A Swift extension for those who like using layout anchors && need to support pre-iOS 9
We used to do this:
self.view.addConstraint(
NSLayoutConstraint(
item: view1, attribute: .Right, relatedBy: .Equal, toItem: view2, attribute: .Left, multiplier: 1, constant: 0
)
)
Now, we can achieve the same using layout anchors:
view1.rightAnchor.constraintEqualToAnchor(view2.leftAnchor).active = true
Sadly, anchors are not supported on pre-iOS 9 devices, so I created this extension to mirror anchors. Using this extension, we write the equivalent like this:
view1.pRight.eq(view2.pLeft).active = true
As you can see, I have taken one step further to shorten the form.
.eq, .ge, and .le stands for equals, greater than or equals, and less than or equals respectively.
All available layout properties are prefixed with p. For example, pRight stands for the right layout property.
The following properties are available:
- pLeft
- pRight
- pTop
- pBottom
- pTrailing
- pLeading
- pCenterX
- pCenterY
- pWidth
- pHeight
Feel free to add your own.
Like layout anchors, layout guides are a great addition which is also available only on iOS 9 and above.
Normally, we would create a layout guide like this:
let guide = UILayoutGuide()
self.addLayoutGuide(guide)
Using this extension, we create and add the guide to view by writing the following:
let guide = view.addSupportedLayoutGuide()
addSupportedLayoutGuide() is an added method on UIView which returns an instance conforming to LayoutSupport protocol. The LayoutSupport protocol exposes the pHeight,pLeft, etc properties
For iOS 9 and above, a UILayoutGuide is returned. For pre-iOS 9, a dummy UIView is returned.
If you use addSupportedLayoutGuide to create layout guides, returned instances conform to LayoutSupport and you can only use only p properties to set up layout constraints.