选择器发送给类别中被覆盖的方法失败 [英] Selector Sent to method overridden in Category fails

问题描述

我正在尝试使用类别覆盖UIStoryboard方法。这是我的实现：

I am trying to override a UIStoryboard method using a category. Here is my implementation:

#import "UIStoryboard+SomeCategory.h"
#import <UIKit/UIKit.h>

@implementation UIStoryboard(SomeCategory)

-(id)instantiateInitialViewController
{
    NSLog(@"SUPER CLASS: %@", [super class]); // logs "UIStoryboard"
    NSLog(@"SUPER RTS  : %@", [super respondsToSelector:@selector(instantiateInitialViewController)] ? @"YES" : @"NO"); // logs "YES"
    return [super instantiateInitialViewController];
}

@end

当我添加时：

 UIViewController *viewController = [super instantiateInitialViewController]

为什么会出现编译器错误：

Why do I get the compiler error:

Receiver type 'NSObject' for instance message does not declare a method with selector 'instantiateViewController'

推荐答案

请注意， [超类] 与 [自身超类] 不同。引用文档：

You should note that [super class] is not the same as [self superclass]. Quoting the docs:

Objective-C提供了两个术语，可在方法定义中使用它们来引用执行该方法的对象，即self和super。

它们在编译器搜索方法实现的方式上有所不同，在某些情况下，它们的含义相同。

They differ in how the compiler will search for the method implementation, and in some cases they will mean just the same.

在这种情况下，您需要：

In this case you want:

NSLog(@"SUPER CLASS: %@", [self superclass]); // logs "NSObject"

检查对象的超类，您将需要一个UIStoryBoard子类，而不是类别，可以使用：

to check an object's super class class, and you'll need a UIStoryBoard subclass, not a category, to be able to use:

return [super instantiateInitialViewController];

为什么 [超类] 不记录您期望的另一主题。如果您有兴趣，则此帖子什么是是Objective-C中的元类？是一个很好的起点。

Why [super class] doesn't log what you expect is another subject. If you're interested, this post What is a meta-class in Objective-C? is a good starting point.

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