Update: The work with a new and improved version of InterfaCSS is underway in the develop branch... 😁 The latest version (Beta2) adds support for XML-based layout using Flexbox (powered by Facebook Yoga)!

Everyone loves a beautifully designed app with a consistent UI, and getting there shouldn't take a huge effort. What if there was a way to do styling, theming and layout in a concise and powerful way, without constantly having to repeat yourself. What if things could be more like the web?

Welcome to InterfaCSS

Simple yet powerful styling

InterfaCSS uses an easy to understand styling syntax that is based on the the familiar CSS styling language used on the web (augmented with some Sass/Less-like features, such as nested declarations and variables), which means that you (and your designer) will probably feel right at home. InterfaCSS supports a rich selector syntax (type, class and element id selectors, selector combinators, pseudo classes, etc) and property names are what you expect them to be - i.e. the same as in UIKit, and you can set things like fonts, colors, images, transform, insets, offsets, rects, enums and much, much more.

#helloWorldButton {
  attributedText: "Hello " (foregroundColor: yellow), "World" (foregroundColor: #0000ff);
  backgroundColor: "patternImageAsColor.png";
  borderWidth: 3;
  borderColor: fadeout(magenta, 75%);
  cornerRadius: @numberVariable;
  clipsToBounds: YES;
  layout: size(100, 21), left(parent + 10), top(guide.top + 100);
  transform: rotate(15);
}

InterfaCSS can get you DRY

We all hate to duplicate code, so why should styling be any different? Sure, UIAppearance provides some help, but would you still want to write (and read) things like this:

[[UIButton appearanceWhenContainedIn:UITableViewCell.class, nil] setTitleColor:
    [UIColor colorWithRed:255 green:109 blue:16 alpha:1] forState:UIControlStateSelected];

when you instead can write it like this:

UITableViewCell UIButton {
    titleColor(selected): #ff6d10;
}

/* Or what if you actually needed a bit more fine-grained control: */
BraveNewViewController UITableViewCell UIButton.mySpecialButton {
    titleColor(selected): #ff6d10;
}

Flexible layouts, the easy way

InterfaCSS lets you define layouts based on values that depend on the position and size of other elements. Layouts are expressed directly in the stylesheet file, and the format is very easy to understand.

#view1 {
    layout: size(25, 25), left(parent.leftMargin), top(parent.topMargin);
}

#view2 {
    layout: size(view1, view1), left(view1.right + 10), top(view1.top);
}

In addition, using a view builder, setting up the UI in your view controllers is a breeze - gone are the days of writing tedious UI setup code or fiddling with unwieldy xib-files (but you can still use them just fine with InterfaCSS if you want of course) - simply define your UI in an XML file or do it in code, by using ISSViewBuilder.

XML:

<view id="rootView">
    <view id="view1"/>
    <view id="view2" layout="size(view1, view1), left(view1.right + 10), top(view1.top)"/> <!-- It's possible to define layouts here as well -->
</view>

In code (Swift):

self.view = ISSViewBuilder.rootViewWithId("rootView", withOwner: self, andSubViews: {
    return [
        ISSViewBuilder.viewWithId("view1"),
        ISSViewBuilder.viewWithId("view2"),
    ];
})

Style as you go

Styling isn't something you just do at startup of course - you can easily modify the styling any time by using methods defined in the category UIView+InterfaCSS.h, for example:

self.view.styleClassISS = @"groovyStyle anotherGroovyStyle"; // Supports multiple style classes separated by whitespace - TIP: This property is also IBInspectable

self.view.elementIdISS = @"groovyElement"; // To uniquely style a specific element

[self.view addStyleClassISS:@"anEvenMoreGroovyStyle"];
[self.view removeStyleClassISS:@"anEvenMoreGroovyStyle"];

Read more about how styling is applied on the Using InterfaCSS wiki page.

Stylesheets

For larger apps, it's usually a good idea to split up the styles on different stylesheet files - perhaps you want one for variables, one for common styles, and several stylesheets for different parts of the application for instance. You can also attach a scope when loading stylesheet (version 1.1), to make sure the styles it in are only processed for views under a particular view controller (for instance).

