How to update UI on file change

问题

Hello I'm building a shinydashboard using several excel files.

I inserted links to these files in the footer of the box and I want to refresh the shinydashboard when changing something in my excel file. I don't want to run the whole R code each time.

How can I re-render the Output once the file content changes?

Here an example:

sidebar <- dashboardSidebar(
sidebarMenu( menuItem("Hello", tabName = "Hello", icon = icon("dashboard"))
          ))

body <- dashboardBody(
 tabItems(

tabItem(tabName = "Hello",


        box(title = "my file", 
            footer = a("df.xlsx", href="df.xlsx" ) ,
            DT::dataTableOutput("df1"),style = "font-size: 100%; overflow: auto;",
            width = 12, hight = NULL, solidHeader = TRUE, collapsible = TRUE, collapsed = TRUE, status = "primary")
)))


ui <- dashboardPage(
 dashboardHeader(title = "My Dashboard"),
 sidebar,
body)


server <- function(input, output) {
  output$df1 <- renderDataTable({ 
df <- read_excel("df.xlsx")
DT::datatable(df, escape = FALSE, rownames=FALSE,class = "cell-border",
              options =list(bSort = FALSE, paging = FALSE, info = FALSE)
  )
  })
}



shinyApp(ui, server)

回答1:

To monitor the change in a file you could use the cheksum of the file like this:

library(shiny)
library(digest)

# Create data to read
write.csv(file="~/iris.csv",iris)

shinyApp(ui=shinyUI(
  fluidPage(
    sidebarLayout(
      sidebarPanel(
        textInput("path","Enter path: "),
        actionButton("readFile","Read File"),
        tags$hr()
      ),
      mainPanel(
        tableOutput('contents')
      )))
),
server = shinyServer(function(input,output,session){
  file <- reactiveValues(path=NULL,md5=NULL,rendered=FALSE)

  # Read file once button is pressed
  observeEvent(input$readFile,{
    if ( !file.exists(input$path) ){
      print("No such file")
      return(NULL)
    }
    tryCatch({
      read.csv(input$path)
      file$path <- input$path
      file$md5  <- digest(file$path,algo="md5",file=TRUE)
      file$rendered <- FALSE
    },
    error = function(e) print(paste0('Error: ',e)) )
  })

  observe({
    invalidateLater(1000,session)
    print('check')

    if (is.null(file$path)) return(NULL)

    f   <- read.csv(file$path)
    # Calculate ckeksum
    md5 <- digest(file$path,algo="md5",file=TRUE)

    # If no change in cheksum, do nothing
    if (file$md5 == md5 && file$rendered == TRUE) return(NULL)

    output$contents <- renderTable({

      print('render')
      file$rendered <- TRUE
      f
    })
  })

}))

回答2:

If I understand the question correctly, I'd say you need the reactiveFileReader function.

Description from the function's reference page:

Given a file path and read function, returns a reactive data source for the contents of the file.

The file reader will poll the file for changes, and once a change is detected the UI gets updated reactively.

Using the gallery example as a guide, I updated the server function in your example to the following:

server <- function(input, output) {                                                                                                                                                                                                                                   
  fileReaderData <- reactiveFileReader(500,filePath="df.xlsx", readFunc=read_excel)
  output$df1 <- renderDataTable({                                                                                                                                                                                                                                              
    DT::datatable(fileReaderData(), escape = FALSE, rownames=FALSE,class = "cell-border",                                                                                                                                                                                      
              options =list(bSort = FALSE, paging = FALSE, info = FALSE)                                                                                                                                                                                                       
  )                                                                                                                                                                                                                                                                            
  })                                                                                                                                                                                                                                                                           
}

With that, any changes I saved to 'df.xlsx' were propagated almost instantly to the UI.

来源：https://stackoverflow.com/questions/33480206/how-to-update-ui-on-file-change

标签

shinydashboard