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stevengharris/MarkupEditor 0.3.2
WYSIWYG editing for SwiftUI and UIKit apps
⭐️ 74
🕓 1 week ago
iOS macOS
.package(url: "https://github.com/stevengharris/MarkupEditor.git", from: "0.3.2")

iOS 14.5+ MacOS 11.3+ Twitter: @stevengharris


WYSIWYG editing for SwiftUI and UIKit apps.

Jealous of those JavaScript coders with their WYSIWYG text editors, but just can't stomach the idea of immersing yourself in JavaScript when you're enjoying the comfort and joy of Swift? Yeah, me too. So when I was forced to do it, I thought I'd share what I did as a way to help others avoid it.



MarkupEditor Goals and Non-Goals

I am working on a larger project that requires embedded support for "rich text" editing. WYSIWYG editing is a must-have requirement for me. I could have forced my developer-users to use Markdown, but I find it to be annoying both to write and to look at while writing. Who wants to have to mentally filter all that cruft on the screen? Sure, it's a lot better than editing raw HTML; but come on, this is the 21st century. Having to deal with an editing experience where you use some kind of "preview mode" to make sure that what you are writing will be presented like you expect feels like CI/CD for writing.

Still, I wanted an editing experience that didn't get in the way. I wanted something with the feature-simplicity of Markdown, but presented in a clean, what-you-see-is-what-you-get manner that supported the basics people expect:

  1. Styling
    • Present a paragraph or header with a predefined font size
    • Bulleted and numbered lists
    • Indenting and outdenting of text
  2. Formatting
    • Bold, italic, underline, code, strikethrough, sub- and super-scripting
  3. Embedding
    • Images
    • Tables
    • Links

As you might expect, then, this feature set is pretty darned close to Markdown - or at least a GitHub flavor of Markdown. And as soon as you do WYSIWYG editing, you must support undo/redo properly. The feature list doesn't include some things you might expect from your favorite word processor:

  • Colored text
  • Highlighting
  • Font size changes (except as implied by identifying something as a paragraph or header)

The initial open source release does not support the following (but I plan to):

  • Text alignment (although how well this translates back-and-forth to Markdown remains to be seen)
  • Flexible table formatting
  • Copy/paste preserving formatting (currently only supports plain text)

If you want a richer feature set, you can extend the MarkupEditor yourself. The demos include examples of how to extend the MarkupEditor's core features and how to interact with the file system for saving what you edit. It's my intent to keep the core MarkupEditor feature set to be similar to what you will see in GitHub Markdown.

What is WYSIWYG, Really?

The MarkupEditor is presenting an HTML document to you as you edit. It uses JavaScript to change the underlying DOM and calls back into Swift as you interact with the document. The MarkupEditor does not know how to save your document or transform it to some other format. This is something your application that consumes the MarkupEditor will need to do. The MarkupEditor will let your MarkupDelegate know as the underlying document changes state, and you can take advantage of those notifications to save and potentially transform the HTML into another form. If you're going to do that, then you should make sure that round-tripping back into HTML also works flawlessly. Otherwise, you are using a "What You See Is Not What You Get" editor, which is both less pronounceable and much less useful to your end users.

Consuming the MarkupEditor

Behind the scenes, the MarkupEditor interacts with an HTML document (created in markup.html) that uses a single contentEditable DIV element to modify the DOM of the document you are editing. It uses a subclass of WKWebView - the MarkupWKWebView - to make calls to the JavaScript in markup.js. In turn, the JavaScript calls back into Swift to let the Swift side know that changes occurred. The callbacks on the Swift side are handled by the MarkupCoordinator. The MarkupCoordinator is the WKScriptMessageHandler for a single MarkupWKWebView and receives all the JavaScript callbacks in userContentController(_:didReceive:). The MarkupCoordinator in turn notifies your MarkupDelegate of changes. See MarkupDelegate.swift for the full protocol and default implementations.

