In my case I got this error because I'd tried to save some work by creating a new project and then deleting several of the source files and copying over the source files of the same name from the working project. I also copied my MainStoryBoard file which was looking for my RootViewController. However, when I had deleted the original RootViewController and then added in the RootViewController from the previous product, evidently the Add Files operation failed to "check" the target box as suggested above. By merely visting all of the newley imported ".m" files and making sure that the target membership box was checked, all was well. I think what was happening was that the storyboard file was looking for a class that had been "excluded" from the link because the target membership was unchecked. Making sure the required files for the target are so designated in the target membership in the file inspector did the trick. Thanks Pat! (see above)

我在目标中添加了Build Phase文件，问题得到了解决。关于添加文件的步骤，请参阅我的回答:

Apple Mach-O连接器错误(APActivityIcon)

我今天在Xcode 4下将我的aaLuminate应用程序转换为Universal时出现了这个错误。 这个应用程序基于实用工具模板，最初是在Xcode 3下构建的。

为了节省时间，我将iPhone主视图和Flipside视图复制到Universal应用程序上的适当名称。我遇到了“Interface Builder file中未知类x”错误。在我的案例中，XIB文件或目标中没有任何内容。

我还复制了aaLuminate-Info。plist文件跨越其他原因-这有一个旧的关键“主nib文件基名”设置为MainWindow。

只要我删除这个关键它修复了问题!

这个问题似乎并没有过时。

我在Xcode 8中也遇到了同样的问题，并解决了类似smilebot的问题:

在Xcode中以“源代码”的形式打开故事板文件: 搜索被引用的类&删除整段

customClass = UnrecognizedClassName”

再次以“interfacebuilder - storyboard”的形式打开你的故事板文件，重新构建你的应用程序。

我在《Swift》中遇到过这种情况。

将.xib文件移动到项目的Base中。Lproj文件夹摆脱了这个错误。

在我的例子中，我使用了来自另一个项目的故事板。在看了故事板文件xml之后(例如在TextWrangler中)，我注意到一个控制器的“customModule”xml属性值是错误的(它仍然引用旧的项目)。手动更改可以解决这个问题。