作用：替换系统方法，便于在系统方法内书写自己的逻辑
方式：一般创建对应系统类的类别，然后在+load里写替换逻辑
注意点：慎用，别的地方会调用，可能会出现未知错误
在自己写的替换方法里要调用一次自己，保证系统方法原有逻辑的实现

eg: UIApplication中的workspace:willDestroyScene:withTransitionContext:completion:替换

+(void)load{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        Class _class = UIApplication.class;
        
        SEL _originSelector = @selector(workspace:willDestroyScene:withTransitionContext:completion:);
        SEL _newSelector = @selector(lzj_workspace:willDestroyScene:withTransitionContext:completion:);
        
        Method oriMethod = class_getInstanceMethod(_class, _originSelector);
        Method newMethod = class_getInstanceMethod(_class, _newSelector);
        if (!newMethod) {
            return;
        }
        
        BOOL isAddedMethod = class_addMethod(_class, _originSelector, method_getImplementation(newMethod), method_getTypeEncoding(newMethod));
        if (isAddedMethod) {
            // 如果 class_addMethod 成功了，说明之前 fromClass 里并不存在 originSelector，所以要用一个空的方法代替它，以避免 class_replaceMethod 后，后续 toClass 的这个方法被调用时可能会 crash
            IMP oriMethodIMP = method_getImplementation(oriMethod) ?: imp_implementationWithBlock(^(id selfObject) {});
            const char *oriMethodTypeEncoding = method_getTypeEncoding(oriMethod) ?: "v@:";
            class_replaceMethod(_class, _newSelector, oriMethodIMP, oriMethodTypeEncoding);
        } else {
            method_exchangeImplementations(oriMethod, newMethod);
        }
    });

}
- (void)lzj_workspace:(id)workspace willDestroyScene:(id)scene withTransitionContext:(id)context completion:(id)completion {
    [self lzj_workspace:workspace willDestroyScene:scene withTransitionContext:context completion:completion];
    NSLog(@"test");
    
}