1. 光泽：modalDialog或showNotification
2. shinyjs：alert
3. shinyBS：bsAlert —尝试运行bsExamples("Alerts")为例

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下面是这些功能的示例的示例应用。请注意，shinyjs和shinyBS需要向UI和服务器添加语句，但modalDialog只需要在服务器上添加语句。 session也需要包含在shinyBS的服务器功能中才能使用。

library(shiny) 
library(shinyjs) 
library(shinyBS) 

ui <- fluidPage(
    tags$style(HTML(" 
        input:invalid { 
        background-color: #FFCCCC; 
        }")), 
    #### Set up shinyjs #### 
    useShinyjs(), 

    ### shinyBS ### 
    bsAlert("alert"), 

    numericInput("myValue", "My Variable", min = 0, max = 1, value = 0.5), 
    numericInput("myValue2", "My Variable2", min = 0, max = 3, step = 0.5, value = 0.5), 
    textOutput("text"), 
    textOutput("text2") 
    ) 

server <- function(session, input, output) { 
    output$text <- renderText({ 

     ### shinyBS ### 
     if(!(is.na(input$myValue)) && (input$myValue > 1 | input$myValue < 0)) { 
      createAlert(session, "alert", "myValueAlert", title = "shinyBS: Invalid input", 
         content = "'My Variable' must be between 0 and 1", style = "danger") 
     } else { 
      closeAlert(session, "myValueAlert") 
      return(input$myValue) 
     } 
     }) 
    output$text2 <- renderText(input$myValue2) 

    ### modalDialog ### 
    observeEvent(input$myValue, { 
     if(!is.na(input$myValue) && (input$myValue > 1 | input$myValue < 0)) { 
      showModal(modalDialog(
       title = "modalDialog: Invalid input", 
       "'My Variable' must be between 0 and 1" 
      )) 
     } 
    }) 

    ### shinyjs ### 
    observeEvent(input$myValue, { 
     if(!(is.na(input$myValue)) && (input$myValue > 1 | input$myValue < 0)) { 
      alert("shinyJS: 'My Variable' must be between 0 and 1") 
     } 
    }) 

} 

shinyApp(ui, server)