Customizing the Download Button Icon in Shiny Applications

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In this article, we will explore how to customize the default download button icon in a Shiny application. We’ll dive into the world of CSS and Shiny’s UI components to achieve our goal.

Understanding the Basics

Before we begin, let’s quickly review some fundamental concepts:

Shiny: A R programming language framework for building interactive web applications.
UI Components: Shiny provides a range of pre-built UI components, such as dropdownButton and downloadButton, that can be used to create user interfaces.
CSS: Cascading Style Sheets (CSS) is a styling language used to control the layout and appearance of web pages.

The Challenge

The problem we’re facing is that Shiny’s default download button icon doesn’t display our custom PNG image. We’ve tried specifying the image in the icon argument, but it didn’t work. Let’s see what’s going on under the hood.

SVG Images: A Better Alternative?

One of the answerers suggested using SVG images instead of PNGs. While we might not have explored this option yet, let’s take a closer look at why SVGs are preferred in this case:

Why SVG?

SVG (Scalable Vector Graphics) files are better suited for custom icons due to their:

Vector-based nature: SVGs use mathematical equations to draw shapes and lines, making them scalable without compromising quality.
Support for custom images: SVGs can contain external image files, such as PNGs, which allows us to reuse existing graphics.

Implementing Custom Icons

To achieve our goal of displaying a custom PNG icon, we’ll need to use CSS. Specifically, we’ll utilize the ::before pseudo-element to insert an image into our UI component.

Adding CSS

Create a new file called icon.css in your Shiny project’s www folder and add the following code:

.myicon::before {
  display: inline-block;
  line-height: 1;
  vertical-align: -.125em;
  content: url(./myicon.png);
}

In this example, replace ./myicon.png with the actual path to your custom PNG image. Make sure the file is accessible from within your Shiny application.

Updating the UI Component

Update your Shiny UI component to include a reference to the CSS file:

library(shiny)

ui <- fluidPage(
  tags$head(tags$link(href="icon.css", rel="stylesheet")),
  downloadButton(
    "dwnld",
    icon = tags$i(class = "myicon")
  )
)

Explanation

Here’s what’s happening in the updated UI component:

We add a new tags$head block to include our custom CSS file.
In the downloadButton, we specify an i element with a class of "myicon". This element will contain our custom icon.

The Finished Product

Now that we’ve customized the download button icon, let’s put everything together:

library(shiny)

ui <- fluidPage(
  tags$head(tags$link(href="icon.css", rel="stylesheet")),
  downloadButton(
    "dwnld",
    icon = tags$i(class = "myicon")
  )
)

server <- function(input, output) {
  # No server-side code required for this example
}

shinyApp(ui, server)

That’s it! With these steps, you should now be able to customize the download button icon in your Shiny application using a custom PNG image.

Conclusion

Customizing UI components can seem daunting at first, but with the right tools and knowledge, you can achieve professional-looking results. In this article, we explored how to customize the default download button icon in Shiny applications using a custom PNG image and CSS.

Last modified on 2023-11-12