Stevia 🍃 - Human readable Auto Layout

Reason - Example - Live Reload - Installation - Documentation

layout(
    100,
    |-email-| ~ 80,
    8,
    |-password-| ~ 80,
    "",
    |login| ~ 80,
    0
)

Reason

Why

Because nothing holds more truth than pure code 🤓
Xibs and storyboards are heavy, hard to maintain, hard to merge.
They split the view concept into 2 separate files making debugging a nightmare
There must be a better way

How

By creating a tool that makes Auto layout code finally readable by a human being.
By coupling it with live code injection such as injectionForXcode we can design views in real time
View layout becomes fun, concise, maintainable and dare I say, beautiful ❤️

What

• Auto Layout DSL
• Pure Swift
• Simple, this is just NSLayoutConstraint shortcuts, pure UIKit code, no voodoo magic
• Chainable api

Advantages of Stevia

• No more constraints hell in Interface builder.
• No more debugging in Interface builder toggling checkboxes.
• The view code is not split between 2 files anymore
• What you see is what you get, your view code is in one place, there is no hidden logic elsewere (in the xib)
• No more referencing Storyboards or Xibs by their names "ProfileStoryboard". We all know strings are bad identifiers.
• Clear view Hierarchy
• Live reload, WHAT YOU SEE IS WHAT YOU GET
• Events are a breeze
• Code views Faster
• No more XML (Thank God!)
• Better readability 1000lines XML file vs. 30lines code
• Readable constraints (they actually look like the layout itself \o/)
• Horizontal & vertical layout can be described at the same time
• Styles are well separated, concise, reusable and can be composed
• Content like text, placeholders are easier to visualize

Login View Example

Before (Native Autolayout)

class LoginViewNative:UIView {

    let email = UITextField()
    let password = UITextField()
    let login = UIButton()

    convenience init() {
        self.init(frame:CGRectZero)
        backgroundColor = .whiteColor()

        addSubview(email)
        addSubview(password)
        addSubview(login)

        email.translatesAutoresizingMaskIntoConstraints = false
        password.translatesAutoresizingMaskIntoConstraints = false
        login.translatesAutoresizingMaskIntoConstraints = false

        addConstraint(NSLayoutConstraint(
                item: email,
                attribute: .Left,
                relatedBy: .Equal,
                toItem: self,
                attribute: .Left,
                multiplier: 1,
                constant: 8)
        )
        addConstraint(NSLayoutConstraint(
                item: email,
                attribute: .Right,
                relatedBy: .Equal,
                toItem: self,
                attribute: .Right,
                multiplier: 1,
                constant: -8)
        )
        addConstraint(NSLayoutConstraint(
            item: password,
            attribute: .Left,
                relatedBy: .Equal,
                toItem: self,
                attribute: .Left,
                multiplier: 1,
                constant: 8)
        )
        addConstraint(NSLayoutConstraint(
            item: password,
            attribute: .Right,
            relatedBy: .Equal,
            toItem: self,
            attribute: .Right,
            multiplier: 1,
            constant: -8)
        )
        addConstraint(NSLayoutConstraint(
            item: login,
            attribute: .Left,
            relatedBy: .Equal,
            toItem: self,
            attribute: .Left,
            multiplier: 1,
            constant: 0)
        )
        addConstraint(NSLayoutConstraint(
            item: login,
            attribute: .Right,
            relatedBy: .Equal,
            toItem: self,
            attribute: .Right,
            multiplier: 1,
            constant: 0)
        )
        for b in [email, password, login] {
            addConstraint(NSLayoutConstraint(
                item: b,
                attribute: .Height,
                relatedBy: .Equal,
                toItem: nil,
                attribute: .NotAnAttribute,
                multiplier: 1,
                constant: 80)
            )
        }
        addConstraint(NSLayoutConstraint(
            item: email,
            attribute: .Top,
            relatedBy: .Equal,
            toItem: self,
            attribute: .Top,
            multiplier: 1,
            constant: 100)
        )
        addConstraint(NSLayoutConstraint(
            item:email,
            attribute: .Bottom,
            relatedBy: .Equal,
            toItem: password,
            attribute: .Top,
            multiplier: 1,
            constant: -8)
        )
        addConstraint(NSLayoutConstraint(
            item: login,
            attribute: .Bottom,
            relatedBy: .Equal,
            toItem: self,
            attribute: .Bottom,
            multiplier: 1,
            constant: 0)
        )

