我用.Old|创建了一个观察者.新的选项。在处理程序方法中,我尝试获取前后值,但编译器提示:'NSString'isnotconvertibleto'NSDictionaryIndex:NSObject,AnyObjectoverridefuncobserveValueForKeyPath(keyPath:String!,ofObjectobject:AnyObject!,change:[NSObject:AnyObject]!,context:UnsafeMutablePointer){letapprovedOld=change[NSKeyValueChangeOldKey]asBo