R闪亮: uiOutput中的条件actionButton

Question

我有两个actionButtons，允许通过数字1-6导航。然而，我希望只有在数字1显示时才删除“后退”按钮(否则保留)，而在数字6上删除“下一步”按钮(并保留整个数字1-5)，以便为序列的开始和结束提供直观的帮助。

请看我在底部的不成功代码(#被注释掉了，因为它阻止了从数字2到5的成功转换)。

如何有条件地呈现这些按钮？

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，演示如何在值为1时删除back按钮，在值为6时删除next按钮。从这个工作示例中，您可以调整代码以类似的方式工作：

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)

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