CODEWITHSUNDEEP
rshinyevent-handlingshiny-reactivity
nilsole
nilsole

Reputation: 1723

Change reactive expression, keep observer

How can I overwrite/re-define a reactive expression, while keeping all observers to that expression intact?

Below example is intended to make the observer listen to a button click, but only after the button has been clicked once. Before that, the observer should react to a numeric input field. (Please note that I would like the observer untouched if possible. I would like to re-define the reactive expression instead.)

library(shiny)

ui <- fluidPage(
      numericInput(inputId="some_numbers",value=8,label = "Enter a number:"),
      actionButton(inputId = "button1",label="Update reactive expression")
)

server <- function(input, output, session) {

  my_reactive_expr <- reactive({
    input$some_numbers
  })

  observeEvent(my_reactive_expr(),{
    print("reactive value change detected!")
  })

  observeEvent(input$button1,{
    my_reactive_expr <<- reactive({
      input$button1
    })
  })

}

shinyApp(ui = ui, server = server)

Upvotes: 0

Views: 717

Answers (1)

Tonio Liebrand
Tonio Liebrand

Reputation: 17689

Like written in the comments i would suggest sthg like:

my_reactive_expr <- reactive({ 
    if(!input$button1) return(input$some_numbers)
    input$button1 
  })

The full app would read:

library(shiny)

ui <- fluidPage(
  numericInput(inputId="some_numbers",value=8,label = "Enter a number:"),
  actionButton(inputId = "button1",label="Update reactive expression")
)

server <- function(input, output, session) {

    my_reactive_expr <- reactive({ 
      if(!input$button1) return(input$some_numbers)
      input$button1 
    })

  observeEvent(my_reactive_expr(),{
    print("reactive value change detected!")
  })

  observeEvent(input$button1,{
    my_reactive_expr <<- reactive({
      input$button1
    })
  })

}

shinyApp(ui = ui, server = server)

Like that you can avoid overwriting the reactive function.

Upvotes: 2

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