xcode - 使用 NSUserDefaults 时出现未定义符号错误

Question

我在我的项目中使用了 NSUserDefaults。但是当我尝试运行我的代码时，我收到了这个错误消息。它是一个没有正确链接的框架吗？

    Undefined symbols for architecture armv7:
  "_userDefaults", referenced from:
      -[PlanItDelegate application:didFinishLaunchingWithOptions:] in PlanItDelegate.o
      -[PlanningViewController numberOfSectionsInTableView:] in PlanningViewController.o
      -[PlanningViewController tableView:cellForRowAtIndexPath:] in PlanningViewController.o
      -[PlanningViewController prepareForSegue:sender:] in PlanningViewController.o
      -[PlanningViewController tableView:titleForHeaderInSection:] in PlanningViewController.o
      -[InstellingenViewController tableView:cellForRowAtIndexPath:] in InstellingenViewController.o
      -[InstellingenViewController txtUserChanged:] in InstellingenViewController.o
      ...
ld: symbol(s) not found for architecture armv7
clang: error: linker command failed with exit code 1 (use -v to see invocation)