MarkdownView (Fork)

A powerful pure UIKit framework for rendering Markdown documents with real-time parsing and rendering capabilities. Battle tested in FlowDown.

This is a fork of Lakr233/MarkdownView with enhancements for Open UI, an iOS client for Open WebUI.

Fork Changes

🔗 Clickable Links

• Links are now tappable out of the box — a default linkHandler opens URLs in Safari via UIApplication.shared.open(url)
• No additional configuration needed; works automatically in SwiftUI via MarkdownView("text")

🎨 HighlightSwift (Replaces Highlightr)

• Swapped Highlightr (Obj-C JSContext) → HighlightSwift (pure Swift JavaScriptCore)
• Lazy async per-block highlighting: Code blocks render plain monospaced text immediately, then highlight asynchronously with a 300ms debounce — no color flickering during streaming
• Dark mode: .dark(.github) theme with automatic light/dark switching
• LRU cache: Highlighted results are cached to avoid re-highlighting on scroll

📐 Configurable Spacing

• Paragraph spacing, line spacing, heading spacing, blockquote spacing, and blockquote indent are now configurable via theme.spacings (previously hardcoded to 16/4)
• List spacing follows theme settings

📝 Improved List Rendering

• Plain numbered lists: Replaced circled emoji numbers (①②③) with plain 1. 2. 3. CoreText rendering via CTLineDraw
• Dynamic indent: Measures max number width in a list and uses that + padding as the base indent — scales correctly for any list size
• Left-aligned numbers: Fixed position like bullet points for consistent alignment

✏️ Italic Emphasis

• Changed emphasis rendering from underline to italic font (matches standard markdown conventions)

🔧 Code Block Height Fix

• Code blocks use actual intrinsicContentSize instead of a formula-based height calculation — fixes extra bottom whitespace

⚡ Streaming Performance — Block-Level Incremental Rendering

Major rendering pipeline overhaul to keep 120Hz ProMotion smooth during long AI streaming sessions:

• Block-level render cache (CachedBlockSegment): Each MarkdownBlockNode is rendered once and cached. On every streaming update, only the blocks that actually changed are re-rendered — unchanged blocks (the entire clean prefix of the document) are reused at zero cost.
• Persistent NSMutableAttributedString mutation: Instead of rebuilding the full concatenated attributed string on every token (O(n_total)), the dirty tail is deleted and replaced in-place (O(n_dirty)). CoreText only re-lays out the portion that changed.
• Deferred layout: Removed the synchronous layoutIfNeeded() call after every streaming update. setNeedsLayout() is used instead, letting the run loop coalesce and batch layout passes — prevents main-thread stalls on large documents.
• Throttled height measurement: boundingSize(for:) / intrinsicContentSize (a full O(n) CoreText layout pass) is throttled to at most once per 150ms during streaming. Immediately measured when streaming ends or content changes.
• buildSingleBlock: New TextBuilder.buildSingleBlock(node:view:viewProvider:) method that renders a single MarkdownBlockNode in isolation, enabling the incremental path without a full document rebuild.

Features

• 🚀 Real-time Rendering: Live Markdown parsing and rendering as you type
• 🖥️ Specialized for Mobile Display: Optimized layout that extracts complex elements from lists for better readability
• 🎨 Syntax Highlighting: Beautiful code syntax highlighting with HighlightSwift
• 📊 Math Rendering: LaTeX math formula rendering with SwiftMath
• 📱 Cross-Platform: Native support for iOS, macOS, Mac Catalyst, and visionOS
• 🔗 Clickable Links: Links open in Safari automatically — no setup required

Installation

Add the following to your Package.swift file:

dependencies: [
    .package(url: "https://github.com/Ichigo3766/MarkdownView", branch: "main"),
]

Platform compatibility:

• iOS 16.0+
• macOS 13.0+
• Mac Catalyst 16.0+
• visionOS 1.0+

Usage

SwiftUI

import MarkdownView

struct ContentView: View {
    var body: some View {
        MarkdownView("# Hello World\n\nLinks are [clickable](https://example.com) by default!")
    }
}

With custom theme:

MarkdownView("# Hello World", theme: .default)

UIKit / AppKit

import MarkdownView
import MarkdownParser

let markdownTextView = MarkdownTextView()
let parser = MarkdownParser()
let result = parser.parse("# Hello World")
let content = MarkdownTextView.PreprocessedContent(parserResult: result, theme: .default)
markdownTextView.setMarkdown(content)

// Links are clickable by default, or set a custom handler:
markdownTextView.linkHandler = { payload, range, point in
    switch payload {
    case .url(let url): UIApplication.shared.open(url)
    case .string(let str): if let url = URL(string: str) { UIApplication.shared.open(url) }
    }
}

Example

Check out the included example project to see MarkdownView in action:

cd Example
open Example.xcodeproj

License

This project is licensed under the MIT License. See the LICENSE file for details.

Acknowledgments

• Original framework by Lakr233
• Code adapted from swift-markdown-ui by Guillermo Gonzalez, used under the MIT License.

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Copyright 2025 © Lakr Aream. All rights reserved.