incremental Shiny UI using conditionalPanel() and a text output in conditions - r

Question

I have been trying to create a Shiny UI that changes depending on the stage of data processing, but I can't figure out why my conditional panels don't pop up, and why even my text output for debugging doesn't show a value in the UI.
In this small example, I want to be able to show a panel after pressing a button, and then another one after pressing the second button. If the user presses the first button again, the second panel should disappear.
library(shiny)
ui <- fluidPage(
p("value of stage is:"),
textOutput("stage"),
actionButton("button1", "Show only the first panel"),
conditionalPanel("output.stage == 'first' || output.stage == 'second'",
p("First panel."),
actionButton("button2", "Also show the second panel")),
conditionalPanel("output.stage == 'second'",
p("Second panel."))
)
server <- function(input, output) {
stage <- reactive({"initial"})
stage <- eventReactive(input$button1, {"first"})
stage <- eventReactive(input$button2, {"second"})
output$stage <- renderText({stage()})
# make stage always available to UI
outputOptions(output, "stage", suspendWhenHidden = FALSE)
}
shinyApp(ui = ui, server = server)
I also tried using observeEvent() but that didn't help.
Edit: I am not directly using the input.button* values in my conditions because in my use case, the stage value also depends on other things happening on the server.

Answer 1

EDIT for better explanation :
You are defining stage too many times. The only one counting is the last one :
stage <- eventReactive(input$button2, {"second"})
At this point, stage is only that, so it never triggers.
Here is what you are searching for :
library(shiny)
ui <- fluidPage(
p("value of stage is:"),
textOutput("stage"),
actionButton("button1", "Show only the first panel"),
conditionalPanel("output.stage == 'first' || output.stage == 'second'",
p("First panel."),
actionButton("button2", "Also show the second panel")),
conditionalPanel("output.stage == 'second'",
p("Second panel.")),
textOutput("stage_dependant")
)
server <- function(input, output) {
button1_triggered <- reactiveVal(F)
button2_triggered <- reactiveVal(F)
observeEvent(input$button1,{
button1_triggered(!button1_triggered()) ## assigning a new value to button1_triggered : its contrary
})
observeEvent(input$button2,{
button2_triggered(!button2_triggered()) ## Invert the boolean
})
stage <- reactive({
if(!button1_triggered() & !button2_triggered()){
"intial"
} else if(button1_triggered() & !button2_triggered()){
"first"
} else if(!button1_triggered() & button2_triggered()){
"second anyways ?"
} else {
"second"
}
})
output$stage <- renderText({stage()})
# make stage always available to UI
outputOptions(output, "stage", suspendWhenHidden = FALSE)
stage_dependant <- reactive({
paste("This is a stage dependant reactive :",stage())
})
output$stage_dependant <- renderText(stage_dependant())
}
shinyApp(ui = ui, server = server)
You can search for more elegant ways to define stage but with this you should understand the principle.
Also note that the use of checkboxInput seems to be more appropriate for this functionnality.