在開發(fā)過程中，我們經(jīng)常遇到使用系統(tǒng)導(dǎo)航欄的功能，如何更改返回按鈕的樣式呢？

一、更改返回按鈕圖片

// 更換返回按鈕的圖片
UIImage *backButtonImage = [[UIImage imageNamed:@"bt_navigationBar_back"] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
    
[UINavigationBar appearance].backIndicatorTransitionMaskImage = backButtonImage;
[UINavigationBar appearance].backIndicatorImage = backButtonImage;


// 返回按鈕的文字置空（在UINavigationController的子類或者分類categary）中添加該方法
- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPushItem:(UINavigationItem *)item {
    UIBarButtonItem *back = [[UIBarButtonItem alloc] initWithTitle:@"" style:UIBarButtonItemStylePlain target:nil action:nil];
    item.backBarButtonItem = back;
    return YES;
}

二、重寫返回按鈕

重寫返回按鈕一般是添加leftBarButtonItems。如果導(dǎo)航欄添加了leftBarButtonItems之后，會(huì)自動(dòng)隱藏返回按鈕backBarButtonItem。

// 返回按鈕
UIBarButtonItem *backBarButtonItem = [[UIBarButtonItem alloc] initWithImage:[[UIImage imageNamed:@"bt_navigationBar_back"] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal] style:UIBarButtonItemStylePlain target:self action:@selector(backAction)];
self.navigationItem.leftBarButtonItem = backBarButtonItem;

// 返回按鈕的回調(diào)方法
- (void)backAction {
}

三、攔截系統(tǒng)導(dǎo)航欄的返回按鈕監(jiān)聽事件

當(dāng)我們使用了系統(tǒng)的導(dǎo)航欄時(shí)，默認(rèn)點(diǎn)擊返回按鈕是 pop 回上一個(gè)界面。但是在有時(shí)候，我們需要在點(diǎn)擊導(dǎo)航欄的返回按鈕時(shí)不一定要 pop 回上一界面，可能是其他的頁面，我們需要攔截返回按鈕的pop操作。

1、重寫返回按鈕
具體操作查看上面“二、重寫返回按鈕”。
缺點(diǎn)：若重寫了某個(gè)界面的返回按鈕，感覺應(yīng)用整體就不統(tǒng)一了。而且每有一個(gè)界面有這個(gè)需求都需要重新自定義一個(gè)返回按鈕，顯得不優(yōu)雅，工作繁瑣。

2、為 UINavigationController 添加 category

//item將要push的時(shí)候調(diào)用，返回NO，則不能push
- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPushItem:(UINavigationItem *)item; // called to push. return NO not to.

//item已經(jīng)push后調(diào)用
- (void)navigationBar:(UINavigationBar *)navigationBar didPushItem:(UINavigationItem *)item;    // called at end of animation of push or immediately if not animated

//item將要pop時(shí)調(diào)用，返回NO，不能pop  
- (BOOL)navigationBar:(UINavigationBar *)navigationBar shouldPopItem:(UINavigationItem *)item;  // same as push methods

//item已經(jīng)pop后調(diào)用 
- (void)navigationBar:(UINavigationBar *)navigationBar didPopItem:(UINavigationItem *)item;

我們可以為 UINavigatonController 創(chuàng)建一個(gè) Category，來定制navigationBar: shouldPopItem: 的邏輯。

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

@interface UIViewController (BackButtonHandler) <BackButtonHandlerProtocol>

@end

// UIViewController+BackButtonHandler.m 
@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，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;
}

使用時(shí)，只需要在需要攔截返回按鈕事件的控制器中，應(yīng)用#import "UIViewController+BackButtonHandler.h"，并重寫-(BOOL)navigationShouldPopOnBackButton方法即可。

- (BOOL)navigationShouldPopOnBackButton{
   //攔截返回按鈕后做的處理

    //返回NO（一定要返回NO）
    return NO;
}