Check Shiny inputs and generate warning on sidebar layout - r

Question

I'm trying to create a shiny app that checks if an email provided in the sidebar is valid (in my case I authenticate directly to an API but in the code below I just create a toy example). I know that I can generate warnings and errors for inputs using validate and need (already read the shiny site on the topic here) but on most examples the errors and warnings are shown in the mainPanel() when generating a plot or something a like.
In my case, the main layout is only static text. What I'm trying to achieve is simple: the user inputs an email I check it, if it doesn't comply I generate some warning/error but it is shown somewhere else other than the mainPanel() because in my case there's no dynamic mainPanel.
Below is an example of what I'm trying to achieve.
library(shiny)
ui <- fluidPage(
# Sidebar with a slider input for number of bins
sidebarLayout(
sidebarPanel(
textInput("email", "Email")
),
mainPanel()
)
)
# Define server logic required to draw a histogram
server <- function(input, output) {
output$email <-
renderUI({
validate(need(input$email == "",
"Introduce your email"))
validate(need(grep("gmail", input$email, value = TRUE)),
"Your email is not valid")
})
}
# Run the application
shinyApp(ui = ui, server = server)
Any idea how to achieve this? The error could be shown any where but on the mainPanel.

Answer 1

I am not 100% sure if I understand your question correctly, does the below do what you want? It displays a text message in the sidebar if one of your specified conditions is not met.
Hope this helps!
library(shiny)
ui <- fluidPage(
# Sidebar with a slider input for number of bins
sidebarLayout(
sidebarPanel(
textInput("email", "Email"),
uiOutput('email_text')
),
mainPanel()
)
)
# Define server logic required to draw a histogram
server <- function(input, output) {
output$email_text <-
renderUI({
if(input$email == ""){
return(p("Please add your gmail e-mail address."))
}
if(!grepl("gmail", input$email)){
return(p("Your email is not a gmail e-mail address!"))
}
})
}
# Run the application
shinyApp(ui = ui, server = server)