ISSStyleSheetScope* scope = [ISSStyleSheetScope scopeWithViewControllerClass:BraveNewViewController.class];
[[InterfaCSS sharedInstance] loadStyleSheetFromMainBundleFile:@"stylesForOnePartOfTheApp.css" withScope:scope];

Hot deployment of your stylesheets (for development)

To make development simpler and faster, try using an auto-refreshable stylesheet (in addition to your standard stylesheets) - load an auto-refreshable stylesheet from a (file/web) URL, launch your app on a device or in the sim, and watch how the UI updates itself before your very eyes, without having to wait for those frustrating compile/deploy/launch/returnToWhereYouWere-cycles. Note though that this feature is only intended for use during development. Checkout the snippet below for an example on how you add refreshable stylesheets (in your app delegate for instance). Also, checkout the properties stylesheetAutoRefreshInterval and processRefreshableStylesheetsLast in InterfaCSS, for more control over how refreshable stylesheets are managed.

/* For local (simulator) use, you can for instance load the actual css file used in your project as an auto-refreshable stylesheet: */
[[InterfaCSS sharedInstance] loadRefreshableStyleSheetFromLocalFile:@"/Users/username/myCoolXcodeProject/myDazzlingStyles.css"];
/* Or if you want to be able to run on a device, you can for instance simply upload the file to your cloud provider of choice: */
[[InterfaCSS sharedInstance] loadRefreshableStyleSheetFromURL:
   [NSURL URLWithString:@"http://www.mygroovycloudprovider.com/user/directory/mymyDazzlingStyles.css"]];

Getting started

Install

You can add InterfaCSS to your project in two ways:

• The simplest way is to use CocoaPods.

• Download the source and add the files in the InterfaCSS directory to your project.

Sample code

Checking out the sample code is a good way to get a feel for how InterfaCSS is used in an app. To run the sample code, do like this:

• Run pod install in the Samples/SimpleSample directory.
• Open SimpleSample.xcworkspace.
• Build and run.

Setup InterfaCSS in your app

• Load a stylesheet, like this: [[InterfaCSS sharedInstance] loadStyleSheetFromMainBundleFile:@"myDazzlingStyles.css"];. A good place to do this is in your app delegate, when your app is first launched, but if you have a lot of stylesheets it's better to defer loading of the stylesheets to when you actually need them (loadView of a particular view controller might be a better place in this case).

• Start adding styles. As with most new things, it's best to start small. For instance, don't start with adding crazily complex selectors like UIView + UITableView:nthoftype(5n+1) UITableViewCell:odd .class1 > .class2:landscape.

• Set up your view hierarchy and set some initial styles classes on your views. Check out the Using InterfaCSS page on the wiki for more details.

• Update styles as you go - use the methods provided in UIView+InterfaCSS.h and UIView+InterfaCSS.h to control the styling of your views.

• If you get stuck and starting feel the urge to break something, consider doing this first:

  • Try using -[InterfaCSS logMatchingStyleDeclarationsForUIElement:] to log the active style declarations for your view, and see if they are whay you expect them to be.

  • Enable more verbose logging by invoking [NSObject iss_setLogLevel:ISS_LOG_LEVEL_TRACE]; defined in NSObject+ISSLogSupport.h

Project status and background

Status

With the release of 1.0, InterfaCSS had finally reached the point where the most important stuff was there, and version 1.1 added a bunch of new handy features and fixes, to make InterfaCSS even more complete. But the work with refining the feature set, improving documentation and perfecting unit tests will of course continue. Also, work on a version 2.0 is currently in progress - this version will among other things focus on modularization and simplification.

And as always - all feedback is most welcome!

Background

InterfaCSS emerged out of frustration with the shortcomings of the available Interface Building tools, one of the most important being the constant need to repeat yourself when it comes to styling of user interface elements. There had to be a better way.

And out of that notion sprung the foundation of InterfaCSS, which after a spending a longish time fermenting in dark corners of various applications, finally has made a public appearance. During it's evolution into an open source project, other similar projects have popped up, although InterfaCSS still differs from most of them:

• Property names are what you expect them to be and the list of supported properties is extensive
• Powerful stylesheet syntax (selector chains, selector combinators, pseudo classes, nested declarations) that is based on the familiar CSS language used for the web
• InterfaCSS is not just for styling - it helps you with view setup and layout as well

Apps using InterfaCSS

• B. The Puffin - Prelude
• PlayMyQ - Music Player • Remote Control • Jukebox
• Zmarta

License

MIT license - see here.