为什么self.navigationController成为零？

Question

我有这样的代码：

ViewController2 *childView = [[ViewController2 alloc] initWithNibName:@"ViewController2" bundle:nil]; 
[self.navigationController pushViewController:childView animated:YES]; 

我的第一行，self.navigationController具有值。

在第二行，它的值变为0.为什么？

Answer 1

除非你重写了initWithNibName：bundle：在ViewController2中做了一件真正不幸的事情，那么你所说的可能是真的很少。

如果你用这个下面的断言改变你的代码，断言是否真的触发？

UINavigationController* navigationController = self.navigationController; 
ViewController2 *childView = [[ViewController2 alloc] initWithNibName:@"ViewController2" bundle:nil]; 
NSAssert(navigationController == self.navigationController, @"I was removed from the navigation controller!"); 
[self.navigationController pushViewController:childView animated:YES];