Validate input parameters

[bborgesr]

We should do input validation and print a message/warning when things are off. For example, for numericInput(), we allow the min being greater than the max or the value out of the min-max range, without any indication something is off...

[bklingen]

An idea would be to have the input flash in red, like I believe it did in earlier versions of shiny and not accept the input, i.e., revert to the previous state.

Previous references for numericInput: #1593 (about accepting characters), #927, #1022

[stla]

I personally use a simple css:

input:out-of-range {
  background-color: #FFCCCC;
}

The css input:invalid also acts when the "step" is not respected, and this is not what I want in general.

[chanioman]

@stla could you elaborate a bit more how you do this?

Maybe a MWE?
thanks in advance

---

Figured it out myself. Sorry stla.

(adding it for noobs like me):

library(shiny)

ui <- fluidPage(
tags$style(HTML("
input:invalid {
background-color: #FFCCCC;
}")),

numericInput("myValue", "My Variable", min = 0, max = 1, step = 0.5, value = 0.5),
numericInput("myValue2", "My Variable2", min = 0, max = 3, step = 0.5, value = 0.5),
textOutput("text"),
textOutput("text2")
)

server <- function(input, output) {
output$text <- renderText(input$myValue)
output$text2 <- renderText(input$myValue2)
}

shinyApp(ui, server)

[MadhulikaTanuboddi]

Another potential improvement with numeric input validation. With max value set, it is possible to give a number beyond that if we clear the numeric text and type the number. For example, one of the shiny-examples, 050-kmeans-example, max is set to 9 for cluster count. However, I am able to provide any number past 9 and the cluster responds. So, as @bklingen mentioned, probably resetting to the previous value when something is off is a good idea.

[cpsievert]

Closing since we now have https://github.com/rstudio/shinyvalidate