object - 在错误类型的对象上找不到属性？

Question

DetailViewController *dvController = [[DetailViewController alloc] initWithNibName:@"DetailView" bundle:[NSBundle mainBundle]];
dvController.selectedCollege = selectedCollege;
[self.navigationController pushViewController:dvController animated:YES];
[dvController release];
dvController = nil;

我收到错误

在第 3 行的“DetailViewController”类型的对象上找不到属性“selectedCollege”。