键值观察-如何观察对象的所有属性?

问题描述

我对使用键值观察(KVO)以及如何注册以接收属性更改通知感到满意:

I am happy with the use of Key Value Observing (KVO), and how to register to receive notifications of property change:

[account addObserver:inspector
          forKeyPath:@"openingBalance"
             options:NSKeyValueObservingOptionNew
              context:NULL];

但是，如果我想观察帐户对象所有属性的变化，该如何实现?我必须注册每个属性的通知通知吗?

However, if I want to observe changes in all the properties of the account object, how can I achieve this? Do I have to register for notification for each and every property?

推荐答案

似乎没有内置函数可以订阅对象所有属性的更改.

It seems there's no built-in function to subscribe for changes in all properties of the objects.

如果您不关心确切地更改了哪个属性，并且可以更改您的类，则可以向其添加虚拟属性以观察其他属性的更改(使用+ keyPathsForValuesAffectingValueForKey或+keyPathsForValuesAffecting<Key>方法):

If you don't care about which exactly property has changed and can change your class you can add dummy property to it to observe changes in other properties (using + keyPathsForValuesAffectingValueForKey or +keyPathsForValuesAffecting<Key> method):

// .h. We don't care about the value of this property, it will be used only for KVO forwarding
@property (nonatomic) int dummy;

#import <objc/runtime.h>
//.m
+ (NSSet*) keyPathsForValuesAffectingDummy{

    NSMutableSet *result = [NSMutableSet set];

    unsigned int count;
    objc_property_t *props = class_copyPropertyList([self class], &count);

    for (int i = 0; i < count; ++i){
        const char *propName = property_getName(props[i]);
        // Make sure "dummy" property does not affect itself
        if (strcmp(propName, "dummy"))
            [result addObject:[NSString stringWithUTF8String:propName]];
    }

    free(props);
    return result;
}

现在，如果您观察dummy属性，则每次更改对象的任何属性时，都会收到KVO通知.

Now if you observe dummy property you'll get KVO notification each time any of object's properties is changed.

此外，您还可以像发布的代码中那样获取对象中所有属性的列表，并循环地为每个属性订阅KVO通知(这样就不必对属性值进行硬编码)-这样，您就可以如果需要，可以更改属性名称.

Also you can get list of all properties in the object as in the code posted and subscribe for KVO notifications for each of them in a loop (so you don't have to hard code property values) - this way you'll get changed property name if you need it.

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