在几个用户的帮助和一些额外搜索的帮助下，我能够找出问题的原因。

With the help of a couple of users and some added searching, I was able to figure out the cause of my problem.

根据前面提到的用户的建议，我将 NSCoding 协议添加到我的 CalendarEvent 类。

Per the suggestion of the previously mentioned users, I added the NSCoding protocol to my CalendarEvent class.

class CalendarEvent : NSObject, NSCoding {
    ....
}

不幸的是，这并没有完全解决问题，但这是一个开始。一些错误和快速搜索显示我必须更改此内容：

Unfortunately, that didn't completely fix the issue, but it was a start. A few errors and a quick search showed me that I had to change this:

init(withCoder coder : NSCoder){
    ....
}
func encodeWithCoder(coder : NSCoder){
    ....
}

到此：

required init(coder : NSCoder) {
    ....
}
func encode(with aCoder : NSCoder) {
    ....
}

进行这些更改后，我的代码运行得非常好。

After making those changes, my code ran perfectly fine.