为什么self.navigationController变成了nil？

Question

我有这段代码：

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

我是第一行，self.navigationController有一个值。

在第二行，它的值变为0.为什么？

Answer 1

除非你已经覆盖了initWithNibName：bundle：在ViewController2中做一些真正不幸的事情，你所说的话几乎没有机会成真。

如果使用以下断言更改代码，断言是否真的会触发？

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];