How to return value from a function in gwidgets

Question

I have the following code to select the input and output folders' directories.

require(gWidgets2RGtk2)

input=NULL
win = gwindow("Stage 1")
g = ggroup(horizontal=FALSE,cont=win)
  g1=ggroup(cont=g)
    svalue(input)<-gbutton("Input folder",cont=g1,expand=TRUE,handler=function(...) {
      input=gfile(type="selectdir")
      gmessage(paste0("Input directory set to ",input))
      input
    })
g2=ggroup(cont=g)
    gbutton("Ouput folder",cont=g2,expand=TRUE,handler=function(...) {
      output=gfile(type="selectdir")
      gmessage(paste0("Output directory set to ",output))
    })

However when run, the code does not return the input and output folder directories. Can anyone show me what I am doing wrong here?

The handlers are called asynchronously, so they don't really have meaningful return values. Rather you must assign the value to a variable within the function body. This assigment needs to happen outside of the scope of the handler, so is done via an environment, `<<-`, or `assign` — jverzani, Jan 14 '14 at 15:40

score 5 · Accepted Answer · answered Jan 15 '14 at 20:38

To elaborate on my comment, here is an example using both an environment and <<-

require(gWidgets2)
options(guiToolkit="RGtk2")

input <- NULL                           # global
e <- new.env()                          # environment

win = gwindow("Stage 1")
g = ggroup(horizontal=FALSE,cont=win)

gbutton("Input folder",cont=g,handler=function(...) {
  value <- gfile(type="selectdir")
  gmessage(paste0("Input directory set to ",value))
  ## assign via <<-
  input <<- value
  ## assign to an environment
  e$input <- value
})

gbutton("What is stored?", cont=g, handler=function(...) {
  print(sprintf("The global variable has %s", input))
  print(sprintf("The environment stores %s", e$input))
})

How to return value from a function in gwidgets

1 Answers1