About shiny branch processing using outputUI - r

Question

We are currently developing Shiny APP.
When Option A or Option B is selected from pickerinput
If you select Option A, an open file dialog opens. Then select the text file. When I select a text file, I want the title of the text file to be displayed.
When I select OptionB, I want to display nothing and do nothing.
I wrote a sample codee.
library(shiny)
library(shinyWidgets)
library(shinyFiles)
ui <- fluidPage(
pickerInput(
inputId = "Pi1",
label = "SELECT!!",
choices = list(c("OptionA"),
c("OptionB")),
options = list(`actions-box` = TRUE,size = 7),
multiple = FALSE,
),
uiOutput("button"),
uiOutput("Message")
)
server <- function(input, output, session) {
OutputUi_func(input,output)
observeEvent(input$file, {
volumes <- c("Documents"=Sys.getenv("HOME"))
shinyFileChoose(input,'file', session=session,roots=volumes, filetypes=c('', 'txt'))
if(length(input$file) <= 1) return({})
fname <- unlist(input$file)
fname <- c(fname[2][1])
ftitle <- "FileName："
fname <- paste0(ftitle,fname)
output$filename <- renderText({
paste0(fname)
})
})
}
OutputUi_func <- function(input,output){
output$button <- renderUI({
req(input$Pi1)
if(input$Pi1 %in% c("OptionA")){
shinyFilesButton('file', 'Read File', 'select file', FALSE)
}else return(NULL)})
output$Message <- renderText({
req(input$Pi1)
if(input$Pi1 %in% c("OptionA")){
textOutput("filename")
}else return(NULL)})
}
shinyApp(ui, server)
The code has a problem.
・When I execute the code, I get an error about "cat".
・ Even if you select a text file,The file title is not displayed.
What should I do to avoid the above two errors?

Answer 1

Try :
library(shiny)
library(shinyWidgets)
library(shinyFiles)
ui <- fluidPage(
pickerInput(
inputId = "Pi1",
label = "SELECT!!",
choices = list(c("OptionA"),
c("OptionB")),
options = list(`actions-box` = TRUE,size = 7),
multiple = FALSE,
),
uiOutput("button"),
uiOutput("Message")
)
server <- function(input, output, session) {
OutputUi_func(input,output)
observeEvent(input$file, {
if(input$Pi1 %in% "OptionB") return(NULL)
volumes <- c("Documents"=Sys.getenv("HOME"))
shinyFileChoose(input,'file', session=session,roots=volumes, filetypes=c('', 'txt'))
if(length(input$file) <= 1) return(NULL)
output$Message <- renderText({
if(length(input$file) <= 1 || input$Pi1 %in% "OptionB") return(NULL)
sprintf("FileName：%s", unlist(input$file$files)[[3]])
})
})
}
OutputUi_func <- function(input,output){
output$button <- renderUI({
if(input$Pi1 %in% "OptionA")
shinyFilesButton('file', 'Read File', 'select file', FALSE)
else return(NULL)
})
}
shinyApp(ui, server)