R Shiny：uiOutput 中的条件操作按钮

Question

我有两个actionButtons 允许在数字 1-6 中导航。但是，我希望仅在显示数字 1 时删除“后退”按钮（但否则保留），并在数字 6 上删除“下一步”按钮（并保留在数字 1-5 中），以便提供关于序列开始和结束的视觉辅助。

请在底部查看我不成功的代码（#commented out 因为它会阻止成功过渡到数字 2-5）。

如何有条件地渲染这些按钮？

library(shiny)
library(shinyWidgets)



ui <- fluidPage(
  
  fluidRow(
    div(column(5,uiOutput("back"),align= "right")),
    div( column(5,uiOutput("next_q")),align = "left")),
  fluidRow(  
    column(5,offset = 3,id = "qa1", uiOutput("ui_q1"),br(),br(),
    )),
)

server <- function(input, output, session) {
  qbank=reactive(as.vector(c(1,2,3,4,5,6)))

  
  values <- reactiveValues()
  values$count <- 1
  myReactives <- reactiveValues(reactInd = 0)
  
  observe({
    input$next_q
    myReactives$reactInd <- 1
  })
  
  observe({
    input$back
    myReactives$reactInd <- 2
  })
  
  
  ntext <- eventReactive(input$next_q,{
    if(values$count != length(qbank())){
      values$count <- values$count + 1
      return(qbank()[values$count])
    }
    else{
      return(qbank()[length(qbank())])
    }
  })
  
  
  btext <- eventReactive(input$back,{
    if(values$count != 1){
      values$count <- values$count - 1
      return(qbank()[values$count])
    }
    else{
      return(qbank()[1])
    }
  })
  
  q <- reactive({
    if(input$next_q == 0){
      return(qbank()[1])
    }
    else if(myReactives$reactInd==1) return(
      ntext())
    else if(myReactives$reactInd==2)return(
      btext())
  })  
  
  q1 = reactive((q()[1]))
  output$q1 = renderText(q1())
  output$ui_q1 = renderUI(textOutput("q1"))
  
  
  output$back = renderUI({
    
    ## I cannot get the following if statement to function correctly
   # if(values$count==1) return (NULL)
   # else
      (actionButton("back","back"))})
  
  
  output$next_q = renderUI(    
    
    ## I cannot get the following if statement to function correctly
   # if(values$count==length(qbank()))
   # return (NULL)
   # else
      actionButton("next_q","next"))
}

shinyApp(ui, server)

谢谢

Answer 1

我构建了一个玩具示例，演示如何在 1 时删除后退按钮，并在 6 时删除下一个按钮。从这个工作示例中，您可以调整代码以类似方式工作：

library(shiny)

ui <- fluidPage(

    fluidRow(column(12,align="center",textOutput("currentNum"))),
    fluidRow(
        column(6,align="right",uiOutput("backBut")),
        column(6,align="left",uiOutput("nextBut"))
    )
    
)

server <- function(input, output) {
    
    rv <- reactiveValues(currPage=1)
    
    observeEvent(input$backButton,{
        rv$currPage <- rv$currPage - 1
    })
    
    observeEvent(input$nextButton,{
        rv$currPage <- rv$currPage + 1
    })
    
    output$currentNum <- renderText({rv$currPage})
    
    output$backBut <- renderUI({
        if(rv$currPage>1){
            actionButton("backButton","< Back")
        } 
    })
    
    output$nextBut <- renderUI({
        if(rv$currPage<6){
            actionButton("nextButton","Next >")
        } 
    })
   
}

shinyApp(ui = ui, server = server)