How to reset a value of fileInput in Shiny?

Question

There are already similar posts on this matter (ex. how can I update a shiny fileInput object?), but I still cannot figure out how one may force Shiny to forget a value of

Answer 1

input$file1 is cached by Shiny so will not change before next upload.

Since you want a file name variable which map to input$file1$name in most time but reset to NULL when reset button is clicked, you need to create another layer and maintain this relationship.

• You can create a variable upload_state, set it to uploaded with file upload event, and reset with reset button.

• use a reactive expression which will take input$file1$name or NULL according to upload_state value.

There is no need for the submit button.

library(shiny)
ui <- shinyUI(bootstrapPage(
  headerPanel("Reset / Submit file input example"),
  sidebarPanel(
    fileInput('file1', label = NULL),
    fluidRow(
      column(4,
             actionButton('reset', 'Reset Input')
      ))
  ),

  mainPanel(
    h4("Summary"),
    verbatimTextOutput("summary")
  )
))

server <- shinyServer(function(input, output, session) {
  values <- reactiveValues(
    upload_state = NULL
  )

  observeEvent(input$file1, {
    values$upload_state <- 'uploaded'
  })

  observeEvent(input$reset, {
    values$upload_state <- 'reset'
  })

  file_input <- reactive({
    if (is.null(values$upload_state)) {
      return(NULL)
    } else if (values$upload_state == 'uploaded') {
      return(input$file1)
    } else if (values$upload_state == 'reset') {
      return(NULL)
    }
  })

  output$summary <- renderText({
    return(paste("Uploaded file:", file_input()$name))
  })
})

shinyApp(ui = ui, server = server)

Answer 2

I know this is an old post, but you can reset the input by rebuilding it from scratch in the server.

In ui.R you can put:

...
uiOutput('file1_ui') ## instead of fileInput('file1', label = NULL)
...

And in server.R add this:

...
output$file1_ui <- renderUI({
  input$reset ## Create a dependency with the reset button
  fileInput('file1', label = NULL)
})
...