1.首先，让Controller遵守NavigationController代理。
self.navigationController.delegate=self;
写完这句话之后发现要遵守协议
2.然后点进去协议，实现方法
- (nullableid)navigationController:(UINavigationController*)navigationController
animationControllerForOperation:(UINavigationControllerOperation)operation
fromViewController:(UIViewController*)fromVC
toViewController:(UIViewController*)toVC {
returnself;
}
注意此处可以return self，也可以return别的，来作为转场动画器；
3.写完上面的方法，发现要遵守协议
遵守完协议，发现有方法要实现
- (NSTimeInterval)transitionDuration:(nullableid)transitionContext{
return1;
}
- (void)animateTransition:(id)transitionContext{
UIView*containerView = [transitionContextcontainerView];
UIViewController*toVC = [transitionContextviewControllerForKey:UITransitionContextToViewControllerKey];
[containerViewaddSubview:toVC.view];
toVC.view.alpha=0;
[UIViewanimateWithDuration:[selftransitionDuration:transitionContext]animations:^{
toVC.view.alpha=1;
}completion:^(BOOLfinished) {
[transitionContextcompleteTransition:YES];
}];
}
上述两个方法，一个是给出动画执行的时间，第二个是动画具体执行的动作
之后就可以实现转场动画了。
