r - bindEvent 似乎消除了对输入的依赖

Question

我想要一个用于生成输出的Plot按钮。这很好用。我遇到的麻烦是，当我更改输入时，我希望绘图变得无效，并停止显示。

预期行为:

1. 应用加载
2. 用户选择垃圾箱数量
3. 用户点击绘图按钮
4. 绘图已渲染
5. 用户更改垃圾箱数量
6. Shiny 删除了绘图，因为垃圾箱已更改
7. 用户点击绘图按钮
8. 绘图已渲染

实际行为:

1. 应用加载
2. 用户选择垃圾箱数量
3. 用户点击绘图按钮
4. 绘图已渲染
5. 用户更改垃圾箱数量
6. Shiny 什么都不做——保留陈旧的情节
7. 用户点击绘图按钮
8. 绘图已渲染

正如您在此屏幕截图中所看到的，bin 已设置为较小的值，并且 30 bin 直方图仍然显示:

在检查依赖关系图时，我注意到上面的第 5 步，input$bins 和 bindEvent 之间的关系变为灰色(参见图片)，最终停止output$distPlot 来自无效和重新计算。

我怀疑这一步是我想避免发生的:

这是代表

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),
            actionButton('plot', 'Plot')
        ),

        # Show a plot of the generated distribution
        mainPanel(
           plotOutput("distPlot")
        )
    )
)

x = faithful[,2]
# Define server logic required to draw a histogram
server <- function(input, output) {
    bins <- reactive({
      seq(min(x), max(x), length.out = input$bins + 1)
    }) %>%
      bindEvent(input$plot)

    output$distPlot <- renderPlot({
        # generate bins based on input$bins from ui.R

        # 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)

Answer 1

可以使用reactiveVal实现所需的行为:

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),
      actionButton('plot', 'Plot')
    ),
    
    # Show a plot of the generated distribution
    mainPanel(
      plotOutput("distPlot")
    )
  )
)

x = faithful[,2]
# Define server logic required to draw a histogram
server <- function(input, output, session) {
  
  bins <- reactiveVal(NULL)
  
  observeEvent(input$plot, {
    bins(seq(min(x), max(x), length.out = input$bins + 1))
  })
  
  observeEvent(input$bins, {
    bins(NULL)
  })
  
  output$distPlot <- renderPlot({
    req(bins())
    # 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)