Unhandled error in observer: cannot add bindings to a locked environment

[happyshows]

Hi,

I have observe the following error with the 0.11.1.9xxx. The error went away as I switched back to the stable version on CRAN. This error will pop up to basically any attempt to create a reactivevalueslist. No matter outside or inside the function(input, output, session)

Warning in run(timeoutMs) : Unhandled error in observer: cannot add bindings to a locked environment

my code in server.R svr <- reactiveValues(conCount = 0) function(input, output, session) { ... }

[wch]

Could you supply a full reproducible example?

[happyshows]

@wch I tried to isolate the problem and it seems that in 0.11.1, I can modify session object within function(session,input,output) but with 0.11.1.9, system will throw error : Unhandled error in observer: cannot add bindings to a locked environment

library(shiny)

svr <- reactiveValues(conCount = 0)

server <- function(session,input, output) { session$lockDisabled <- NULL }

ui <- fluidPage( h6('') )

shinyApp(ui = ui, server = server)

[wch]

Oh, I see what you're doing. That's the expected behavior - you aren't allowed to add new fields to the session object.

Why are you trying to do that? There is likely another solution for what you're trying to do.

[jcheng5]

If you want a session-scoped variable, just declare it as a normal variable inside of the Shiny server function. See this article: http://shiny.rstudio.com/articles/scoping.html

To assign to such variables from inside of observers and whatnot, use <<- for assignment instead of <-. (These are just normal R lexical scoping https://www.stat.auckland.ac.nz/~ihaka/downloads/lexical.pdf semantics, nothing particular to Shiny.)

On Wed, May 6, 2015 at 9:38 AM, Winston Chang notifications@github.com wrote:

Oh, I see what you're doing. That's the expected behavior - you aren't allowed to add new fields to the session object.

Why are you trying to do that? There is likely another solution for what you're trying to do.

— Reply to this email directly or view it on GitHub https://github.com/rstudio/shiny/issues/822#issuecomment-99531945.

[happyshows]

thanks, I think I understand the root cause but was a bit surprised that it didn't throw any error before.

[SJCaldwell]

To anyone curious, the same error is thrown if you're building a custom R object and try to assign a value to a variable you didn't initialize.

[lpatruno]

Thanks for that info @SJCaldwell