That sounds complicated, but it is mostly implementation details you should not need to worry about. The MarkupDelegate protocol is the key mechanism for your app to find out about changes as the user interacts with the document. The MarkupWKWebView is the key mechanism to make changes to the document from the Swift side or to obtain information from the document, such as its contents. The MarkupToolbar is a convenient, pre-built UI to invoke changes to the document by interacting with the MarkupWKWebView.

To avoid spurious logging from the underlying WKWebView in the Xcode console, you can set OS_ACTIVITY_MODE to disable in the Run properties for your target.

NOTE: The MarkupEditor at this point has only really been used as a Mac Catalyst app and has some implicit dependencies on using it with a keyboard.

Swift Package

Add the MarkupEditor package to your Xcode project using File -> Swift Packages -> Add Package Dependency...


Clone this repository and build the MarkupFramework target in Xcode. Add the MarkupEditor.framework as a dependency to your project.

SwiftUI Usage

When consuming the MarkupEditor in SwiftUI, you can use the MarkupToolbar and MarkupWebView directly in your own View. The MarkupWebView is a UIViewRepresentable for the MarkupWKWebView and deals with setting up the MarkupCoordinator itself.

In the simplest case, just add the MarkupToolbar and a MarkupWebView to your ContentView. We let the transient SubToolbar (used to create and edit images, links, and tables) be an overlay of MarkupWebView. The selectedWebView has to be accessed by both the MarkupToolbar and MarkupWebView, and is accessible via the MarkupEnv. By setting your ContentView as the markupDelegate, it will receive the markupDidLoad callback when a MarkupWKWebView has loaded its content along with the JavaScript held in markup.js. (If you have multiple MarkupWebViews and a single MarkupToolbar, you can use the markupTookFocus callback to tell the MarkupToolbar which view it should operate on.) The example below shows how to use the markupDidLoad callback to assign the selectedWebView so that the MarkupToolbar correctly reflects the selectionState as the user edits and positions the caret in the document.

import SwiftUI
import MarkupEditor

struct ContentView: View {
    private let markupEnv = MarkupEnv(style: .compact)
    private let showSubToolbar = ShowSubToolbar()
    private var selectedWebView: MarkupWKWebView? { markupEnv.observedWebView.selectedWebView }
    @State private var demoContent: String = "<p>Hello world</p>"
    var body: some View {
        VStack(spacing: 0) {
            MarkupToolbar(markupDelegate: self)
                .padding(EdgeInsets(top: 2, leading: 8, bottom: 2, trailing: 8))
            MarkupWebView(markupDelegate: self, boundContent: $demoContent)
                    SubToolbar(markupDelegate: self),
                    alignment: .topLeading)

extension ContentView: MarkupDelegate {
    func markupDidLoad(_ view: MarkupWKWebView, handler: (()->Void)?) {
        markupEnv.observedWebView.selectedWebView = view

UIKit Usage

The MarkupToolbar is a SwiftUI View, so consuming it in UIKit is a bit more complicated than in SwiftUI. You also need to create and hook up the MarkupCoordinator yourself, something that is done by the SwiftUI MarkupWebView. Please refer to the UIKitDemo code for a detailed example. I'd like there to be less boilerplate code, but I'm also planning on using the MarkupEditor in a SwiftUI app so am likely not to put a lot of effort into that.

Local Images

Being able to insert an image into a document you are editing is fundamental. In Markdown, you do this by referencing a URL, and the URL can point to a file on your local file system. The MarkupEditor can do the same, of course, but when you insert an image into a document in even the simplest WYSIWYG editor, you don't normally have to think, "Hmm, I'll have to remember to copy this file around with my document when I move my document" or "Hmm, where can I stash this image so it will be accessible across the Internet in the future." From an end-user perspective, the image is just part of the document. Furthermore, you expect to be able to paste images into your document that you copied from elsewhere. Nobody wants to think about creating and tracking a local file in that case.

The MarkUpEditor refers to these images as "local images", in contrast to images that reside external to the document. Both can be useful! When you insert a local image (by selecting it from the Image Toolbar or by pasting it into the document), the MarkupEditor creates a new image file using a UUID for the file name. By default, that file resides in the same location as the text you are editing. For the demos, the document HTML and local image files are held in an id subdirectory of the URL found from FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask). You can pass the id to your MarkupWKWebView when you create it - for example, it might be the name of the document you're editing. When the MarkupEditor creates a new local image file, your MarkupDelegate receives a notification via the markupImageAdded(url: URL) method, giving you the URL of the new local image.

