Toggle a gbutton in gWidgets2

Question

I am creating a gbutton in gWidgets2 which will toggle between "go" and "stop" when it will be clicked.

I am following this example: toggling a group of icons in gWidgets

My Code:

library(gWidgets2)
library(gWidgets2RGtk2)
options(guiToolkit="RGtk2")

w= gwindow()
g1 <- ggroup(horizontal=TRUE, cont=w)
icon <- gbutton('go', container = g1)
state <- FALSE # a global
changeState <- function(h,...) {
  if(state) {
    svalue(icon) <- "go"
  } else {
    svalue(icon) <- "stop"
  }
  state <<- !state
}
addHandlerClicked(icon, handler=changeState)

It creates a button and toggle between "go" and "stop" when it is clicked. But the problem is I have to click two times to toggle. I want it should toggle between "go" and "stop" on one click.

Hmm, this is odd. For some reason the callback is being called twice. I can replicate my mac. I wonder if this is OS specific. What OS are you using? (This works as intended under tcltk) — jverzani, Aug 30 '19 at 16:20
My guess is svalue<- invokes the changehandler, so it is called twice. To avoid that, annoyingly, there is block_handler and unblock_handler functions that can wrap the code within the callback. — jverzani, Aug 31 '19 at 11:58

score 1 · Accepted Answer · answered Sep 02 '19 at 09:30

You can use blockHandlers() and unblockHandlers() functions to avoid this issue.

w= gwindow()
g1 <- ggroup(horizontal=FALSE, cont=w)
icon <- gbutton("go", container = g1)
#icon <- gimage(reject,cont=g1)
state <- FALSE # a global
addHandlerClicked(icon, function(h,...) {
  #
  if(!state) {
    blockHandlers(icon)
    svalue(icon) <- "stop"
    unblockHandlers(icon)
  } else {
    blockHandlers(icon)
    svalue(icon) <- "go"
    unblockHandlers(icon)
  }
  state <<- !state
})

I tried this and it works for me.

Great. A bit cleaner to wrap the if/else block, rather than each result, but that is the pattern to use. — jverzani, Sep 02 '19 at 21:04

Toggle a gbutton in gWidgets2

1 Answers1