.  Indexing starts at zero.
tkselection.set(win1$env$lst, 2)

onOK <- function() {
  fruitChoice <- fruits[as.numeric(tkcurselection(win1$env$lst)) + 1]
  tkdestroy(win1)
  msg <- paste0("Good choice! ", fruitChoice, "s are delicious!")
  tkmessageBox(message = msg)
}
win1$env$butOK <-tk2button(win1, text = "OK", width = -6, command = onOK)
tkgrid(win1$env$butOK, padx = 10, pady = c(5, 15))

Answer 1

How do I return the user's choice from a TclTk GUI to the rest of my script?

This depends on what you want to do

Option 1:

If you don't need the GUI anymore you destroy it after extracting the selected settings from the GUI in R variables. This is exactly what you do in the onOK "event handler" function.

You should add the following R command to wait for the tcltk window to be closed before continuing the execution of the R code after this line:

# Wait for the window to be closed
tkwait.window(win1)

You can then use the values in R variables (filled from the GUI settings in the event handler function) in your business logic e. g. by adding the business logic code at at the end of your code:

choice <- tkmessageBox(message=paste("Do you want to buy", fruitChoice, "now?"), type = "yesno", icon="question")

Option 2:

Your business logic is triggered (executed) in the event handler functions (without destroying/closing the window) to visualize the output ("state change") of the business logic.

In this GUI driven paradigm you add the business logic code into the event handler functions directly without calling tkdestroy.

For closing the windows you add "exit", "close", "cancel"... buttons. In the event handler function of these buttons you call tkdestroy.

Answer 2

There are command parameters available with listboxes (need to know which package you used for creating it). e.g there is a parameter "-selectioncommand". You can set a namespace variable to access the selected value.

e.g -selectioncommand {set ::xyz::test} this should be used while creating a widget.