Flow Constraint

No more too verbose constraint! Write it like a flow!

This simple library mainly designed to tackle repetitive and too verbose code when simply setup constraint. Many 3rd party library already put syntactic sugar to build constraint but still, some will end up in repetitive and verbose enough code. Unless you make a hack of it.

Comparison

let red = UIView()
let yellow = UIView()

red.addSubview(yellow)

NSLayoutConstraint

// a must set property
yellow.translatesAutoresizingMaskIntoConstraints = false
let constraint = NSLayoutConstraint(
    item: yellow,
    attribute: .left,
    relatedBy: .equal,
    toItem: red,
    attribute: .left,
    multiplier: 1,
    constant: 20
)
constraint.isActive = true

NSLayoutAnchor

// a must set property
yellow.translatesAutoresizingMaskIntoConstraints = false
let constraint = yellow.leftAnchor.constraint(equalTo: red.leftAnchor, constant: 20)
constraint.isActive = true

If you want to set yellow edges to red edges only, you will need a lot of code, and those are repetitive task, you want to get rid of it! If you don’t, I do 😄!

Flow Constraint

yellow.flow()
    .left()
    .withSuperview()

Let’s split up the steps to build a constraint.

1. Create Flow instance to govern how do you create your constraint.

   class Flow is designed to handle all dirty interfaces to build you layout.

2. Constraint setup. There are three groups of methods available

   • Constraint

     Interfaces to govern your Constraint

     example : a. left() b. top(.bottom)

- Attribute
    > Interface to set Constraint.Attribute

    example :
        a. attribute(constant: -20)
        b. attribute(relation: .equal)

- TargetView
    > Interface to finalize Constraint setup

    example :
        a. withSuperview()
        b. withSelf()

Constraint and Attribute interfaces will need to be finalized. Every invocation will return current Flow instance which the method not marked as @discardableResult. This is correct. Since before any invocation of TargetView interface, all declared constraint not implemented using NSLayoutConstraint under the hood yet.

NOTE: Any invocation of TargetView interface will have side-effect. Invocation of TargetView is supposed to be happen after all constraint match and fixed. It will enumerate all constraint definition inside Flow instance to implement using **NSLayoutConstraint* under the hood and then remove it after*. So you can get empty and cleaned up Flow instance after any invocation of TargetView interface to define other constraint.

Example

Typically, to build edge constraint you will declare in this form in another library or using NSLayoutAnchor. This will be written in FlowConstraint equivalent.

yellow.flow().left().atrribute(constant: 20).withSuperview()
yellow.flow().top().atrribute(constant: 20).withSuperview()
yellow.flow().right().atrribute(constant: -20).withSuperview()
yellow.flow().bottom().atrribute(constant: -20).withSuperview()

You see that flow(), attribute(constant:), withSuperview() is repetitively called. It’s too verbose though it may make the code more clear 😃. I don’t like it.

Some library provide helper method with edges like SnapKit to avoid this code. But most of them will make it harder to declare constant attribute to each constraint. What if you want to make bottom to 200 instead of -20.

This if you want to make it in FlowConstraint

yellow.flow()
    .left()
    .top()
    .attribute(constant: 20)
    .withSuperview()
    // It's okay to add line spacing. Swift is powerfull!
    .right()
    .bottom()
    .attribute(constant: -20)
    .withSuperview()

Or

yellow.flow()
    .left()
    .top()
    .right()
    .bottom()
    .attribute(constant: 20, for: [.left, .top])
    .attribute(constant: -20, for: [.right, .bottom])
    .withSuperview()

Ahh, sure FlowConstraint has been provided edges for you. Just check it!

CocoaPod

Not yet ready!

Contribute

Please make your Pull Request. I’ll happy to review!

Other Libraries

• ViewDSL Combine DSL with FlowConstraint! Beautiful!
• EventClosure No more #selector on you UIControl.Event handling. Use closure!