自定义返回键pop事件拦截

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-(void)WCSetUpNavItem{
    self.navigationItem.leftBarButtonItem = nil;//移除原有的统一定制的返回键
    UIButton *LeftItem = [UIButton buttonWithType:UIButtonTypeSystem];
    LeftItem.frame = CGRectMake(0, 0, 20, 20);
    [LeftItem setBackgroundImage:[UIImage imageNamed:@"nav_fanhui"] forState:UIControlStateNormal];
    [LeftItem addTarget:self action:@selector(BackBtnClick) forControlEvents:UIControlEventTouchUpInside];
    UIBarButtonItem *customLeftItem = [[UIBarButtonItem alloc] initWithCustomView:LeftItem];
    self.navigationItem.leftBarButtonItem = customLeftItem;
}

#pragma mark - 返回键点击
-(void)BackBtnClick{
  [UIAlertView alertWithCallBackBlock:^(NSInteger buttonIndex) {
      
  } title:@"提示" message:@"是否退出？" cancelButtonName:@"取消" otherButtonTitles:@"确定", nil];
}

实现拦截UIViewController的pop操作有两种方式：

自定义实现返回按钮，即设置UIBarButtonItem来实现自定义的返回操作。
创建UINavigatonController的Category，来定制navigationBar: shouldPopItem:的逻辑。

UIViewController+BackButtonHandler.h：

#import 

@protocol BackButtonHandlerProtocol 
@optional
// Override this method in UIViewController derived class to handle 'Back' button click
-(BOOL)navigationShouldPopOnBackButton;
@end

@interface UIViewController (BackButtonHandler) 

@end

UIViewController+BackButtonHandler.m：

#import "UIViewController+BackButtonHandler.h"

@implementation UIViewController (BackButtonHandler)

@end

@implementation UINavigationController (ShouldPopOnBackButton)

- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item {

    if([self.viewControllers count] < [navigationBar.items count]) {
        return YES;
    }

    BOOL shouldPop = YES;
    UIViewController* vc = [self topViewController];
    if([vc respondsToSelector:@selector(navigationShouldPopOnBackButton)]) {
        shouldPop = [vc navigationShouldPopOnBackButton];
    }

    if(shouldPop) {
        dispatch_async(dispatch_get_main_queue(), ^{
            [self popViewControllerAnimated:YES];
        });
    } else {
        // Workaround for iOS7.1. Thanks to @boliva - http://stackoverflow.com/posts/comments/34452906
        for(UIView *subview in [navigationBar subviews]) {
            if(0. < subview.alpha && subview.alpha < 1.) {
                [UIView animateWithDuration:.25 animations:^{
                    subview.alpha = 1.;
                }];
            }
        }
    }

    return NO;
}

使用：

在UIViewController当中引入头文件

#import "UIViewController+BackButtonHandler.h"

在UIViewController中实现navigationShouldPopOnBackButton方法。

- (BOOL)navigationShouldPopOnBackButton{
    [[[UIAlertView alloc] initWithTitle:@"提示" message:@"确定返回上一界面?"
                               delegate:self cancelButtonTitle:@"取消" otherButtonTitles:@"确定", nil] show];
    //renturn no 拦截pop事件
    return NO;
}

参考文献：
将navigationBar上的左边按钮移除
iOS拦截导航栏返回按钮事件的正确方式
UIViewController-BackButtonHandler