黑科技实现navigationController 返回按钮自定

navigationbar 的返回箭头自定义，这是很常见的场景。网上找了很多，有继承 navigationcontroller 然后(省略若干代码)，觉得不太好。也有定义UIViewController 类别，然后重新定义 leftbarButton 和对应滑动事件，也觉得有点麻烦。于是自己研究的实现方法，本人觉得挺满意，希望给大家参考。

效果如下：

示例代码详见：github:CustomNavigationControllerBack

#import "UIViewController+YILBack.h"
#import <objc/runtime.h>

@implementation UIViewController (YILBack)
+(void)load{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class class = [self class];
        swizzleBackMethod(class, @selector(viewDidLoad), @selector(app_viewDidLoad));
    });
}

void swizzleBackMethod(Class class,SEL originalSelector,SEL swizzledSelector){
    Method originalMethod = class_getInstanceMethod(class, originalSelector);
    Method swizzledMethod = class_getInstanceMethod(class, swizzledSelector);
    BOOL didAddMethod = class_addMethod(class, originalSelector, method_getImplementation(swizzledMethod), method_getTypeEncoding(swizzledMethod));
    if (didAddMethod) {
        class_replaceMethod(class, swizzledSelector, method_getImplementation(originalMethod), method_getTypeEncoding(originalMethod));
    }else{
        method_exchangeImplementations(originalMethod, swizzledMethod);
    }
}

- (void)app_viewDidLoad {
    [self app_viewDidLoad];
    [self customBackAppearance];
}
- (void)customBackAppearance {
        UIImage *backButtonBackgroundImage = [UIImage imageNamed:@"back"];
        backButtonBackgroundImage = [backButtonBackgroundImage resizableImageWithCapInsets:UIEdgeInsetsMake(0, backButtonBackgroundImage.size.width - 1, 0, 0)];
        id appearance = [UIBarButtonItem appearanceWhenContainedIn:[UINavigationController class], nil];
        [appearance setBackButtonBackgroundImage:backButtonBackgroundImage forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];
        UIBarButtonItem *backBarButton = [[UIBarButtonItem alloc] initWithTitle:self.title style:UIBarButtonItemStylePlain target:nil action:NULL];
        self.navigationItem.backBarButtonItem = backBarButton;
}

注：返回按钮图标请务必使用 40*40 或60*60
亲，觉得好久点个赞吧😝