Shiny Buttons

#' Shiny Version of TryCatch
#'
#' Use in reactive context, i.e. inside a server function only.
#'
#' @param session the app session object
#' @param expr R expression to evaluate safely
#' @return NULL
#' @export
exec_safely <- function(session, expr) {

    tryCatch(
        withCallingHandlers(
            warning=function(cnd) {
                msg <- paste(conditionMessage(cnd), sep="\n")
                shiny::showNotification(
                    ui=msg,
                    duration=10,
                    closeButton=TRUE,
                    type="warning"
                )
            },
            message=function(cnd) {
                msg <- paste(conditionMessage(cnd), sep="\n")
                shiny::showNotification(
                    ui=msg,
                    duration=5,
                    closeButton=TRUE,
                    type="message"
                )
            },
            expr
        ),

        error=function(cnd) {
            msg <- paste(conditionMessage(cnd), sep="\n")
            shiny::showNotification(
                ui=msg,
                duration=10,
                closeButton=TRUE,
                type="error"
            )
        }
    )
}

demo_exec_safely <- function() {
    stopifnot(
        require(shiny),
        require(shinydashboard)
    )

    nm <- "Demo: exec_safely"

    ui <- shinydashboard::dashboardPage(
        header=shinydashboard::dashboardHeader(title=nm),
        sidebar=shinydashboard::dashboardSidebar(),
        body=shinydashboard::dashboardBody(
            shiny::fluidRow(
                shiny::column(3, shiny::textInput("x", label="x:")),
                shiny::column(1, shiny::actionButton("btn","Click me", style = "margin-top:25px;")), # vertically aligned
                shiny::column(2, shiny::h2(shiny::textOutput("log_x_formatted")))
            )
        ),
        title=nm
    )

    server <- function(input, output, session) {
        rv <- shiny::reactiveValues()

        shiny::observeEvent(input$btn, exec_safely(session,{ # redirect warnings etc. to ShowNotification
            x <- suppressWarnings(as.numeric(input$x))
            stopifnot(is.numeric(x) && !is.na(x))
            rv[["log_x"]] <- log(x)
        }))

        output$log_x_formatted <- shiny::renderText(sprintf("%.3f", rv[["log_x"]]))
    }

    shiny::runApp(shiny::shinyApp(ui, server))
}