        email.placeholder = "Email"
        email.borderStyle = .RoundedRect
        email.autocorrectionType = .No
        email.keyboardType = .EmailAddress
        email.font = UIFont(name: "HelveticaNeue-Light", size: 26)
        email.returnKeyType = .Next

        password.placeholder = "Password"
        password.borderStyle = .RoundedRect
        password.font = UIFont(name: "HelveticaNeue-Light", size: 26)
        password.secureTextEntry = true
        password.returnKeyType = .Done

        login.setTitle("Login", forState: .Normal)
        login.backgroundColor = .lightGrayColor()
        login.addTarget(self, action: "loginTapped", forControlEvents: .TouchUpInside)
        login.setTitle(NSLocalizedString("Login", comment: ""), forState: .Normal)
    }

    func loginTapped() {
        //Do something
    }
}

With Stevia 🍃

class LoginViewStevia:UIView {

    let email = UITextField()
    let password = UITextField()
    let login = UIButton()

    convenience init() {
        self.init(frame:CGRectZero)
        backgroundColor = .whiteColor()

        sv(
            email.placeholder("Email").style(fieldStyle), //.style(emailFieldStyle),
            password.placeholder("Password").style(fieldStyle).style(passwordFieldStyle),
            login.text("Login").style(buttonStyle).tap(loginTapped)
        )

        layout(
            100,
            |-email-| ~ 80,
            8,
            |-password-| ~ 80,
            "",
            |login| ~ 80,
            0
        )
    }

    func fieldStyle(f:UITextField) {
        f.borderStyle = .RoundedRect
        f.font = UIFont(name: "HelveticaNeue-Light", size: 26)
        f.returnKeyType = .Next
    }

    func passwordFieldStyle(f:UITextField) {
        f.secureTextEntry = true
        f.returnKeyType = .Done
    }

    func buttonStyle(b:UIButton) {
        b.backgroundColor = .lightGrayColor()
    }

    func loginTapped() {
        //Do something
    }
}

Number of lines From 144 -> 57 ( ~ divided by 2.5)
Number of characters From 4231 -> 1338 ( ~ divided by 3)

Write 3 times less code that is actually 10X more expressive and maintainable <3

Live Reload

You can even enable LiveReload during your development phase! 🎉🎉🎉

Stevia + InjectionForXcode = <3 (WhoNeedsReactNative??) 🚀

• Download InjectionForXcode

• Install it, Launch it and Go to File>Install Plugins (cmd+i)

• Restart Xcode and make sure to click Load bundles on the popup

In order to support live reload with InjectionForXcode, we simply need to tell our ViewController to rebuild a view after an injection occured.

in viewDidLoad() add :

on("INJECTION_BUNDLE_NOTIFICATION") {
    self.view = MyView()
}

Currently InjectionForXcode doesn't seem to swizzle init methods for some reason. So we have to move our view code in another methods

convenience init() {
    self.init(frame:CGRectZero)
    //View code
}

Becomes

convenience init() {
    self.init(frame:CGRectZero)
    render()
}

func render() {
  //View code
}

And Voila :)

Now you can launch the app and modify whatever you want in the render() method. simply hit ^= or Product>Inject source and you'll see your changes Live ! 🎉🎉🎉

Installation

CocoaPods

pod 'SteviaLayout'
use_frameworks!

Carthage

github "s4cha/Stevia"

• Create a Cartfile file at the root of your project folder

• Add github "s4cha/Stevia" to your Cartfile

• Run carthage update

• Drag and drop Stevia.framework from /Carthage/Build/iOS/ to Linked frameworks and libraries in Xcode (Project>Target>General>Linked frameworks and libraries)

• Add new run script (Project>Target>Build Phases>+> New run script phase) /usr/local/bin/carthage copy-frameworks

• Add Input files $(SRCROOT)/Carthage/Build/iOS/Stevia.framework

There you go!

