DTCoreText

This project aims to duplicate the methods present on Mac OSX which allow creation of NSAttributedString from HTML code on iOS. Previously we referred to it as NSAttributedString+HTML (or NSAS+HTML in short) but this only covers about half of what this framework does.

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The project covers two broad areas:

Layouting - Interfacing with CoreText, generating NSAttributedString instances from HTML code
UI - several UI-related classes render these objects

This is useful for drawing simple rich text like any HTML document without having to use a UIWebView.

Please read the Q&A.

Your help is much appreciated. Please send pull requests for useful additions you make or ask me what work is required.

If you find brief test cases where the created NSAttributedString differs from the version on OSX please send them to us!

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License

It is open source and covered by a standard BSD license. That means you have to mention Cocoanetics as the original author of this code. You can purchase a Non-Attribution-License from us.

Documentation

Documentation can be browsed online or installed in your Xcode Organizer via the Atom Feed URL.

Requirements

DTCoreText needs a minimum iOS deployment target of iOS 4.2 because of:

NSCache
GCD-based threading and locking
Blocks
ARC

DTCoreText is designed to be included as static library from a subproject, it embeds several classes from the DTFoundation project. If you want to use DTFoundation as well in your project you need to use the "Static Library (no DTFoundation)" target to avoid duplicate symbols.

Setup

The best way to use DTCoreText is to add it in Xcode as a subproject of your project with the following steps.

Make DTCoreText a git submodule of your project

git submodule add https://github.com/Cocoanetics/DTCoreText.git Externals/DTCoreText
DTCoreText uses DTHTMLParser and DTVersion from DTFoundation which is set up as a git submodule in Core/Externals/DTFoundation, so you need to get these files as well

git submodule update --init --recursive
Open the destination project and create an "Externals" group.
Add files… or drag DTCoreText.xcodeproj to the Externals group
In your application target's Build Phases: Target Dependencies add the Static Library from the DTCoreText sub project

In your application target's Build Phases: Link Binary With Libraries phase add the following:

 libDTCoreText.a (target from the DTCoreText sub-project)
 libxml2.dylib
 ImageIO.framework
 QuartzCore.framework
 CoreText.framework
 MobileCoreServices.framework

Go to File: Project Settings… and change the derived data location to project-relative.
Add the DerivedData folder to your git ignore.
In your application's target Build Settings:
- Add $(PROJECT_DIR) to User Header Search Paths, set to recursive
- Set Always Search User Paths to Yes.
- Add the -ObjC flag to your app target's Other Linker Flags

OPTIONAL LINKER SETTINGS:

If you find that your app crashes with an unrecognized selector from one of this library's categories, you might also need the -all_load linker flag. Alternatively you can use -force-load with the full path to the static library. This causes the linker to load all categories from the static library.
If your app does not use ARC yet (but DTCoreText does) then you also need the -fobjc-arc linker flag.

Known Issues

CoreText has a problem prior to iOS 5 where it takes around a second on device to initialize its internal font lookup table. You have two workarounds available:

trigger the loading on a background thread like shown in http://www.cocoanetics.com/2011/04/coretext-loading-performance/
if you only use certain fonts then add the variants to the DTCoreTextFontOverrides.plist, this speeds up the finding of a specific font face from the font family

Some combinations of fonts and unusual list types cause an extra space to appear. e.g. 20 px Courier + Circle

In many aspects DTCoreText is superior to the Mac version of generating NSAttributedStrings from HTML. These become apparent in the MacUnitTest where the output from both is directly compared. I am summarizing them here for references.

In the following "Mac" means the initWithHTML: methods there, "DTCoreText" means DTCoreText's initWithHTML and/or DTHTMLAttributedStringBuilder.

Mac does not support the video tag, DTCoreText does.
DTCoreText is able to synthesize small caps by putting all characters in upper case and using a second smaller font for lowercase characters.
I suspect that Mac makes use of the -webkit-margin-* CSS styles for spacing the paragraphs, DTCoreText only uses the -webkit-margin-bottom and margin-bottom at present.
Mac supports CSS following addresses, e.g. "ul ul" to change the list style for stacked lists. DTCoreText does not support that and so list bullets stay the same for multiple levels.
Mac outputs newlines in PRE tags as \n, iOS replaces these with Unicode Line Feed characters so that the paragraph spacing is applied at the end of the PRE tag, not after each line. (iOS wraps code lines when layouting)
Mac does not properly encode a double list start. iOS prints the empty list prefix.
Mac seems to ignore list-style-position:outside, iOS does the right thing.