iOS Core Animation详解（四）AutoLayout中的动画_html/css_WEB-ITnose

前言：AutoLayout定义了View的位置，也就是说，在Auto Layout的工程里，如果不修改约束本身，在视图重新绘制的时候，还会回到最开始的位置。AutoLayout中的动画与视图的位置和大小有关。

先看看效果

实现过程

在Storyboard上拖拽一个UIImageview。设置约束为：水平垂直正中心，大小很定100＊100

拖拽Imageview以及Constraint为Outlet

注意拖拽Y相关的约束，也就是这个

对应代码

@IBOutlet weak var imageview: UIImageView! @IBOutlet weak var yConstraints: NSLayoutConstraint!

在viewDidload中设置imageview的初始状态

yConstraints.constant = yConstraints.constant - CGRectGetHeight(UIScreen.mainScreen().bounds)/2 self.imageview.alpha = 0.0; self.imageview.transform = CGAffineTransformMakeScale(0.1, 0.1) self.view.layoutIfNeeded();

ViewWillAppear中创建动画

yConstraints.constant = yConstraints.constant + CGRectGetHeight(UIScreen.mainScreen().bounds)/2 UIView.animateWithDuration(1.0, animations: { () -> Void in        self.imageview.alpha = 1.0        self.imageview.transform = CGAffineTransformIdentity        self.view.layoutIfNeeded() })

原理

原理比较简单，就是利用修改约束NSLayoutConstraint中的属性constant，然后调用layoutIfNeeded来实现动画。注意，属性multiplier目前（iOS 8.4）还是只读的,不能修改。但是可以通过关系view1.property = view2.property * multiplier + constant进行转换。

纯代码的AutoLayout动画

上述动画用纯代码实现

class ViewController: UIViewController {    var imageview:UIImageView?    weak var yConstraint:NSLayoutConstraint?    override func viewDidLoad() {        super.viewDidLoad()        //添加Imageview        let image = UIImage(named: "1_hello_hwc.jpg")        imageview = UIImageView(image: image)        self.imageview?.setTranslatesAutoresizingMaskIntoConstraints(false)        self.view.addSubview(self.imageview!)        //创建约束，定义最开始的位置        let hC = NSLayoutConstraint(item:self.view, attribute:NSLayoutAttribute.CenterX, relatedBy: NSLayoutRelation.Equal, toItem: self.imageview, attribute: NSLayoutAttribute.CenterX, multiplier: 1.0, constant: 0.0)        let vC = NSLayoutConstraint(item:self.view, attribute:NSLayoutAttribute.CenterY, relatedBy: NSLayoutRelation.Equal, toItem: self.imageview, attribute: NSLayoutAttribute.CenterY, multiplier: 1.0, constant: 0.0)        yConstraint = vC;        yConstraint!.constant = yConstraint!.constant - CGRectGetHeight(UIScreen.mainScreen().bounds)/2        let widthC = NSLayoutConstraint(item:self.imageview!, attribute: NSLayoutAttribute.Width, relatedBy: NSLayoutRelation.Equal, toItem:nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1.0, constant: 100)        let widthH = NSLayoutConstraint(item:self.imageview!, attribute: NSLayoutAttribute.Height, relatedBy: NSLayoutRelation.Equal, toItem:nil, attribute: NSLayoutAttribute.NotAnAttribute, multiplier: 1.0, constant: 100)        self.view.addConstraints([hC,vC,widthC,widthH])        //定义最开始的状态        self.imageview?.alpha = 0.0;        self.imageview?.transform = CGAffineTransformMakeScale(0.1, 0.1);        self.view.layoutIfNeeded()    }    override func viewWillAppear(animated: Bool) {        yConstraint!.constant = yConstraint!.constant + CGRectGetHeight(UIScreen.mainScreen().bounds)/2        UIView.animateWithDuration(1.0, animations: { () -> Void in            self.imageview!.alpha = 1.0            self.imageview!.transform = CGAffineTransformIdentity            self.view.layoutIfNeeded()        })    }}

定位Constraints

设置属性identifier

yConstraint.identifier ＝ "identifier"

然后在过滤，定义到这个Constraints,

let constraint =  filter(self.view.constraints() as! [NSLayoutConstraint], { (constraint:NSLayoutConstraint) -> Bool in return constraint.identifier == "identifier" }).first