iOS 拦截导航栏返回按钮事件(只拦截点击事件不改变系统按钮样式)

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#import <UIKit/UIKit.h>
@protocol BackButtonHandlerProtocol <NSObject>

@optional

/**
 重写下面的方法以拦截导航栏返回按钮点击事件，返回 YES 则 pop，NO 则不 pop

 @return <#return value description#>
 */
-(BOOL)navigationShouldPopOnBackButton;

@end


@interface UIViewController (BackButtonHandler)<BackButtonHandlerProtocol>

@end

#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
    {
        // 取消 pop 后，复原返回按钮的状态
        for(UIView *subview in [navigationBar subviews])
        {
            if(0.0 < subview.alpha && subview.alpha < 1.0)
            {
                [UIView animateWithDuration:0.25 animations:^{
                    subview.alpha = 1.0;
                }];
            }
        }
    }
    return NO;
}
@end

#import "UIViewController+BackButtonHandler.h"
//调用
- (BOOL)navigationShouldPopOnBackButton
{
    [[[UIAlertView alloc] initWithTitle:@"提示" message:@"确定退出吗？" delegate:self cancelButtonTitle:@"取消" otherButtonTitles:@"确定", nil] show];
    return NO;
}