IOS开发笔记：编译时出现的错误

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

IOS开发笔记：编译时出现的错误

原文：http://www.cnblogs.com/hl-iOS/p/4843700.html