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* feat: Add `onUnhandledError()` * docs(NEWS): Update previous news item * docs(onUnhandledError): Add example * docs(MockShinySession): Fix unhandledErrorCallbacks private field docs * feat: Handle non-fatal unhandled errors, too * docs(onUnhandledError): Add more detailed documentation * `devtools::document()` (GitHub Actions) * docs: Small edits
112 lines
3.5 KiB
R
112 lines
3.5 KiB
R
% Generated by roxygen2: do not edit by hand
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% Please edit documentation in R/shiny.R
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\name{onFlush}
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\alias{onFlush}
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\alias{onFlushed}
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\alias{onSessionEnded}
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\alias{onUnhandledError}
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\title{Add callbacks for Shiny session events}
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\usage{
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onFlush(fun, once = TRUE, session = getDefaultReactiveDomain())
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onFlushed(fun, once = TRUE, session = getDefaultReactiveDomain())
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onSessionEnded(fun, session = getDefaultReactiveDomain())
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onUnhandledError(fun, session = getDefaultReactiveDomain())
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}
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\arguments{
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\item{fun}{A callback function.}
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\item{once}{Should the function be run once, and then cleared, or should it
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re-run each time the event occurs. (Only for \code{onFlush} and
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\code{onFlushed}.)}
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\item{session}{A shiny session object.}
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}
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\description{
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These functions are for registering callbacks on Shiny session events.
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\code{onFlush} registers a function that will be called before Shiny flushes the
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reactive system. \code{onFlushed} registers a function that will be called after
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Shiny flushes the reactive system. \code{onUnhandledError} registers a function to
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be called when an unhandled error occurs before the session is closed.
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\code{onSessionEnded} registers a function to be called after the client has
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disconnected.
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These functions should be called within the application's server function.
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All of these functions return a function which can be called with no
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arguments to cancel the registration.
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}
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\section{Unhandled Errors}{
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Unhandled errors are errors that aren't otherwise handled by Shiny or by the
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application logic. In other words, they are errors that will either cause the
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application to crash or will result in "Error" output in the UI.
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You can use \code{onUnhandledError()} to register a function that will be called
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when an unhandled error occurs. This function will be called with the error
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object as its first argument. If the error is fatal and will result in the
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session closing, the error condition will have the \code{shiny.error.fatal} class.
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Note that the \code{onUnhandledError()} callbacks cannot be used to prevent the
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app from closing or to modify the error condition. Instead, they are intended
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to give you an opportunity to log the error or perform other cleanup
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operations.
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}
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\examples{
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\dontshow{if (interactive()) (if (getRversion() >= "3.4") withAutoprint else force)(\{ # examplesIf}
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library(shiny)
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ui <- fixedPage(
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markdown(c(
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"Set the number to 8 or higher to cause an error",
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"in the `renderText()` output."
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)),
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sliderInput("number", "Number", 0, 10, 4),
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textOutput("text"),
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hr(),
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markdown(c(
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"Click the button below to crash the app with an unhandled error",
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"in an `observe()` block."
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)),
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actionButton("crash", "Crash the app!")
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)
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log_event <- function(level, ...) {
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ts <- strftime(Sys.time(), " [\%F \%T] ")
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message(level, ts, ...)
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}
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server <- function(input, output, session) {
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log_event("INFO", "Session started")
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onUnhandledError(function(err) {
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# log the unhandled error
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level <- if (inherits(err, "shiny.error.fatal")) "FATAL" else "ERROR"
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log_event(level, conditionMessage(err))
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})
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onStop(function() {
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log_event("INFO", "Session ended")
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})
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observeEvent(input$crash, stop("Oops, an unhandled error happened!"))
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output$text <- renderText({
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if (input$number > 7) {
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stop("that's too high!")
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}
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sprintf("You picked number \%d.", input$number)
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})
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}
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shinyApp(ui, server)
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\dontshow{\}) # examplesIf}
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}
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\seealso{
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\code{\link[=onStop]{onStop()}} for registering callbacks that will be
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invoked when the application exits, or when a session ends.
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}
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