在最新的Xcode版本中，我已经两次遇到过这种情况。
在这两种情况下我都需要对UIViewController的XIB文件进行更改（在这种情况下，它将是MapViewController.xib：

This happened to me already twice in the newest Xcode release. In both cases I needed to make changes to the UIViewController's XIB file (In you case it would be MapViewController.xib:

BEFORE：

1. 将主视图移出查看控制器的子项：


2. 从XIB中移除查看控制器（由于文件的所有者已经是其类，因此没有必要）：

1. Move main View out of View Controller's children:
2. Remove View Controller from the XIB (it is not necessary since File's Owner should be of its Class already):

之后：