Although local image support was a must-have in my case, it seems likely some MarkupEditor consumers would feel like it's overkill our would like to preclude its use. For this reason, there is a ToolbarPreference to control whether to allow selection of images from local files. Local images are disallowed by default. To enable them, specify allowLocalImages when you create the MarkupEnv, like MarkupEnv(style: .compact, allowLocalImages: true). This will add a Select button to the Image Toolbar.

A reminder: The MarkupEditor does not know how/where you want to save the document you're editing or the images you have added locally. This is the responsibility of your app.


There are three test targets: BasicTests, UndoTests, and RedoTests. Proper undo and redo has been one of the more challenging parts of the project. Essentially, every time the MarkupEditor implements changes to the underlying DOM, it also has to support undoing and redoing those changes. (As a historical aside, the MarkupEditor does not use the deprecated HTML document.execCommand, except in a very limited way. The execCommand takes care of undo and redo for anything you use it for. For example, if you use document.execCommand('bold') to bold the document selection, undo and redo "just work", albeit leaving behind various spans and styles in their wake. Because the MarkupEditor doesn't use execCommand, the undo and redo logic for every operation supported by the MarkupEditor has been hand-crafted with a mixture of love, frustration, and occasional anger.)

The BasicTests target tests the "do" operations; i.e., the operations you can perform via the MarkupWKWebView API or one of the toolbars. The UndoTests do all the "do" operations of the BasicTests, plus the "undo" of each one to make sure the original HTML is restored. The RedoTests do all the "do" and "undo" operations, plus the "redo" of each one to make sure the results of the original "undo" are restored. As a result, running just the RedoTests will also do the equivalent of the UndoTests, and running UndoTests will also do the the equivalent of running BasicTests. The RedoTests take a while to run and can be considered to be a comprehensive run through the MarkupEditor functionality.


If you consume just the package, you don't get the demo targets to build. If you create a workspace that contains the MarkupEditor project or just clone this repository, you will also get the two demo targets, creatively named SwiftUIDemo and UIKitDemo. There is also a MarkupEditor framework target in the project that is 100% the equivalent of the Swift package. By default, the demos both consume the framework, because I find it to be a lot less hassle when developing the project overall, especially in the early stage. The only difference between consuming the framework and the Swift package is how the MarkupWKWebView locates and loads its markup.html resource when it is instantiated. The demos have a dependency on the MarkupEditor.framework.

The demos open demo.html, which contains information about how to use the MarkupEditor as an end user and shows you the capabilities.


The current version is closing in on feature-complete. I am now consuming it myself in another project I am developing, so changes are being driven primarily by MarkupEditor uptake in that project (and any issues people might raise).


Version 0.3.1

This version is getting closer feature-complete on Mac Catalyst. There have been some API changes from the 0.2 version, primarily driven by the new support for local images.

  • Support local images in the edited document, the ability to insert an image from file as opposed to an external URL.
  • Refactor tests into BasicTests, UndoTests, and RedoTests. Tests have no dependency on a host app.
  • All operations support undo/redo properly (with the exception of selections across paragraphs, as cited in Known Issues).
  • Support pasting HTML and images. (Previously only plain text was supported.)
  • Menus work in the demos but are still incomplete.
  • List editing responds properly to the Enter key at beginning, inside, and end of list items. Enter in an empty list item outdents until exiting the list.
  • Tab is now strictly a table navigation mechanism and is no longer associated with indent/outdent operations.

Version 0.2.2

The labeled toolbar took up too much screen real estate in my other project, so I created a .compact form and made that selectable via ToolbarPreference. Now I have a way to add other preferences easily. I also needed a better way to communicate the selectionState and selectedWebView when I have an arbitrary number of MarkupWebViews being editing using a single MarkupToolbar. I set up MarkupEnv to accomplish that and adjusted the SwiftUIDemo and UIKitDemo to use it.

