如果我想添加键入的属性，是NSNotification子类化正确的路由？ [英] Is subclassing NSNotification the right route if I want to add typed properties?

问题描述

我试图子类化 NSNotification 。

Apple的文档 NSNotification 请注明以下内容：

Apple's docs for NSNotificationstate the following:

NSNotification 没有实例变量。因此，
必须子类化 NSNotification 并覆盖原始方法
name ， object 和 userInfo 。你可以选择你喜欢的任何指定的初始化程序
，但确保你的初始化程序不调用
NSNotification 的实现 init （通过 [super init] ）。
NSNotification 不是直接实例化，它的 init
方法引发异常。

NSNotification is a class cluster with no instance variables. As such, you must subclass NSNotification and override the primitive methods name, object, and userInfo. You can choose any designated initializer you like, but be sure that your initializer does not call NSNotification’s implementation of init (via [super init]). NSNotification is not meant to be instantiated directly, and its init method raises an exception.

但这对我并不清楚。是否应该创建这样的初始化程序？

But this isn't clear to me. Should I create an initializer like this?

-(id)initWithObject:(id)object
{
    return self;
}

推荐答案

子类 NSNotification 是一个非典型操作。我想我在过去几年里只看过它一次或两次。

Subclassing NSNotification is an atypical operation. I think I've only seen it done once or twice in the past few years.

如果你想与通知一起传递，那就是 userInfo 属性。如果您不喜欢直接通过 userInfo 访问内容，您可以使用类别来简化访问：

If you're looking to pass things along with the notification, that's what the userInfo property is for. If you don't like accessing things through the userInfo directly, you could use a category to simplify access:

@interface NSNotification (EasyAccess)

@property (nonatomic, readonly) NSString *foo;
@property (nonatomic, readonly) NSNumber *bar;

@end

@implementation NSNotification (EasyAccess)

- (NSString *)foo {
  return [[self userInfo] objectForKey:@"foo"];
}

- (NSNumber *)bar {
  return [[self userInfo] objectForKey:@"bar"];
}

@end

以简化 NSNotification 创建。例如，您的类别也可以包括：

You can also use this approach to simplify NSNotification creation. For example, your category could also include:

+ (id)myNotificationWithFoo:(NSString *)foo bar:(NSString *)bar object:(id)object {
  NSDictionary *d = [NSDictionary dictionaryWithObjectsForKeys:foo, @"foo", bar, @"bar", nil];
  return [self notificationWithName:@"MyNotification" object:object userInfo:d];
}

如果由于某种奇怪的原因， ，则您需要使用关联参考完成：

If, for some strange reason, you'd need the properties to be mutable, then you'd need to use associative references to accomplish that:

#import <objc/runtime.h>
static const char FooKey;
static const char BarKey;

...

- (NSString *)foo {
  return (NSString *)objc_getAssociatedObject(self, &FooKey);
}

- (void)setFoo:(NSString *)foo {
  objc_setAssociatedObject(self, &FooKey, foo, OBJC_ASSOCIATION_RETAIN);
}

- (NSNumber *)bar {
  return (NSNumber *)objc_getAssociatedObject(self, &BarKey);
}

- (void)setBar:(NSNumber *)bar {
  objc_setAssociatedObject(self, &BarKey, bar, OBJC_ASSOCIATION_RETAIN);
}

...

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