R: Saving plots - Cannot open image while still in RStudio -

i'm saving several plots in loop png files. works great, i've closed r. long i'm in rstudio, files have size of 0 kb , cannot opened since in use program. why that? did forget code something?

here's loop:

plotbasketandsavetodirectory<-function(basketname, savetodirectory){     basketvariables <- readvariablesfrombasket(basketname)      for(i in 1:nrow(basketvariables)){       variablecsv<-read.table(getvariablecsvpath(basketvariables[i,1]),header=true,stringsasfactors=false,sep=",")       variablecsv$date<-as.date(as.character(variablecsv$date), format="%y/%m/%d")       variablexts<-xts(variablecsv$close, order.by=variablecsv$date)       png(file=paste(savetodirectory,basketvariables[i,1],".png",sep=""))       plot(variablexts, main=basketvariables[i,1])       dev.off     } } 

in order formally end question, adding comment answer:

dev.off() function , must followed round brackets.