将r Shiny ObserveEvent与downloadHandler一起使用

Question

I am challenged by the process of using an observer to observe the action of creating a CSV file for download. I think that the R-Studio documentation states that eventExpr may be a "complex expression inside curly braces." Is this a valid eventExpression? I am using this construct 5 times, and all five conditions are triggered when my shinyApp initiates.

    observeEvent(
        {
        ### Observe the download handler preparing for CSV download
        output$Wire_Centers.csv <- downloadHandler(
            filename = "Wire_Centers.csv",
            content = function(file) {
                write.table(WC_List_2(), file, row.names=FALSE, col.names = TRUE, sep=',') ### end write.table
                } # End content function
            ) # End downloadHandler
            }, { # End observered event, start log
        logUse("WC_Download")
        }) # end observeEvent output condition

Any ideas or suggestions?

Answer 1

As you noted, all five are being called at startup. The code isn't tied to an input$ or other change, so it just runs and it reports that it started . Consider if you want it to report after the download finishes or if you want to run the code on user input.

Answer 2

I accomplished adding the activity log action by adding the log function call as the first clause of the content function for the downloadHandler. The call logUse("WC_Download") operates as required, and the activity log is appropriately augmented.

    output$Wire_Centers.csv <- downloadHandler(
        filename = "Wire_Centers.csv",
        content = function(file) {
            logUse("WC_Download")
            write.table(WC_List_2(), file, row.names=FALSE, col.names = TRUE, sep=',') ### end write.table
            }, # End content function
        ) # End downloadHandler