cosmic_frontmatter is a package that provides a simple way to parse the frontmatter of a markdown file.

import 'package:freezed_annotation/freezed_annotation.dart';

part 'mock_frontmatter.freezed.dart';
part 'mock_frontmatter.g.dart';

@freezed
class MockFrontmatter with _$MockFrontmatter {
  const factory MockFrontmatter({
    required String title,
    required String author,
    required String excerpt,
    required String category,
    required String date,
  }) = _MockFrontmatter;

  const MockFrontmatter._();

  factory MockFrontmatter.fromJson(Map<String, dynamic> json) => _$MockFrontmatterFromJson(json);
}

const mockDocument = """
---
title: This is a test document
author: paul-halliday
excerpt: Learn how to use Markdown with Flutter at developer.school
category: Flutter
date: "2021-10-25"
---

You can learn how to use Markdown with Flutter at [developer.school](https://developer.school/tutorials/how-to-display-markdown-in-flutter).
""";

final mockFrontmatter = parseFrontmatter(
  content: mockDocument,
  frontmatterBuilder: (map) {
    // Do anything you want with the `map`:

    return MockFrontmatter.fromJson(map);
});

class _MyHomePageState extends State<MyHomePage> {
  late Document<MockFrontmatter> document;

  @override
  void initState() {
    super.initState();

    document = parseFrontmatter(
      content: mockDocument,
      frontmatterBuilder: (map) => MockFrontmatter.fromJson(map),
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(document.frontmatter.title),
      ),
      body: Padding(
        padding: const EdgeInsets.all(16.0),
        child: Center(
          child: Column(
            crossAxisAlignment: CrossAxisAlignment.stretch,
            children: [
              ListTile(
                contentPadding: EdgeInsets.zero,
                title: const Text('Title'),
                subtitle: Text(document.frontmatter.title),
              ),
              ListTile(
                contentPadding: EdgeInsets.zero,
                title: const Text('Author'),
                subtitle: Text(document.frontmatter.author),
              ),
              ListTile(
                contentPadding: EdgeInsets.zero,
                title: const Text('Excerpt'),
                subtitle: Text(document.frontmatter.excerpt),
              ),
              ListTile(
                contentPadding: EdgeInsets.zero,
                title: const Text('Category'),
                subtitle: Text(document.frontmatter.category),
              ),
              ListTile(
                contentPadding: EdgeInsets.zero,
                title: const Text('Date'),
                subtitle: Text(document.frontmatter.date),
              ),
              Text(
                'Content',
                style: Theme.of(context).textTheme.headline6,
              ),
              const SizedBox(
                height: 10,
              ),
              Expanded(
                child: MarkdownBody(
                  data: document.body,
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}