为什么我的动作按钮会显示ggplot情节？

Question

以下是我的闪亮应用程序的代码：

library(shiny)
library(leaflet)
library(DT)
library(ggplot2)
library(dplyr)

r_colors <- rgb(t(col2rgb(colors()) / 255))
names(r_colors) <- colors()

plotdata <- read.csv("C:/Users/Anatoly/Documents/Collatz/RenameLater/RenameLater/MapsAndSuch/RShinyCoral.csv")
parguera <- read.csv("C:/Users/Anatoly/Documents/Collatz/RenameLater/RenameLater/MapsAndSuch/RShinyCoral.csv")
parguera <- select(parguera, 5:8)
colnames(parguera) <- c("Year", "1998 Expedition", "Year", "2004 Expedition")
monaisland <- read.csv("C:/Users/Anatoly/Documents/Collatz/RenameLater/RenameLater/MapsAndSuch/RShinyCoral.csv")
monaisland <- select(monaisland, 1:2)
colnames(monaisland) <- c("Year", "Mona Island RLI")
islacatalina <- read.csv("C:/Users/Anatoly/Documents/Collatz/RenameLater/RenameLater/MapsAndSuch/RShinyCoral.csv")
islacatalina <- select(islacatalina, 3:4)
colnames(islacatalina) <- c("Year", "Isla Catalina RLI")



ui <- fluidPage(
    verticalLayout(
    titlePanel("NOAA Coral Luminescence Data (RLI, 5-year Running Average)"),
  leafletOutput("mymap"),
  p(),
  actionButton("laparguera", "La Parguera Data"),
  actionButton("mona", "Mona Island Data"),
  actionButton("isla", "Isla Catalina Data"),
  actionButton("visualize", "Visualize Data"),
  DT::dataTableOutput('tbl')
)
)

server <- function(input, output, session) {

  output$mymap <- renderLeaflet({
    leaflet() %>%
      addTiles() %>%
      addMarkers(lat = 17.95, lng = - 67.05, popup = "La Parguera ") %>%
      addMarkers(lat = 18.00, lng = -67.50, popup = "Mona Island") %>%
      addMarkers(lat = 18.2, lng = -69.00, popup = "Isla Catalina")
  })
  observeEvent(input$laparguera, {
    output$tbl <- DT::renderDataTable(DT::datatable(parguera, options = list(pagelength = 25)))
  })
  observeEvent(input$mona, {
    output$tbl <- DT::renderDataTable(DT::datatable(monaisland, options = list(pagelength = 25)))
  })
  observeEvent(input$isla, {
    output$tbl <- DT::renderDataTable(DT::datatable(islacatalina, options = list(pagelength = 25)))
  })
  output$visualize <- renderPlot( {
    gplot <- ggplot(data = plotdata) +
    geom_point(mapping = aes(x = Year2, y = RLIMona), na.rm = TRUE)
    print(gplot)
  })
}

shinyApp(ui, server)

我的问题是，为什么赢得＆＃34;可视化＆＃34;按钮显示gplot？请注意，gplot本身会创建一个图（我检查过）。我知道情节是毫无意义的，我只想弄清楚如何使用renderPlot。

如果这是一个简单的问题，我道歉。

感谢。