ios - 过渡时的 fatal error

Question

Error : "fatal error: unexpectedly found nil while unwrapping an Optional value" during transition between two view on same view controller

当我调用 Flip1 函数时，出现上述错误。

代码如下:

@IBAction func Flip(_ sender: AnyObject){
    UIView.transition(from: Back, to: Front, duration: 0.5, options: UIViewAnimationOptions.transitionFlipFromLeft, completion: nil)
}

@IBAction func Flip1(_ sender: AnyObject){
    UIView.transition(from: Front, to: Back, duration: 1, options: UIViewAnimationOptions.transitionFlipFromRight, completion: nil)
}

Answer 1

是的，我终于发现了错误。

只需将 outlet 设为强引用或弱引用即可:

@IBOutlet var Front: UIView!
@IBOutlet var Back: UIView!

完成了!