CoreTextView

Overview

iOS controls (such as UILabel and UITextView) already support NSAttributedString, but CoreTextView offers much more than simple styling. If your app needs to render both text & images, or have some custom rendering on the fly - then CoreTextView is for you.

There is another great core text library by Oliver Drobnik: DTCoreText. My goal was to create a very tiny and easy to use component (2 files only!) which is meant for simple tasks. If you really need full control of your output, I suggest to take a look at DTCoreText.

CoreTextView contains 2 major components:

• CoreTextView - UIView based, used to render the string
• HTMLParser - HTML parser which generates an instance of NSAttributedString. There is also a category for NSAttributedString, for easy creation of NSAttributedString objects.

Examples

Please also refer to the demo project for a working demo.

Basic styling

m_coreText.attributedString=[NSAttributedString attributedStringWithHTML:@"<span font='Papyrus' size='12' color='rgba(255,0,255,0.5)'>This is a styled string</span>"];

Custom Rendering

50x50 Blue circle renderer

@interface BlueCircle : NSObject<HTMLRenderer>
@end

@implementation BlueCircle
-(CGSize)size
{
	return CGSizeMake(50, 50);
}
-(void)renderInContext:(CGContextRef)context rect:(CGRect)rect
{
	CGContextSetFillColorWithColor(context, [UIColor blueColor].CGColor);
	CGContextFillEllipseInRect(context, rect);
}
@end

Using the renderer callback

NSString* html=@"DIV elements generate custom renderers: <div />";
m_coreText.attributedString=[NSAttributedString attributedStringWithHTML:html renderer:^id<HTMLRenderer>(NSMutableDictionary* attributes)
{
	return [[BlueCircle alloc] init];
}];

Styling

Since CoreTextView was designed mainly to work with custom renderers - passing attributes from the HTML to the callback should be as simple as possible. For that reason, the syntax is based on plain old HTML tags and not modern CSS. The callback receives an instance of NSMutableAttributes, which contains all available attributes of that HTML node.

The syntax was meant to be as simple as possible and at no point was it designed to follow HTML standards. For that reason, some of the HTML tags/attributes might differ from the original specs (for example, <s> for stroke rather than <stroke>)

Text

<span font='ArialMT|Georgia|noorehira|...' size='16'>Font manipulation, we can change font name and size</font>

<b>Bold>
<u style='none|single|thick|double'>Underline</u>
<i>Italic</i>
<s width='3' color='rgb(255,0,0)'>Red stroke</s>

<span align='natural|left|right|center|justified'>Aligned text</span>
<span direction='rtl|ltr'>RTL or LTR text</span>
<span wrap='word|break-word|clip|ellipsis-head|ellipsis-tail|ellipsis-middle'>Wrapped text</span>

Colors

<span color='#FF0000'>Standard HTML colors</span>
<span color='rgb(255,0,0)'>RGB color</span>
<span color='rgba(255,0,0,0.5)'>RGBA color</span>

Links

By default, all links will render using a blue color and a single underline (which you can override using the color tag and an embedded u tag). CoreTextView will try by default to open any link using [[UIApplication sharedApplication] openURL:url]. You can prevent this behaviour by returning YES from -(BOOL)coreTextView:(CoreTextView*)view openURL:(NSURL*)url delegate.

<a href='http://www.google.com/'>Google.com</a>
<a href='tel:+180012345678'>Click to call</a>

Images

Images can be embedded using the base64: prefix or be loaded from disk. Images will be loaded using [UIImage imageNamed:src] - unless the file:// scheme is specified. For images, you can also use the valign='middle' attribute to center them vertically.

<img src='base64:iVBORw0KGgoAAAANSUhEUgAAAAUAAAAFCAYAAACNbyblAAAAHElEQVQI12P4//8/w38GIAXDIBKE0DHxgljNBAAO9TXL0Y4OHwAAAABJRU5ErkJggg==' />
<img width='50' height='50' src='avatar.png' />
<img src='file://..../house.jpg' valign='middle' />

Others

<br>
<hr height='5' color='#FF0000' />

Custom Renderer

Sometimes your app needs to render some content dynamically. One option would be to generate an image and create a new NSAttributedString every time - or you can use a custom renderer.

Custom renderers use a callback, passing a graphic context to draw into. An app can then use it to draw whatever it needs.

To create a custom renderer, simply use a div tag inside your HTML. You can also set custom attributes which will be passed to the renderer factory. Custom attributes allow you to distinguish between different renderers in the same HTML.

To be able to create a custom renderer, you'll need to pass a callback to the HTML parser:

NSString* html=@"<div type='square' /><div type='circle' />";
m_coreText.attributedString=[NSAttributedString attributedStringWithHTML:html renderer:^id<HTMLRenderer>(NSMutableDictionary* attributes)
{
	if ([attributes[@"type"] isEqualToString:@"circle"])
	{
	...
	}
	return m_customRenderer;
}];

A custom renderer can be any object defining the HTMLRenderer protocol:

@protocol HTMLRenderer<NSObject>
@required
@property(nonatomic,readonly) CGSize size;
@optional
@property(nonatomic,readonly) CGFloat ascent;
@property(nonatomic,readonly) CGFloat descent;

@required
-(void)renderInContext:(CGContextRef)context rect:(CGRect)rect;
@end

The only 2 required methods are -(CGSize>size and -(void)renderInContext:(CGContextRef)context rect:(CGRect)rect, so if we want to draw a simple blue circle, our renderer will be similar to the following implementation:

@interface BlueCircle : NSObject<HTMLRenderer>
@end
@implementation BlueCircle
-(CGSize)size
{
	return CGSizeMake(50, 50);	// make our circle 50x50 points
}
-(void)renderInContext:(CGContextRef)context rect:(CGRect)rect
{
	CGContextSetFillColorWithColor(context, [UIColor blueColor].CGColor);
	CGContextFillEllipseInRect(context, rect);
}
@end

We then use the parser's factory callback to create a new instance of BlueCircle. The new renderer will be retained by the resulting NSAttributedString.

m_coreText.attributedString=[NSAttributedString attributedStringWithHTML:@"Hello <div /> World" renderer:^id<HTMLRenderer>(NSMutableDictionary* attributes)
{
	return [[BlueCircle alloc] init];
}];

Setup

Everything is contained in 2 files only: CoreTextView.mm & CoreTextView.h.

CoreTextView uses ARC. If your project does not use ARC, you'll need to set the following flag for CoreTextView.mm: -fobjc-arc (How to enable ARC for a single file)

You'll also need to include libxml2.dylib in your project:

• Link your project against libxml2.dylib and CoreText.framework
• Under your build settings, add the following path under "Header Search Paths": /usr/include/libxml2

Credits

CoreTextView was created by Gilad Novik

Many thanks for Oliver Drobnik and his amazing work with DTCoreText.

License

CoreTextView is licensed under zlib license:

Copyright (c) 2013 Gilad Novik

This software is provided 'as-is', without any express or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software.

Permission is granted to anyone to use this software for any purpose, including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions:

1. The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required.

2. Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software.

3. This notice may not be removed or altered from any source distribution.

You do not have to mention CoreTextView in your app, but I'll appreciate if you do so anyway (or at least email me to let me know about your new great app :-) )

Usage

Use it, fork it, push updates - enjoy it!