1、错误：apple Mach-o Linker error
原因：compile source中有相同的.m文件
2、 self.navigationController is null
/**
*I guess your currentViewController in not in navigation controller stack hierarchy . add currentViewController to navigationcontroller should solve yr problem
*in App delegate has the window Object ,In AppDidFinishLaunching method First create object for yr firstcontroller then create NavigationControllerObject like - [[UINavigationController alloc]initWithRootViewController:yrcurrentcontroller]; [self.window addSubView:navigationController.view]
*/
3 -[NSNull countByEnumeratingWithState:objects:count:]: unrecognized selector sent to instance
如果你要是对一个数组进行forin操作
先数组里面判断有没有内容