Re: [R-gui] gWidgets: multiple handlers using a loop?

[Michael Lawrence]

On Fri, Feb 26, 2010 at 5:15 AM, Liviu Andronic <landronim...@gmail.com>wrote:

> Dear all
> I am trying to create several sliders, each in its own container and with
> its own handler. It works fine when I create all the widgets manually, but
> gives some strange behaviour when I pass everything through a loop.
>
> ## function to be used by the handler of the slider
> count.mv.int <- function(x, start=1, end=2){
>    assign("i", x, envir = .GlobalEnv)
>    print(paste("i = ", i))
> }
> count.mv.int(2); i
>
> ## function to be used by the handler of the slider
> count.mv.let <- function(x, start=1, end=4){
>    assign("l", letters[x], envir = .GlobalEnv)
>    print(paste("l = ", l))
> }
> count.mv.let(3); l
>
> ## manually created widgets
> count.pop <- function(fun=c("count.mv.int", "count.mv.let")){
>    require(gWidgets)
>    options(guiToolkit="tcltk")
>    w <- gwindow(paste("Counters"))
>    g <- ggroup(cont=w, horizontal=T)
>    g1 <- ggroup(cont=g, horizontal=FALSE)
>    glabel(paste("'", fun[1], "'", sep=""), cont=g1)
>    h1 <- function(h,...) eval(parse(text=paste(fun[1], "(svalue(h$obj))",
> sep="")))
>    s1 <- gslider(from=formals(fun[1])$start, to=formals(fun[1])$end,
>            by=1, cont=g1, handler=h1)
>    gseparator(horizontal=FALSE, cont=g, expand=TRUE)
>    g2 <- ggroup(cont=g, horizontal=FALSE)
>    glabel(paste("'", fun[2], "'", sep=""), cont=g2)
>    h2 <- function(h,...) eval(parse(text=paste(fun[2], "(svalue(h$obj))",
> sep="")))
>    s2 <- gslider(from=formals(fun[2])$start, to=formals(fun[2])$end,
>            by=1, cont=g2, handler=h2)
> }
> ## works fine: each slider change will trigger the correct handler
> count.pop()
>
> ## widgets created through loops
> count.pop1 <- function(fun=c("count.mv.int", "count.mv.let")){
>    require(gWidgets)
>    options(guiToolkit="tcltk")
>    w <- gwindow(paste("Counters (loop)"))
>    g <- ggroup(cont=w, horizontal=T)
>    for(k in 1:length(fun)){
>        x.cont <- paste("g", i, sep="")
>        assign(x.cont, ggroup(cont=g, horizontal=FALSE))
>        glabel(paste("'", fun[k], "'", sep=""), cont=get(x.cont))
>        x.handl <- paste("h", i, sep="")
>        assign(x.handl, function(h,...) eval(parse(text=paste(fun[k],
> "(svalue(h$obj))", sep=""))))
>        x.sl <- paste("s", i, sep="")
>        assign(x.sl, gslider(from=formals(fun[k])$start,
> to=formals(fun[k])$end,
>                by=1, cont=get(x.cont), handler=get(x.handl)))
>        gseparator(horizontal=FALSE, cont=g, expand=TRUE)
>    }
> }
> ## wrong behaviour: both sliders will trigger the second handler only
> count.pop1()
>
> Could someone hint at what I am doing wrong? Thank you
> Liviu
>
>
You probably want to change the for() loop to an lapply construct, so that
you are creating a unique closure around each handler. Otherwise, they'll
both see the same value of 'k' (whatever it was set to last).


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