一共有三个viewController
,MainViewController
ViewControllerB
和ViewControllerC
。
MainViewController
将在应用启动时加载。
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
// Override point for customization after application launch.
self.window = [[UIWindow alloc]initWithFrame:[[UIScreen mainScreen] bounds]];
MainViewController * main = [[MainViewController alloc]init];
UINavigationController * navigationController = [[UINavigationController alloc]initWithRootViewController:main];
self.window.rootViewController = navigationController;
self.window.backgroundColor = [UIColor whiteColor];
[self.window makeKeyAndVisible];
[[UIApplication sharedApplication] setStatusBarStyle:UIStatusBarStyleLightContent];
return YES;
}
在MainViewController
上有一个button
, present ViewControllerB
,
UIViewController *rootViewController = [[UIApplication sharedApplication].keyWindow rootViewController];
ViewControllerB * vcb=[[ViewControllerB alloc] init];
[rootViewController presentViewController:vcb animated:YES completion:nil];
ViewControllerB
出现后,点击按钮push ViewController
C。
但是 navigationController
是 nil
。它无法推送 ViewControllerC
[self.navigationController pushViewController:vcC animated:YES];
最佳答案
您有 MainViewController (mvc),它嵌入在 NavigationController 中;
然后,在 mvc 上,您有以下代码:
[rootViewController presentViewController:vcb animated:YES completion:nil];
您正在当前 ViewController 上调用
presentViewController
,它将模态呈现下一个 ViewController,在本例中为 ViewControllerB (vcb);最后,您尝试访问 ViewControllerB (vcb) 中的 NavigationController 以推送 ViewControllerC (vcc),使用以下代码:
[self.navigationController pushViewController:vcC animated:YES];
问题是 vcb 不知道 NavigationController,因为 presentViewController
在现有导航堆栈之外以模态方式呈现 View Controller 。因此,在 vcb 中产生一个 nil NavigationController。
可以引用https://stackoverflow.com/a/14233252/9323816获取更多信息。
关于ios - navigationController 为 nil,当推送 viewcontroller 时,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/50001505/