Shiny : how to reset selectInput or observeEvent? - r

Question

When I open a modalDialog (by clicking a "modal" button) with a selectInput inside it, the first choice of the list is displayed and the observeEvent is automaticaly launched with this first element. That's ok.
If I choose a second element of the list, the observeEvent is launched again and that's right.
I "cancel" or "dismiss" the modalDialog and I open it again by clicking "modal" button in the main window.
The first choice of the list is displayed again and the observeEvent is automaticaly launched with this first element. That's ok.
Now I "cancel" or "dismiss" this modalDialog, without choosing any element of the selectInput.
If I open the modalDialog again, nothing happens BECAUSE the first choice is the same when I closed the modelDialog before so the observeEvent didn't detect any change so it doesn't launch the action.
Is there a way to RESET the selectInput or the observeEvent in order to "forget" which element was previously selected when the modalDialog is closed ? This MUST works even if the selectInput contain only one choice.
I tried to add an actionButton in the footer of the modalDialog in order to launch an action while closing it : it updates the selectInput with a fake value but I don't think it's a good way...
Here is a reproducible code, I set the selectInput with only one choice...
Remove the # in front of the updateSelectInput to test my workaround.
Thanx !
library(shiny)
ui <- fluidPage(
actionButton("open", "Modal")
)
server <- function(input, output, session) {
observeEvent(input$open, {
showModal(
modalDialog(
tagList(
div(id="choice",
selectInput(
"dateList", "History:",
choices = c("choice1")
)
)
)
,
footer = tagList(
actionButton("cancel","CANCEL"),
actionButton("save", "SAVE")
)
)
)
})
observeEvent( input$dateList,{
insertUI("#choice", ui=div("hello"))
})
observeEvent( input$cancel,{
removeModal()
#updateSelectInput(session, "dateList" , choices = c("fake"), selected = NULL)
})
}
shinyApp(ui, server)

Answer 1

Interesting. Here is a way which works but I don't fully like it, because it generates a JavaScript warning. But no worry, this warning is harmless.
The idea is to use a reactive value which reacts to both input$datelist and input$cancel.
reacVal <- eventReactive(list(input$dateList, input$cancel), {
runif(1)
})
observeEvent(reacVal(), {
insertUI("#choice", ui = div("hello"))
})
observeEvent(input$cancel, {
removeModal()
})
The warning is due to the facet that there is no div #choice when the cancel button is pressed.
EDIT
Here is a better way. No warning and clearer. I "reset" input$dateList by setting it to NULL when the cancel button is clicked, using some JavaScript in the onclick attribute of this button.
observeEvent(input$open, {
showModal(
modalDialog(
tagList(
div(id="choice",
selectInput(
"dateList", "History:",
choices = c("choice1", "choice2")
)
)
)
,
footer = tagList(
actionButton(
"cancel", "CANCEL",
onclick = "Shiny.setInputValue('dateList', null);"
),
actionButton("save", "SAVE")
)
)
)
})
observeEvent(input$dateList, {
insertUI("#choice", ui = div("hello"))
})
observeEvent(input$cancel, {
removeModal()
})
I choose NULL because the observer does not react to NULL (by default), that's why the previous warning does not occur here.