iOS 自定义导航栏返回按钮

原文地址
参考1：关于backBarButtonItem的N种方法
参考2：How to make custom UINavigationController back button image without title

需求

项目中经常需要自定义导航栏返回按钮，只显示文字或者图片

分析

自定义导航栏返回按钮的思路很多：

1. 每个子视图控制器中修改 leftBarButtonItem 的样式，缺点是重复工作量大，如有变更不易修改。
2. 基类中通过实现 UINavigationController 的代理判断是否是栈底，如果不是栈底，则修改 leftBarButtonItem 的样式。
3. 在基类中设置backBarButtonItem，易于修改，工作量小。
4. Method Swizzling：将系统自带的backBarButtonItem方法替换成我们自定义的方法。

实现

方法2：

- (void)navigationController:(UINavigationController *)navigationController willShowViewController:(UIViewController *)viewController animated:(BOOL)animated
{
    UIViewController *root = navigationController.viewControllers[0];

    if (root != viewController) {
        UIBarButtonItem *itemleft = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"backBtn"] style:UIBarButtonItemStylePlain target:self action:@selector(popAction:)];
        viewController.navigationItem.leftBarButtonItem = itemleft;
    }
}


- (void)popAction:(UIBarButtonItem *)barButtonItem
{
    [self.navigationController popViewControllerAnimated:YES];
}

方法3：

     //只显示文字
    //self.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc] initWithTitle:@"返回" style:UIBarButtonItemStylePlain target:nil action:nil];

    //只显示图片
    self.navigationItem.backBarButtonItem = [[UIBarButtonItem alloc] initWithImage:[[UIImage imageNamed:@"nav_back"] imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal] style:UIBarButtonItemStylePlain target:nil action:nil];

    //更改返回按钮填充颜色
   //self.navigationController.navigationBar.tintColor = [UIColor darkGrayColor];

    //隐藏默认的返回箭头
    self.navigationController.navigationBar.backIndicatorImage = [UIImage new];
    self.navigationController.navigationBar.backIndicatorTransitionMaskImage = [UIImage new];

方法4：

+(void)load{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Method originalMethodImp = class_getInstanceMethod(self, @selector(backBarButtonItem));
        Method destMethodImp = class_getInstanceMethod(self, @selector(myCustomBackButton));
        method_exchangeImplementations(originalMethodImp, destMethodImp);
    });
}

static char kCustomBackButtonKey;

-(UIBarButtonItem *)myCustomBackButton{
    UIBarButtonItem *item = [self myCustomBackButton];
    if (item) {
        return item;
    }
    item = objc_getAssociatedObject(self, &kCustomBackButtonKey);
    if (!item) {
        item = [[UIBarButtonItem alloc] initWithTitle:@"返回" style:UIBarButtonItemStylePlain target:nil action:NULL];
        objc_setAssociatedObject(self, &kCustomBackButtonKey, item, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    return item;
}

- (void)dealloc
{
    objc_removeAssociatedObjects(self);
}