如何在bslib::card_header中添加小图标版shiny::downloadButton？

可以通过以下几种方法调整图标尺寸，避免卡片头部高度异常：

方案1：直接调整downloadButton的图标与按钮样式 #

给downloadButton添加内联样式控制图标大小，同时通过align-items-center让标题与按钮垂直居中：

bslib::card_header(
    class = "d-flex justify-content-between align-items-center",
    "Card Title",
    shiny::downloadButton(
        outputId="download",
        label="",
        icon=shiny::icon("image"),
        style = "font-size: 1.2rem; padding: 0.25rem 0.5rem;"
    )
)

方案2：用downloadLink配合自定义按钮样式 #

downloadLink虽无直接的icon参数，但可以嵌套图标标签，并通过bootstrap按钮类控制尺寸：

bslib::card_header(
    class = "d-flex justify-content-between align-items-center",
    "Card Title",
    shiny::tags$a(
        id = "download",
        class = "btn btn-outline-primary btn-sm",
        shiny::icon("image", style = "font-size: 1rem;"),
        href = "",
        target = "_blank",
        download = NA
    )
)

方案3：使用bslib自带的download_button（最适配） #

bslib的download_button支持size参数直接控制按钮与图标尺寸，完美适配bslib主题：

bslib::card_header(
    class = "d-flex justify-content-between align-items-center",
    "Card Title",
    bslib::download_button(
        outputId="download",
        label="",
        icon=shiny::icon("image"),
        size = "sm"
    )
)

完整示例代码（方案3） #

require(shiny)
require(bslib)
require(ggplot2)

ui <- bslib::page_fillable(
    theme=bslib::bs_theme(version=5),
    title = "Card with Download Icon",
    bslib::card(
        bslib::card_header(
            class = "d-flex justify-content-between align-items-center",
            "Card Title",
            bslib::download_button(
                outputId="download",
                label="",
                icon=shiny::icon("image"),
                size = "sm"
            )
        ),
        shiny::plotOutput("the_plot")
    )
)

server <- function(input, output, session) {
    plot_obj <- shiny::reactive(
        ggplot2::qplot(Sepal.Length, Sepal.Width, data = iris)
    )
    output$the_plot <- shiny::renderPlot(plot_obj())
    output$download <- shiny::downloadHandler(
        filename = function() "card_snapshot.png",
        content = function(file) {
            ggplot2::ggsave(
                filename=file, plot=plot_obj(), device=png,
                width=16, height=9, units="cm", bg="white"
            )
        }
    )
}

shiny::shinyApp(ui, server)

内容的提问来源于stack exchange，提问作者Karsten W.