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Applications are expected to have a root view controller at the end of application launch
问题：Applications are expected to have a root view controller at the end of application launch环境：XCode4.2
场景：这种问题多发生在XCode4.2 移植低版本项目时出现。
原因：在iOS5下，应用加载时，需要一个root view controller，在iOS5以下的版本会有MainWindow作为启动文件，iOS5以上没有了。
解决方案：手动创建一个root view controller，在application:didFinishLaunchingWithOptions中添加如下方法，同时为了避免新增加的view对已有的程序产生影响，把ViewController.xib文件的Alpha值设置为0，即完全透明。
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
// ===========add code===========
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
self.viewController = [[ViewController alloc] initWithNibName:@"ViewController" bundle:nil];
//self.viewController = [[ViewController alloc] init];
self.window.rootViewController = self.viewController;
// ===========add code============
[self showTabBarController:1];
[self.window makeKeyAndVisible];
return YES;
}
最后更新：2017-04-02 22:16:01