reactive expression result different - r

Question

Sorry, I'm new for Shiny. I recently trying to use the reactive program to finish one project. But now I'm facing an issue not able to figure out why this happen.
First, I create a reactive expression which lists all files in one folder.
fullFilenames <- reactive({list.files(workDir, pattern="*.csv.gz", full.names=TRUE)})
Then, I observe a button event to trigger rescan the files in the folder and update the updateCheckboxGroupInput.
I set a breakpoint at "print("File Scaned")".
When we start the app, the Checkbox Group displays all files under folder correctly.
Then I remove/add files under working folder, then click rescan button. But the Checkbox Group does not get updated.
When program stopped at the breakpoint, I checked value "fullFilenames" and "fullFilenames()", and found that fullFilenames been updated, but not fullFilenames(). I trying to understand the logic behind two values are different and find a way how to update the Checkbox Group in a right way.
Can you please give some help on this issue?
Thank you very much.
Refer to below code:
library(shiny)
library(shinydashboard)
workDir<-c("c:/files")
setwd(workDir)
ui <- dashboardPage(
dashboardHeader(title = "Test Tool"),
dashboardSidebar(
sidebarMenu(
menuItem("Setup", tabName = "setup", icon = icon("cogs"))
)
),
dashboardBody(
tabItem(tabName = "setup",
fluidRow(
box(width = 12,
h1("Setup before generate dashboard"),
p(class = "text-muted",
br(),
"Default all files under working directory been selected, you also can choice your desired files.",
br(),
br()
),
fluidRow(
column(12, align="center",
actionButton("rescanFilesBtn","Rescan CSV Files")
)
)
)
),
fluidRow(
column(width = 12,
box(width = NULL, style = "max-height: 500px", status = "info", solidHeader = TRUE,
title = "Change raw CSV files as you like",
textInput("csvFileFilter","Desired CSV Files", placeholder = "File names, separate by semicolon"),
checkboxGroupInput("selectedFiles", "",
choiceValues = NULL,
choiceNames= NULL,
selected = NULL
)
)
)
)
)
)
)
server <- function(input, output, session) {
fullFilenames <- reactive({list.files(workDir, pattern="*.csv.gz", full.names=TRUE)})
observeEvent(input$rescanFilesBtn, {
print("Scan Files")
fullFilenames <- list.files(workDir, pattern="*.csv.gz", full.names=TRUE)
updateCheckboxGroupInput(session, "selectedFiles", choices = fullFilenames)
print("File Scaned")
})
}
shinyApp(ui, server)

Answer 1

I have modified your code so that you get an updated list after clicking the rescan button.
In the ui part I have changed your checkboxGroupInput as follows:
checkboxGroupInput("selectedFiles", "",
choices = list.files(workDir, pattern="*.csv.gz", full.names=TRUE),
selected = NULL)
This is done because the choices cannot be NULL.
I have just commented one line in your server code as your reactive value and local variable had the same name, due to which you were not getting any value for fullFilenames()
This is the modified server:
server <- function(input, output, session) {
fullFilenames <- reactive({list.files(workDir, pattern="*.csv.gz", full.names=TRUE)})
observeEvent(input$rescanFilesBtn, {
print("Scan Files")
# fullFilenames <- list.files(workDir, pattern="*.csv.gz", full.names=TRUE)
updateCheckboxGroupInput(session, "selectedFiles", choices = fullFilenames())
print("File Scaned")
})
}
Hope this helps!