observeenvent with two conditions - r

Question

I have tried to nest some "observe events" in Shiny to create a conditional rule.
It should go like this :
if one box is clicked display the corresponding single output when the button is clicked.
if both boxes are clicked display both outputs when the button is clicked.
but it always displays both outputs.
Any suggestion?
shinyApp(
ui = basicPage(
checkboxInput("box1", label = "Checkbox1", value = FALSE),
checkboxInput("box2", label = "Checkbox2", value = FALSE),
actionButton('buttn', 'Validate'),
verbatimTextOutput("out1"),
verbatimTextOutput("out2")
),
server = function(input, output) {
observeEvent(input$buttn, {
observeEvent(input$box1, {
output$out1 <- renderText({"Foo"})});
observeEvent(input$box2, {
output$out2 <- renderText({"bar"})})
})
}
)

Answer 1

Please note that it is bad practice to put observeEvents or reactives inside other observeEvents. See this slide and the two after it from a presentation by Joe Cheng.
One possible solution is to simply show or hide elements with the shinyjs package. A working example is given below.
Another solution is to use reactiveVal to hold the text to be displayed, and update that from your observer.
Hope this helps!
Solution 1
library(shiny)
library(shinyjs)
ui <- basicPage(
checkboxInput("box1", label = "Checkbox1", value = FALSE),
checkboxInput("box2", label = "Checkbox2", value = FALSE),
actionButton('buttn', 'Validate'),
shinyjs::hidden(div(id='div1', verbatimTextOutput("out1"))),
shinyjs::hidden(div(id='div2', verbatimTextOutput("out2"))),
useShinyjs()
)
server <- function(input, output) {
observeEvent(input$buttn, {
if(input$box1)
shinyjs::show('div1')
else
shinyjs::hide('div1')
if(input$box2)
shinyjs::show('div2')
else
shinyjs::hide('div2')
})
output$out1 <- renderText({"Foo"})
output$out2 <- renderText({"bar"})
}
shinyApp(ui,server)
Solution 2
library(shiny)
library(shinyjs)
ui <- basicPage(
checkboxInput("box1", label = "Checkbox1", value = FALSE),
checkboxInput("box2", label = "Checkbox2", value = FALSE),
actionButton('buttn', 'Validate'),
verbatimTextOutput("out1"),
verbatimTextOutput("out2")
)
server <- function(input, output) {
text1 <- reactiveVal(NULL)
text2 <- reactiveVal(NULL)
observeEvent(input$buttn, {
ifelse(input$box1,text1('Foo'),text1(NULL))
ifelse(input$box2,text2('Bar'),text2(NULL))
})
output$out1 <- renderText({text1()})
output$out2 <- renderText({text2()})
}
shinyApp(ui,server)

Answer 2

You don't need the extra event observers. Just observe the button click and use standard R conditional logic to adjust the output based on the checkboxes.
shinyApp(
ui = basicPage(
checkboxInput("box1", label = "Checkbox1", value = FALSE),
checkboxInput("box2", label = "Checkbox2", value = FALSE),
actionButton('buttn', 'Validate'),
verbatimTextOutput("out1"),
verbatimTextOutput("out2")
),
server = function(input, output) {
observeEvent(input$buttn, {
if (input$box1) {
output$out1 <- renderText({"Foo"})
}
if (!input$box1) {
output$out1 <- renderText({NULL})
}
if (input$box2) {
output$out2 <- renderText({"Bar"})
}
if (!input$box2) {
output$out2 <- renderText({NULL})
}
})
}
)