如何将视图控制器和.xib文件链接到xcode 4中的标签栏项目

I have a tab bar with 4 items and i want to link the .xib files to each item. The problem is that the NIB File Name shows no items, and if i write the .xib for example, StartView without the .xib i get an error. I get the same error when i link the tab item to the view controller class in the Identity Inspector. This is the error: I have a tab bar with 4 items and i want to lin