CODEWITHSUNDEEP
rshiny
djc55
djc55

Reputation: 555

How to stop actionButton counter at zero?

I have a shiny app which outputs the sum of clicks for two action buttons {+1, -1}. Can someone tell me how I can make the minimum value of the counter stop at zero. For example, if the first two clicks from a new session are Remove1 and Remove 1, the output will be 0, rather than -2?

library(shiny)

ui <- fluidPage(
  actionButton("add", "Add 1"),
  actionButton("remove", "Remove 1"),
  textOutput("counter")
)

server <- function(input, output, session) {
  output$counter <- renderText(
    input$add + input$remove * -1
  )
}

shinyApp(ui, server)

Upvotes: 1

Views: 58

Answers (1)

HubertL
HubertL

Reputation: 19544

It seems you can not change the value of an actionButton.

Instead you can use reactiveVal() like this:

server <- function(input, output, session) {
  total <- reactiveVal( 0 )
  observeEvent( input$add, total( total() + 1 ))
  observeEvent( input$remove, total( max( 0, total() - 1 )))
  
  output$counter <- renderText( total() )
}

Upvotes: 1

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