问题

UINavigationController顶部的返回按钮在切换视图时有左右滑动的动画(效果见iMail)，但在自定义了这个按钮后(通过设self.navigationItem.leftBarButtonItem自定义)，切换视图时按钮没有了动画。

最初解决方法

在每个viewController的viewWillAppear和viewDisappear方法上手动让按钮左右动。由于每个视图出现/消失的方向都有左/右两种，在这里难以判断，需要各种变量辅助，实现十分恶心，中间需要新加view时逻辑还要重新修改，被折腾。

最终解决方法

继承UINavigationController，重写pushViewController和popViewController方法，在这两个方法里面获取NavigationController里的view栈，因为push和pop总是操作最前面的View，所以可以从栈里知道哪两个view是要做动画的。调用这些view相应的方法使他们让自己的按钮动。这些方法可以写在UIViewController的扩展里，不用修改每一个viewController。

换言之，把下面的代码加入项目里，把项目里的UINavigationController换成下面的类，那些自定义的返回按钮就会自动做动画了。

代码

http://github.com/bang590/iOSPlayground/tree/master/NavigationButtonAnimate

//.h
#import <Foundation/Foundation.h>
@interface MainNavigationController : UINavigationController {
}
@end
//.m
#import "MainNavigationController.h"
@implementation UIViewController (UINavigationButtonAnimate)
- (void) viewAppearFromLeft
{
	[self.navigationItem.leftBarButtonItem.customView setTransform:CGAffineTransformMakeTranslation(-60, 0)];
	[UIView beginAnimations:@"viewAppearFromLeft" context:nil];
	[UIView setAnimationDuration:0.3];
	[self.navigationItem.leftBarButtonItem.customView setAlpha:1.0];
	[self.navigationItem.leftBarButtonItem.customView setTransform:CGAffineTransformMakeTranslation(0, 0)];
	[UIView commitAnimations];
}
- (void) viewAppearFromRight
{
	[self.navigationItem.leftBarButtonItem.customView setTransform:CGAffineTransformMakeTranslation(60, 0)];
	[UIView beginAnimations:@"viewAppearFromRight" context:nil];
	[UIView setAnimationDuration:0.3];
	[self.navigationItem.leftBarButtonItem.customView setAlpha:1.0];
	[self.navigationItem.leftBarButtonItem.customView setTransform:CGAffineTransformMakeTranslation(0, 0)];
	[UIView commitAnimations];
}
- (void) viewDisappearFromLeft
{
	[UIView beginAnimations:@"viewDisappearFromLeft" context:nil];
	[self.navigationItem.leftBarButtonItem.customView setTransform:CGAffineTransformMakeTranslation(60, 0)];
	[UIView setAnimationDuration:0.3];
	[self.navigationItem.leftBarButtonItem.customView setAlpha:0];
	[UIView commitAnimations];
}
- (void) viewDisappearFromRight
{
	[UIView beginAnimations:@"viewDisappearFromRight" context:nil];
	[self.navigationItem.leftBarButtonItem.customView setTransform:CGAffineTransformMakeTranslation(-60, 0)];
	[UIView setAnimationDuration:0.3];
	[self.navigationItem.leftBarButtonItem.customView setAlpha:0];
	[UIView commitAnimations];
}
@end
@implementation MainNavigationController
- (UIViewController *)popViewControllerAnimated:(BOOL)animated
{
	if (animated) {
		UIViewController *popController = [self.viewControllers lastObject];
		UIViewController *pushController = [self.viewControllers objectAtIndex:self.viewControllers.count - 2];
		[popController viewDisappearFromLeft];
		[pushController viewAppearFromLeft];
	}
	return [super popViewControllerAnimated:animated];
}
- (void)pushViewController:(UIViewController *)viewController animated:(BOOL)animated
{
	if (animated) {
		UIViewController *popController = [self.viewControllers lastObject];
		UIViewController *pushController = viewController;
		[popController viewDisappearFromRight];
		[pushController viewAppearFromRight];
	}
	[super pushViewController:viewController animated:animated];
}
@end