R Shiny bslib中layout_columns传入卡片列表时col_widths失效问题

我根据用户输入生成一组card组件，将该卡片列表传入layout_columns()时，组件被识别为单个元素，无法正确布局。具体表现为虽应用了宽度设置，但每行仅显示一个卡片。尝试传入do.call(tagList, list_of_cards)仍未解决问题。设置col_widths = rep(6, length(cats))时出现警告：

Warning: Truncating number of widths at 'md' breakpoint to match number of elements. • widths: 3 • elements: 1

可复现代码 #

library(shiny)
library(tidyverse)
library(bslib)
library(thematic)

# Define UI for application that draws a histogram
ui <- page_sidebar(
  # Set the CSS theme
  theme = bs_theme(bootswatch = "lumen",
                   version = 5
  ),
  
  # Add sidebar elements
  sidebar = sidebar(
    class = "bg-secondary",
    uiOutput("sidebar_content")
  ),
  
  uiOutput("main_content")
)

# Define server logic required to draw a histogram
server <- function(input, output) {
  
  # side bar
  output$sidebar_content <- renderUI({
    list(
      selectInput("categories",
                  "Select categories",
                  choices = c("test1", "test2", "test3"),
                  selected = c("test1", "test2", "test3"),
                  multiple  = TRUE),
      selectInput("fy",
                  "Select FY",
                  choices = c(2023, 2024, 2025),
                  selected = 2024,
                  multiple  = FALSE)
    )
  })
  
  # categories reactive
  categories <- reactive({ input$categories })
  fy <- reactive({ input$fy })
  
  # main contents
  output$main_content <- renderUI({
    req(categories())
    req(fy())
    
    # Create a list to store the card elements
    cats = categories()
    fy_selected = fy()
    cardList <- map(1:length(cats), function(i) {
      card(card_header(cats[i], class = "h6 text-success"), "sample")
    })
    
    # Return the list of card elements within layout_columns
    layout_columns(col_widths = rep(6, length(cats)),
                  do.call(tagList, cardList))
  })
}

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

会话信息 #

─ Session info ───────────────────────────────────────────────────────────────────────────────────────────────────────────────────
 setting  value
 version  R version 4.3.2 (2023-10-31 ucrt)
 os       Windows 10 x64 (build 19045)
 system   x86_64, mingw32
 ui       RStudio
 language (EN)
 collate  English_United States.utf8
 ctype    English_United States.utf8
 tz       America/New_York
 date     2024-02-01
 rstudio  2023.12.0+369 Ocean Storm (desktop)
 pandoc   NA

─ Packages ───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
! package     * version date (UTC) lib source
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[1] C:/Users/oliver/Documents/GitHub/budget_burn_rate/renv/library/R-4.3/x86_64-w64-mingw32
[2] C:/Users/oliver/AppData/Local/R/cache/R/renv/sandbox/R-4.3/x86_64-w64-mingw32/1e360f03

P ── Loaded and on-disk path mismatch.

解决方案 #

核心问题是layout_columns()需要直接接收多个独立元素作为参数，而非打包成单个tagList传入。可以通过两种方式修复：

方案1：使用!!!拆分包列表 #

修改output$main_content部分代码：

output$main_content <- renderUI({
  req(categories())
  req(fy())
  
  cats = categories()
  cardList <- map(cats, function(cat) {
    card(card_header(cat, class = "h6 text-success"), "sample")
  })
  
  layout_columns(col_widths = rep(6, length(cats)), !!!cardList)
})

方案2：用do.call构造调用 #

output$main_content <- renderUI({
  req(categories())
  req(fy())
  
  cats = categories()
  cardList <- map(cats, function(cat) {
    card(card_header(cat, class = "h6 text-success"), "sample")
  })
  
  do.call(layout_columns, c(list(col_widths = rep(6, length(cats))), cardList))
})

两种方式都能将卡片列表拆分为独立参数传递给layout_columns，让