当我的自定义 segue 动画正在执行时，目标视图显示为黑色。动画结束后，视图出现并且看起来不错。
以下是截图：
动画场景：
segue/动画完成后查看：
这是自定义 segue 类：
class SegueToPreview: UIStoryboardSegue {
override func perform() {
// Assign the source and destination views to local variables.
var firstVCView = self.sourceViewController.view as UIView!
var secondVCView = self.destinationViewController.view as UIView!
// Get the screen width and height.
let screenWidth = UIScreen.mainScreen().bounds.size.width
let screenHeight = UIScreen.mainScreen().bounds.size.height
// Specify the initial position of the destination view.
secondVCView.frame = CGRectMake(0.0, screenHeight, screenWidth, screenHeight)
// Access the app's key window and insert the destination view above the current (source) one.
let window = UIApplication.sharedApplication().keyWindow
window?.insertSubview(secondVCView, aboveSubview: firstVCView)
// Animate the transition.
UIView.animateWithDuration(0.2, animations: { () -> Void in
firstVCView.frame = CGRectOffset(firstVCView.frame, -screenWidth, 0.0)
secondVCView.frame = CGRectOffset(secondVCView.frame, -screenWidth, 0.0)
}) { (Finished) -> Void in
self.sourceViewController.presentViewController(self.destinationViewController as! UIViewController,
animated: false,
completion: nil)
}
}
虽然 unwind segue 工作得很好，但同时显示了两种视图。
我想在执行动画时没有加载视图，但不知道如何解决这个问题。