Module - reactivity stops after a dozen of clicks

[aldohlys]

Dear all,
The very simple code below does not work as I would expect: when I click a couple of times up and down on qty numeric field little arrows, tableOutput display freeze and then does not change any more. Reactivity is stopped - see attached image.
The first clicks do work though, it freezes only after a dozen clicks - depending how fast one clicks

Code is:
ExampleUI <- function(id) {
tagList(
numericInput(NS(id,"qty"),"Quantity",value=0)
)
}

ExampleServer = function(id) {
moduleServer(id,
function(input,output,session) {
return(reactive({input$qty}))
})
}

ExampleDemo = function() {
ui = fluidPage(
ExampleUI("Entry"),
tableOutput("Res")
)

server = function(input,output,session) {
output$Res=renderTable(ExampleServer("Entry")())
}

shinyApp(ui,server)
}
And then execute ExampleDemo()

I run:

• RStudio 2022.12.0+353 "Elsbeth Geranium" Release (7d165dcfc1b6d300eb247738db2c7076234f6ef0, 2022-12-03) for Windows
  Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) RStudio/2022.12.0+353 Chrome/102.0.5005.167 Electron/19.1.3 Safari/537.36
• R.version returns
  platform x86_64-w64-mingw32
  arch x86_64
  os mingw32
  crt ucrt
  system x86_64, mingw32
  status
  major 4
  minor 2.2
  year 2022
  month 10
  day 31
  svn rev 83211
  language R
  version.string R version 4.2.2 (2022-10-31 ucrt)
  nickname Innocent and Trusting
• packageVersion("shiny")
  [1] ‘1.7.4’
  

[agus]

Hi Alexis

I think the main issue is that you are calling the module server function each time you change the "qty" input value (because you are defining a reactive expression there that uses input$qty). This happens because you are calling ExampleServer inside the renderTable.

You can check this by just adding some trivial print like:

ExampleServer = function(id) {
  moduleServer(id,
               function(input,output,session) {
                 print("Module server called")
                 return(reactive({input$qty}))
               })
}

and running the app. Each time you change the value, you'll see the print message in the console.

So, an easy fix to this issue is to just extract the module server call outside the render function, like this:

 
  server = function(input,output,session) {
    qty_reactive_val <- ExampleServer("Entry")
    output$Res=renderTable(qty_reactive_val())
  }
  
  shinyApp(ui,server)
}

Interestingly, if for some reason you'd like to still call the module server many times, if you use reactiveVal instead of reactive you might get away with it:

ExampleServer = function(id) {
  moduleServer(id,
               function(input,output,session) {
                 print("Module server called")
                 return(reactiveVal(input$qty))
               })
}

ExampleDemo = function() {
  ui = fluidPage(
    ExampleUI("Entry"),
    tableOutput("Res")
  )
  
  server = function(input,output,session) {
    output$Res=renderTable(ExampleServer("Entry")())
  }
  
  shinyApp(ui,server)
}

Hope this helps
Cheers!

---

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