介绍

iOS中SpringAnimation是一种常见的动画，其效果就像弹簧一样，会在end point周围摆动几下后再回到end point，这里我们来介绍一下SpringAnimation的使用方法

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我们会用到的Method

UIView.animateWithDuration(_:, delay:, 
 usingSpringWithDamping:, 
 initialSpringVelocity:, options:, 
 animations:, completion:)

这次的函数相比上次增加了两个参数:

• usingSpringWithDamping: 参数的范围为0.0f到1.0f，数值越小「弹簧」的振动效果越明显。可以视为弹簧的劲度系数
• initialSpringVelocity: 表示动画的初始速度，数值越大一开始移动越快。

Demo

继续上次的Demo，我们在viewWillAppear中先修改控件位置

  override func viewWillAppear(animated: Bool) {
    super.viewWillAppear(animated)
    heading.center.x -= view.bounds.width
    username.center.x -= view.bounds.width
    password.center.x -= view.bounds.width
    loginButton.center.y += 30.0
    loginButton.alpha = 0
    }
    ```
##加特技!
隐藏登录按钮

UIView.animateWithDuration(1.0, delay: 0.8, usingSpringWithDamping: 0.5, initialSpringVelocity: 0, options: UIViewAnimationOptions.CurveEaseOut, animations: { () -> Void in
//先隐藏登录按钮
self.loginButton.center.y -= 30.0
self.loginButton.alpha = 1.0
}, completion: nil)
```

在viewDidAppear方法中，使用Spring动画使按钮弹出，同时透明度变成1
UIView.animateWithDuration(1.0, delay: 0.8, usingSpringWithDamping: 0.5, initialSpringVelocity: 0, options: UIViewAnimationOptions.CurveEaseOut, animations: { () -> Void in self.loginButton.center.y -= 30.0 self.loginButton.alpha = 1.0 }, completion: nil)

点击按钮时按钮的动画效果

@IBAction func login() {
view.endEditing(true)
    
let bounds = self.loginButton.bounds
//使按钮的位置向下移动20，宽度增加80
UIView.animateWithDuration(1.5, delay: 0.0, usingSpringWithDamping: 0.2, initialSpringVelocity: 20, options: UIViewAnimationOptions.CurveEaseInOut, animations: { () -> Void in
        self.loginButton.bounds = CGRect(x: bounds.origin.x-20, y: bounds.origin.y, width: bounds.size.width+80, height: bounds.size.height)
        }) { _ in
            //完成的动作
}
    //spinner出现，调整位置，调整Button颜色
    UIView.animateWithDuration(0.33, delay: 0, options: UIViewAnimationOptions.CurveEaseInOut, animations: { () -> Void in
        self.loginButton.center.y += 60
        self.spinner.alpha = 1.0
        self.spinner.center = CGPoint(x: 40, y: self.loginButton.frame.size.height/2)
        self.loginButton.backgroundColor = UIColor(red: 0.85, green: 0.83, blue: 0.45, alpha: 1.0)
        
        }, completion: nil)
    
  }