Manual

Copy Stevia source files to your Xcode project

Documentation

View Hierarchy

sv(
    subview1,
    subview2,
    subview3
)

sv([]) and sv() are essentially shortcuts that call addSubview() and
view.translatesAutoresizingMaskIntoConstraints = false

It also has the benefit of being very visual so that your can actually see what the view hierarchy is. This is especially true for nested hierarchies :

sv(
    subview1,
    subview2.sv(
        nestedView1,
        nestedView2̨
    ),
    subview3
)

Horizontal layout

This is intended to look like Apple's visual format, so you should be very familiar with the syntax.
Stevia only removes the [] and the String.

Stick a label to the left of the screen

|label

With the default margin (8)

|-label

With a custom margin

|-42-label

Just to be very clear we want to emphasize that this is pure syntactic sugar.
This equivalent of the following using the chainable api :

label.left(42)

Which in turn will create Native Autolayout constraints :

label.superview?.addConstraint(
  NSLayoutConstraint(
    item: label,
    attribute:.Left,
    relatedBy: .Equal,
    toItem: label.superview!,
    attribute:.Left,
    multiplier: 1,
    constant: 42
  )
)

Combine all at once.

|-avatar-15-name-20-followButton-|

Vertical layout

avatar.top(50)

==

layout(
    50,
    avatar
  )

While using layout for a single element might seem a bit overkill, it really shines when combined with horizontal layout.
Then we have the full layout in one place (hence the name).

layout(
    50,
    |-15-avatar.size(60)
  )

The avatar is 50px from the top with a left margin of 15px and a size of 60px

Another great example is the login view, representable in one single statement !

layout(
    100,
    |-email-| ~ 80,
    8,
    |-password-| ~ 80,
    "",
    |login| ~ 80,
    0
)

In case you wonder ~ operator == .height(x), it's just more readable in a layout statement that way.

Chainable Api

The avatar example above could've been written that way using the chainable api :

avatar.top(50).left(15).size(50)

Using layout is just clearer in most of the cases but it's yours to choose which way you prefer :)

Centering

Horizontally

imageView.centerHorizontally()

Vertically

imageView.centerVertically()

On both axis

imageView.centerInContainer()

Alignment

Horizontally

alignHorizontally(avatar,name,followButton)

Vertically

alignVertically(title,subtitle,text)

Align the center of one view with another one :

alignCenter(view1, with: view2)

In the example above of a follow Cell, here is how the layout code would look like :

|-avatar-15-name-20-followButton-|
alignHorizontally(avatar,name,followButton)

But |-avatar-15-name-20-followButton-| actually returns the array of views!!! so we can write it in one single statement :

alignHorizontally(|-avatar-15-name-20-followButton-|)

🎉🎉🎉

Button taps

button.addTarget(self, action: "follow", forControlEvents: .TouchUpInside)

Becomes:

button.tap(follow)

This is shorter and less error-prone since follow is is not referenced by a string value anymore \o/

Styles

Well, just call style on a UIView subclass :

In-line for small or unique styles

detail.style { l in
  l.numberOfLines = 0
  l.textAlignment = .Center
  l.textColor = .blueColor()
  l.text = NSLocalizedString("NeedPetMessage", comment: "")
}

Or in a separate to make them reusable

// My style method, kinda like CSS
func detailStyle(l:UILabel) {
  l.numberOfLines = 0
  l.textAlignment = .Center
  l.textColor = .blueColor()
  l.text = NSLocalizedString("NeedPetMessage", comment: "")
}

// Later
{
  // Set my style
  detail.style(detailStyle)
}

This is the preferred way because the styles become reusable and composable: you can chain them! You can even create a Style File grouping high level functions for common styles. Usage then becomes very similar to CSS!

Content

button.setTitle("Hello", forState: .Normal)

Becomes :

button.text("Hello")

button.setImage(UIImage(named:"CommentIcon"), forState: .Normal)

Becomes :

button.image("CommentIcon")

Rationale behind the project

On the Yummypets app, we needed to deal with looooooots of views.
After trying different methods for building views (Xibs, Storyboards, Splitting Storyboards, React Native even(!).
We found that coding views programmatically was the best solution for us. But coding views programmatically had its issues too: UIKit exposes an imperative, verbose API, and it's really easy to create a mess with it. That's why we created Stevia.

Contributors

YannickDot, S4cha, Damien, Snowcraft, Mathieu-o

Other repos ❤️

Stevia 🍃 is part of a series of lightweight libraries aiming to make developing iOS Apps a breeze :

• Async code : then
• JSON WebServices : ws
• JSON Parsing : Arrow