在我的视图控制器中，我有一个按钮，当按下该按钮时，输入navigationController，我的代码如下：
-(IBAction)ShangHaiButtonPressed:(id)sender{
marketviewcontroller = [[MarketViewController alloc]initWithNibName:@"MarketViewController" bundle:nil];
NSLog(@"%@",self.navigationController);
[self.navigationController pushViewController:marketviewcontroller animated:YES];
[marketviewcontroller release];
}
但是我可以看到self.navigationController为null，如何解决这个问题？谢谢。
更新：
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
_switchviewcontroller = [[SwitchViewController alloc]initWithNibName:@"SwitchViewController" bundle:nil];
[self.window addSubview:_switchviewcontroller.view];
[self.window makeKeyAndVisible];
return YES;
}
最佳答案
仅当视图控制器位于导航控制器的导航堆栈中时，视图控制器的navigationController属性才会返回有效的导航控制器对象。可以通过以下方式将视图控制器添加到导航堆栈。
通过使用initWithRootViewController：UINavigationController的方法使视图控制器成为导航控制器的rootViewController
通过使用UINavigationController的pushViewController：方法推送视图控制器。
确保以上述任何一种方式将视图控制器添加到导航堆栈中。
编辑：（在didFinishLaunchingWithOptions：代码添加到问题之后）：
将didFinishLaunchingWithOptions：方法更改为此，
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
_switchviewcontroller = [[SwitchViewController alloc]initWithNibName:@"SwitchViewController" bundle:nil];
UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:_switchviewcontroller];
[self.window addSubview:navController.view];
[navController release];
[self.window makeKeyAndVisible];
return YES;
}
Swift 4（版本）：
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey : Any]? = nil) -> Bool {
switchviewcontroller = SwitchViewController(nibName: "SwitchViewController", bundle: nil)
let navController = UINavigationController(rootViewController: switchviewcontroller)
window.addSubview(navController.view)
window.makeKeyAndVisible()
return true
}