This is actually divided into two different Xcode projects called Project06a and Project06b. The first one aims to fix Project 2 to demonstrate more advanced Auto Layout techniques while also making the flags in the game stay on the screen correctly (even with landscape orientation). The second one shows Auto Layout in code.
- Inequality constraint (>=, <=, ==)
- Aspect ratio
- Equal heights
- Auto Resize
NSLayoutConstraints- Auto Layout Visual Format Language (VFL)
By default, iOS generates Auto Layout constraints for you based on a view's size and position. If we're specifying them by hand, we need to disable this feature setting the property translatesAutoresizingMaskIntoConstraints to false.
We can specify constraints using Auto Layout Visual Format Language (VFL), which is a way of "drawing" the layout you want with a series of keyboard symbols.
An example of a VFL string: "H:|[label1]|".
This string describes how we want the layout to look. The VFL string gets converted into Auto Layout constraints, then added to the view.
H:means we're defining a horizontal constraint.|means the edge of the view[label1]means putlabel1here.
In other words, this means "horizontally, I want label1 to to edge to edge in my view". What's label1? The label specified by the key "label1" in the viewsDictionary.
Other rules:
-: This symbol means space. It is 10 points by default, but it can be customized.
You can give any layout constraint a priority, and Auto Layout will do its best to make it work.
Constant priority is a value between 1 and 1000, where 1000 means this is absolutely required and anything less is optional. By default, all constraints are priority 1000.
Constraints are all evaluated from highest priority to the lowest, but ALL are taken into account.
Every UIView has a set of anchors that define its layouts rules. The most important ones are:
widthAnchorheightAnchortopAnchorbottomAnchorrightAnchorleftAnchorleadingAnchortrailingAnchorcenterXAnchorcenterYAnchor
Left and leading anchors are the same with languages that are read from left to right. However, for right-to-left languages (Hebrew and Arabic), leading and trailing flip around so that leading is equal to right and trailing is equal to left.