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Stevia

Stevia is an iOS Auto Layout DSL written in swift.

It is not a heavy layout engine, it is just a lightweight shortcut api for creating Auto Layout constraints and defining view only using code ! 😍

N

  • Layout
  • Component styling
  • Event handling

Advantages of Stevia over the classic way

  • The view hierachy is clearer
  • Constraints are (WAY) more readable, 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
  • Events are a breeze

Less code + More readable ==> easier to maintain

Teaser ... ❤️

Layout

layout([
    100,
    |-emailField-|      ~ 80,
    8,
    |-passwordField-|   ~ 80,
    "",
    |button|            ~ 80,
    0
])

Taps handling

button.tap(loginTapped)

Localized text

button.textKey("Login")

Notifications

on(UIApplicationDidBecomeActiveNotification, refresh)

Show me the code!

Turn this legacy code ...

addConstraint(NSLayoutConstraint(
        item: emailField,
        attribute: .Left,
        relatedBy: .Equal,
        toItem: self,
        attribute: .Left,
        multiplier: 1,
        constant: 8)
)
addConstraint(NSLayoutConstraint(
        item: emailField,
        attribute: .Right,
        relatedBy: .Equal,
        toItem: self,
        attribute: .Right,
        multiplier: 1,
        constant: 8)
)
addConstraint(NSLayoutConstraint(
    item: passwordField,
    attribute: .Left,
        relatedBy: .Equal

    // [...] (80+ more lines ...)
    //
    // CENSORED.
    // We decided to strip that part because it was WAAYY TO LONG ... 🙉🙈🙊

... into this !

layout([
    100,
    |-emailField-|      ~ 80,
    8,
    |-passwordField-|   ~ 80,
    "",
    |button|            ~ 80,
    0
])

Maybe you prefer Visual Format ?

let views = ["emailField":emailField, "passwordField":passwordField]
addConstraints(NSLayoutConstraint.constraintsWithVisualFormat(
  "V:|-[emailField]-|",
  options: NSLayoutFormatOptions(rawValue: 0),
  metrics: nil,
  views: views)
)

we got your back 😘

views = ["emailField":emailField, "passwordField":passwordField]
v("|-[emailField]-|")

But what about using this instead !? Much better ❤️

|-emailField-|

We personally try to avoid visual format because it's more error prone. Plus the compiler has got you covered with this one :)

Components hierarchy

This ...

addSubview(emailField)
addSubview(passwordField)
addSubview(button)

into this !

sv([
    emailField,
    passwordField,
    button
])

Styling elements

This ...

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

into this !

emailField.style { f in
    f.borderStyle = .RoundedRect
    f.autocorrectionType = .No
    f.keyboardType = .EmailAddress
    f.font = UIFont(name: "HelveticaNeue-Light", size: 26)
    f.returnKeyType = .Next
}

Events handling

This

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

Into this !

 button.tap(loginTapped)

Real life example : a classic Login View

alt text

Before Stevia

class LoginView:UIView {

    let emailField = UITextField()
    let passwordField = UITextField()
    let button = UIButton()

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

        addSubview(emailField)
        addSubview(passwordField)
        addSubview(button)

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

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

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

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

    func loginTapped() {
    //Do something
    }
}

Stevia: On

class LoginView:UIView {

    let emailField = UITextField()
    let passwordField = UITextField()
    let name = UITextField()
    let button = UIButton()

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

        sv([
            emailField.placeholder("Email").style(fieldStyle).style(emailFieldStyle),
            passwordField.placeholder("Password").style(fieldStyle).style(passwordFieldStyle),
            button.text("Login").tap(loginTapped).style(buttonSytle)
        ])

        layout([
            100,
            |-emailField-|      ~ 80,
            8,
            |-passwordField-|   ~ 80,
            "",
            |button|            ~ 80,
            0
        ])
    }

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

    func emailFieldStyle(f:UITextField) {
        f.autocorrectionType = .No
        f.keyboardType = .EmailAddress
    }

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

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

    func loginTapped() {
    //Do something
    }
}

Rationale behind the project

Easy or simple ?

We know some things can look "easy" but be very complex under the hood. We tried to keep both. We wanted Stevia to be easy to use while remaining very simple. Most of Stevia's code is just simple shortcuts to UIKit Api. Nothing prevents you from mixing Stevia with pure UIKit code. Because Stevia IS pur UIKit code.

Why Stevia?

At Yummypets we have loooots of views.

After trying diferent methods for building views (Xibs, Storyboard, Splitting Storyboards) React Native even! We found that coding views programatically was the best solution.

Why ? Because CODE DON'T LIE

But coding views programatically had its issues too.

That's why we created Stevia.

Advantages of UIView swift class over Xibs or storyboards

  • Better readability consise ex: 1000lines XMl file vs. 30lines code
  • No more XML (Thank God!)
  • 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 refrencing Storyboards or Xibs by their names "ProfileStoryboard". We all know strings are bad identifiers.

Next

  • Live reload
  • Documenting Stevia shortcuts

Contributors

YannickDot, S4cha, Damien