首次执行时Shiny繁忙提示不显示的问题解决需求

问题原因 #

首次启动应用时，uiOutput("busy")对应的renderUI需要等待服务器完成初始的renderPlot计算后才会渲染提示元素，但此时shiny-busy状态已经结束，导致首次执行时用户看不到繁忙提示。只有后续调整参数时，提示元素已经存在，才能正常捕捉到shiny-busy状态。

解决方案 #

直接在UI中嵌入繁忙提示的HTML代码，无需通过服务器端的renderUI生成。这样页面加载完成后提示元素就已存在，能立刻响应首次执行时的shiny-busy状态。

修改后的完整代码 #

library(shiny)

# Define UI for application that draws a histogram
ui <- fluidPage(
    # Application title
    titlePanel("Old Faithful Geyser Data"),
    # Sidebar with a slider input for number of bins 
    sidebarLayout(
        sidebarPanel(
            sliderInput("bins",
                        "Number of bins:",
                        min = 1,
                        max = 50,
                        value = 30)
        ),
        # Show a plot of the generated distribution
        mainPanel(
            # 直接嵌入繁忙提示HTML，无需uiOutput
            HTML("&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;", paste0(
                '<span data-display-if="',
                '$(\'html\').attr(\'class\')==\'shiny-busy\'',
                '">',
                '<i class="fa fa-spinner fa-spin-pulse fa-fw" style="color: #337ab7;" >busy</i>',
                '</span>'
            )),
            plotOutput("distPlot")
        )
    )
)

# Define server logic required to draw a histogram
server <- function(input, output) {
    output$distPlot <- renderPlot({
        # generate bins based on input$bins from ui.R
        x    <- faithful[, 2]
        bins <- seq(min(x), max(x), length.out = input$bins + 1)
        
        for(i in 1:10000000){# 模拟耗时计算
          log(i)
        }

        # draw the histogram with the specified number of bins
        hist(x, breaks = bins, col = 'darkgray', border = 'white',
             xlab = 'Waiting time to next eruption (in mins)',
             main = 'Histogram of waiting times')
    })
}

# Run the application 
shinyApp(ui = ui, server = server)

关键修改点 #

• 移除了服务器端的shiny_busy函数和output$busy的renderUI逻辑
• 将原shiny_busy()生成的HTML代码直接写入UI的mainPanel中，确保页面加载时提示元素已存在，能及时响应首次的shiny-busy状态

内容的提问来源于stack exchange，提问作者Steven Ouellette