SnapKit Constraint Sheets

Example.scs

@loginViewController {

	@formView {
		width == ^ - 32.0
		centerX == ^
		centerY == ^ + 16.0
		bottom <= ^ - 16.0

		@emailField {
			top.left.right == ^
			height == 44.0
		}

		@emailPasswordSeparator {
			top == @emailField.bottom
			left.right == ^
			height == 0.5
		}

		@passwordField {
			top == @emailPasswordSeparator.bottom
			left.right.bottom == ^
			height == 44.0
		}

	}

	@submit-button {
		width == ^ - 32.0
		top == @formView.bottom + 16.0
	}

}

Example.swift

self.formView.snp_makeConstraints { (make) -> Void in
	make.width.equalTo(self.view).offset(-32.0)
	make.centerX.equalTo(self.view)
	make.centerY.equalTo(self.view).offset(16.0)
	make.bottom.lessThanOrEqualTo(self.view).offset(-16.0)
}
self.emailField.snp_makeConstraints { (make) -> Void in
	make.top.left.right.equalTo(self.formView)
	make.height.equalTo(44.0)
}
self.emailPasswordSeparator.snp_makeConstraints { (make) -> Void in
	make.top.equalTo(self.emailField.snp_bottom)
	make.left.right.equalTo(self.formView)
	make.height.equalTo(0.5)
}
self.passwordField.snp_makeConstraints { (make) -> Void in
	make.top.equalTo(self.emailPasswordSeparator.snp_bottom)
	make.bottom.left.right.equalTo(self.formView)
	make.height.equalTo(44.0)	
}
self.submitButton.snp_makeConstraints { (make) -> Void in
	make.width.equalTo(self.formView).offset(-32.0)
	make.top.equalTo(self.formView.snp_bottom).offset(16.0)
}

This is a very early proposal for constraint style sheets for iOS Auto Layout. The main goal is to allow external files to define constraints and be reloaded whenever they are saved.

The idea is that you 'tag' each view:

self.view.snp_tag = "loginViewController"
self.formView.snp_tag = "formView"
// etc…

You would then override updateViewConstraints or updateConstraints:

override func updateViewConstraints() {
     super.updateViewConstraints()
     ConstraintStyleSheet.apply(self, ["paddingAmount": 50.0])
}