  • Add this History section to the README.
  • Make the toolbar configurable between .compact (the new default) and .labeled via ToolbarPreference.
  • Use MarkupEnv to access the selectionState and selectedWebView.
  • Bundle loading logic now depends on SWIFT_PACKAGE in MarkupWKWebView, not my homegrown USEFRAMEWORK setting.
  • Some minor adjustments to backgrounds and css to fix issues when the MarkupToolbar and MarkupWebView were embedded in other SwiftUI views.

Version 0.2.1

  • This was the first version made public and open sourced.

Known Issues

  1. At this point, the MarkupEditor is really only useful on devices with a keyboard. On the iPad (and worse on the iPhone), the toolbar is too wide, and it isn't set up for scrolling or, better, for a different display for the format. I intend to work on the iPad usage but have not put any time into it. I am primarily focused on using it on the Mac.
  2. Table editing
    • Table styling is hardcoded. I plan to provide options for putting borders around elements, header, etc.
    • Headers are currently colspanning the full table, but this needs to be adjustable.
  3. Image editing
    • Selection is funky. Should show the image itself being selected but does not.
    • Scaling is clunky. I plan to replace the Stepper with an overlay with handles on the image.
    • Save and cancel should go away in favor of immediate preview and undo.
    • The UI to deal with local images vs external image references is rough.
  4. Multi-element selections are a work in progress. For example, selecting multiple paragraphs and changing their style works, but undo/redo of the same does not. Operations performed for selections across lists and tables will result in unpredicatable behavior and attempts to undo may make things worse.
  5. Pasting of text with embedded HTML causes weird things to happen since the embedded HTML is not properly sanitized yet.


  1. Probably needs to support text justification, but I may not do so.
  2. Preferences. Some things are properly configurable via ToolbarPreferences, but this needs to be expanded.
  3. Menus are incomplete, but the scaffolding is in place to be filled-out.

Legacy and Acknowledgements

When I started my search for an open source "Swift WYSIWYG editor", I found a kind of mishmash of things. The RichEditorView was one of the most visible. The RichEditorView was originally built using UIWebView, which has long been deprecated. A couple of people forked and ported it to WKWebView and shared their work. I used that for a while in some work I was doing, but I kept hitting edges and felt like I was having to put a lot of work into a fork that would never really see the light of day. The thought of moving the result into SwiftUI was making me queasy. The MarkupEditor is meant to be a proper "modern" version for WYSIWYG editing you can use in your SwiftUI or UIKit project, but it was hatched in the original RichEditorView.

The MarkupEditor's approach of using an HTML document containing a contentEditable DIV under the covers seems like a good idea until you read Nick Santos' article about Why ContentEditable is Terrible. His main arguments center around WYSIWYG, and the meaning of the term when editing a document in this way. In the simplest case, consider if you save the HTML you edited using the MarkupEditor and then use a different CSS to display it in a different browser. What you saw when you edited will certainly not be what you get. The text content will be 100% the same, of course. If what you are editing and saving remains in the same HTML form and is presented using the same CSS using a WKWebView, then it will be WYSIWYG. In any case, you need to think about it when adopting this approach.

The MarkupEditor has the advantage of not supporting arbitrary HTML, and in fact, owns the definition of the exact subset of HTML that is allowed. It is targeted only at WKWebView, so there are no browser portability problems. The restrictions on functionality and the absence of styling elements from the HTML help avoid some of the problems cited in his article. Also, by avoiding use of (the now deprecated but likely to live forever) Document.execCommand to perform editing tasks against the DOM, the MarkupEditor avoids WebKit polluting the "clean" HTML with spans and styles.

In case you think "To heck with this contentEditable nonsense. How hard can it be to build a little editor!?", I refer you to this article on lord.io. I did not enjoy writing JavaScript while implementing this project, but the DOM and its incredibly well-documented API are proven and kind of amazing. To be able to ride on top of the work done in the browser is a gift horse that should not be looked in the mouth.


The alert sound used in the demos was obtained from freesound.org. It was created by rhodesmas and provided under the Creative Commons Attribution License.


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