UIViewController+BackButtonHandler是用來攔截系統(tǒng)導(dǎo)航欄返回事件舶衬，并提供方法來處理返回事件

UIViewController+BackButtonHandler.h

#import <UIKit/UIKit.h>

@protocol BackButtonHandlerProtocol <NSObject>
@optional
// 重寫下面的方法以攔截導(dǎo)航欄返回按鈕點擊事件系洛，返回 YES 則 pop蓉媳，NO 則不 pop
-(BOOL)navigationShouldPopOnBackButton;
@end

// 表示遵循這個代理
@interface UIViewController (BackButtonHandler) <BackButtonHandlerProtocol>

@end

UIViewController+BackButtonHandler.h是UIViewController的分類邮破，在.h里聲明一個代理方法

UIViewController+BackButtonHandler.m

#import "UIViewController+BackButtonHandler.h"

@implementation UIViewController (BackButtonHandler)

@end

@implementation UINavigationController (ShouldPopOnBackButton)//UINavigationController的分類

- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item {
    //判斷是否返回
    if([self.viewControllers count] < [navigationBar.items count]) {
        return YES;
    }
    
    BOOL shouldPop = YES;
    //獲取最上層的UIViewController
    UIViewController* vc = [self topViewController];
    //判斷是否有navigationShouldPopOnBackButton方法
    if([vc respondsToSelector:@selector(navigationShouldPopOnBackButton)]) {
        shouldPop = [vc navigationShouldPopOnBackButton];
    }
    
    if(shouldPop) {
        dispatch_async(dispatch_get_main_queue(), ^{
            [self popViewControllerAnimated:YES];
        });
    } else {
        // 取消 pop 后惜索，復(fù)原返回按鈕的狀態(tài)
        for(UIView *subview in [navigationBar subviews]) {
            if(0. < subview.alpha && subview.alpha < 1.) {
                [UIView animateWithDuration:.25 animations:^{
                    subview.alpha = 1.;
                }];
            }
        }
    }
    return NO;
}

@end

• (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item
  這個方法是導(dǎo)航欄將要返回時的方法征绸，方法中返回YES時克锣，導(dǎo)航欄將返回到上個界面赖晶，NO就不返回律适。這個方法需要注意的是，此方法不能在UIViewController中直接調(diào)用遏插，必須寫在創(chuàng)建的UINavigationController的地方捂贿。所以在UIViewController+BackButtonHandler.m創(chuàng)建了UINavigationController的分類@implementation UINavigationController (ShouldPopOnBackButton)

respondsToSelector方法是用來判斷是否有以某個名字命名的方法