flutter_markdown

Flutter Markdown

A markdown renderer for Flutter. It supports the original format, but no inline HTML.

Overview

The flutter_markdown package renders Markdown, a lightweight markup language, into a Flutter widget containing a rich text representation.

flutter_markdown is built on top of the Dart markdown package, which parses the Markdown into an abstract syntax tree (AST). The nodes of the AST are an HTML representation of the Markdown data.

Flutter Isn't an HTML Renderer

While this approach to creating a rich text representation of Markdown source text in Flutter works well, Flutter isn't an HTML renderer like a web browser. Markdown was developed by John Gruber in 2004 to allow users to turn readable, plain text content into rich text HTML. This close association with HTML allows for the injection of HTML into the Markdown source data. Markdown parsers generally ignore hand-tuned HTML and pass it through to be included in the generated HTML. This trick has allowed users to perform some customization or tweaking of the HTML output. A common HTML tweak is to insert HTML line-break elements <br /> in Markdown source to force additional line breaks not supported by the Markdown syntax. This HTML trick doesn't apply to Flutter. The flutter_markdown package doesn't support inline HTML.

Markdown Specifications and flutter_markdown Compliance

There are three seminal documents regarding Markdown syntax; the original Markdown syntax documentation specified by John Gruber, the CommonMark specification, and the GitHub Flavored Markdown specification.

The CommonMark specification brings order to and clarifies the Markdown syntax cases left ambiguous or unclear in the Gruber document. GitHub Flavored Markdown (GFM) is a strict superset of CommonMark used by GitHub.

The markdown package, and in extension, the flutter_markdown package, supports four levels of Markdown syntax; basic, CommonMark, GitHub Flavored, and GitHub Web. Basic, CommonMark, and GitHub Flavored adhere to the three Markdown documents, respectively. GitHub Web adds header ID and emoji support. The flutter_markdown package defaults to GitHub Flavored Markdown.

Getting Started

Using the Markdown widget is simple, just pass in the source markdown as a string:

const Markdown(data: markdownSource);

If you do not want the padding or scrolling behavior, use the MarkdownBody instead:

const MarkdownBody(data: markdownSource);

By default, Markdown uses the formatting from the current material design theme, but it's possible to create your own custom styling. Use the MarkdownStyle class to pass in your own style. If you don't want to use Markdown outside of material design, use the MarkdownRaw class.

Selection

By default, Markdown is not selectable. A caller may use the following ways to customize the selection behavior of Markdown:

• Set selectable to true, and use onTapText and onSelectionChanged to handle tapping and selecting events.
• Set selectable to false, and wrap Markdown with SelectionArea or SelectionRegion.

Emoji Support

Emoji glyphs can be included in the formatted text displayed by the Markdown widget by either inserting the emoji glyph directly or using the inline emoji tag syntax in the source Markdown document.

Markdown documents using UTF-8 encoding can insert emojis, symbols, and other Unicode characters directly in the source document. Emoji glyphs inserted directly in the Markdown source data are treated as text and preserved in the formatted output of the Markdown widget. For example, in the following Markdown widget constructor, a text string with a smiley face emoji is passed in as the source Markdown data.

Markdown(
  controller: controller,
  selectable: true,
  data: 'Insert emoji here😀 ',
);

The resulting Markdown widget will contain a single line of text with the emoji preserved in the formatted text output.

The second method for including emoji glyphs is to provide the Markdown widget with a syntax extension for inline emoji tags. The Markdown package includes a syntax extension for emojis, EmojiSyntax. The default extension set used by the Markdown widget is the GitHub flavored extension set. This pre-defined extension set approximates the GitHub supported Markdown tags, providing syntax handlers for fenced code blocks, tables, auto-links, and strike-through. To include the inline emoji tag syntax while maintaining the default GitHub flavored Markdown behavior, define an extension set that combines EmojiSyntax with ExtensionSet.gitHubFlavored.

import 'package:markdown/markdown.dart' as md;
// ···
  Markdown(
    controller: controller,
    selectable: true,
    data: 'Insert emoji :smiley: here',
    extensionSet: md.ExtensionSet(
      md.ExtensionSet.gitHubFlavored.blockSyntaxes,
      <md.InlineSyntax>[
        md.EmojiSyntax(),
        ...md.ExtensionSet.gitHubFlavored.inlineSyntaxes
      ],
    ),
  );

Image Support

The Img tag only supports the following image locations:

• From the network: Use a URL prefixed by either http:// or https://.

• From local files on the device: Use an absolute path to the file, for example by concatenating the file name with the path returned by a known storage location, such as those provided by the path_provider plugin.

• From image locations referring to bundled assets: Use an asset name prefixed by resource:. like resource:assets/image.png.

Verifying Markdown Behavior

Verifying Markdown behavior in other applications can often be useful to track down or identify unexpected output from the flutter_markdown package. Two valuable resources are the Dart Markdown Live Editor and the Markdown Live Preview. These two resources are dynamic, online Markdown viewers.

Markdown Resources

Here are some additional Markdown syntax resources:

• Markdown Guide
• CommonMark Markdown Reference
• GitHub Guides - Mastering Markdown
  • Download PDF cheatsheet version