autolayout之VFL 语法回顾

 public class NSLayoutConstraint : NSObject {
    
    /* Create an array of constraints using an ASCII art-like visual format string.
     */
    public class func constraintsWithVisualFormat(format: String, options opts: NSLayoutFormatOptions, metrics: [String : AnyObject]?, views: [String : AnyObject]) -> [NSLayoutConstraint]
    
    /* This macro is a helper for making view dictionaries for +constraintsWithVisualFormat:options:metrics:views:.  
     NSDictionaryOfVariableBindings(v1, v2, v3) is equivalent to [NSDictionary dictionaryWithObjectsAndKeys:v1, @"v1", v2, @"v2", v3, @"v3", nil];
     */
    
    // not for direct use
    
    /* Create constraints explicitly.  Constraints are of the form "view1.attr1 = view2.attr2 * multiplier + constant" 
     If your equation does not have a second view and attribute, use nil and NSLayoutAttributeNotAnAttribute.
     */
    public convenience init(item view1: AnyObject, attribute attr1: NSLayoutAttribute, relatedBy relation: NSLayoutRelation, toItem view2: AnyObject?, attribute attr2: NSLayoutAttribute, multiplier: CGFloat, constant c: CGFloat)
    
    /* If a constraint's priority level is less than UILayoutPriorityRequired, then it is optional.  Higher priority constraints are met before lower priority constraints.
     Constraint satisfaction is not all or nothing.  If a constraint 'a == b' is optional, that means we will attempt to minimize 'abs(a-b)'.
     This property may only be modified as part of initial set up.  An exception will be thrown if it is set after a constraint has been added to a view.
     */
    public var priority: UILayoutPriority
    
    /* When a view is archived, it archives some but not all constraints in its -constraints array.  The value of shouldBeArchived informs UIView if a particular constraint should be archived by UIView.
     If a constraint is created at runtime in response to the state of the object, it isn't appropriate to archive the constraint - rather you archive the state that gives rise to the constraint.  Since the majority of constraints that should be archived are created in Interface Builder (which is smart enough to set this prop to YES), the default value for this property is NO.
     */
    public var shouldBeArchived: Bool
    
    /* accessors
     firstItem.firstAttribute {==,<=,>=} secondItem.secondAttribute * multiplier + constant
     */
    unowned(unsafe) public var firstItem: AnyObject { get }
    public var firstAttribute: NSLayoutAttribute { get }
    public var relation: NSLayoutRelation { get }
    unowned(unsafe) public var secondItem: AnyObject? { get }
    public var secondAttribute: NSLayoutAttribute { get }
    public var multiplier: CGFloat { get }
    
    /* Unlike the other properties, the constant may be modified after constraint creation.  Setting the constant on an existing constraint performs much better than removing the constraint and adding a new one that's just like the old but for having a new constant.
     */
    public var constant: CGFloat
    
    /* The receiver may be activated or deactivated by manipulating this property.  Only active constraints affect the calculated layout.  Attempting to activate a constraint whose items have no common ancestor will cause an exception to be thrown.  Defaults to NO for newly created constraints. */
    @available(iOS 8.0, *)
    public var active: Bool
    
    /* Convenience method that activates each constraint in the contained array, in the same manner as setting active=YES. This is often more efficient than activating each constraint individually. */
    @available(iOS 8.0, *)
    public class func activateConstraints(constraints: [NSLayoutConstraint])
    
    /* Convenience method that deactivates each constraint in the contained array, in the same manner as setting active=NO. This is often more efficient than deactivating each constraint individually. */
    @available(iOS 8.0, *)
    public class func deactivateConstraints(constraints: [NSLayoutConstraint])
  }

self.view.addSubview(button1)
self.view.addSubview(button2)
button1.translatesAutoresizingMaskIntoConstraints = false
button2.translatesAutoresizingMaskIntoConstraints = false
let views = ["button1":button1,"button2":button2]
self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("H:|-10-[button1(30)]->=30-[button2(30)]", options: NSLayoutFormatOptions(rawValue:0), metrics: nil, views: views))

self.view.addConstraints(NSLayoutConstraint.constraintsWithVisualFormat("V:|-value-[button1(30)]", options: NSLayoutFormatOptions(rawValue:0), metrics: ["value":20], views: views))
self.view.addConstraint(NSLayoutConstraint(item: button2, attribute: .CenterY, relatedBy: .Equal, toItem: button1, attribute: .CenterY, multiplier: 1, constant: 0))
self.view.addConstraint(NSLayoutConstraint(item: button2, attribute: .Height, relatedBy: .Equal, toItem: button1, attribute: .Height, multiplier: 1, constant: 0))

 /* By default, the autoresizing mask on a view gives rise to constraints that fully determine 
     the view's position. This allows the auto layout system to track the frames of views whose 
     layout is controlled manually (through -setFrame:, for example).
     When you elect to position the view using auto layout by adding your own constraints, 
     you must set this property to NO. IB will do this for you.
     */
    @available(iOS 6.0, *)
    public var translatesAutoresizingMaskIntoConstraints: Bool // Default YES

self.view.removeConstraints(self.view.constraints)