objective-c - 覆盖子类的所有 setter 和 getter

Question

我想覆盖 setter 和 getter 并找到 objc_property_t 的类，而不是为每个属性单独执行它。

我得到了这样的所有属性:

unsigned int numberOfProperties;
    objc_property_t *propertyArray = class_copyPropertyList([self class], &numberOfProperties);
    for (NSUInteger i = 0; i < numberOfProperties; i++) {
        objc_property_t property = propertyArray[i];
        NSString *name = [[NSString alloc] initWithUTF8String:property_getName(property)];

        property.getter = SEL; //?
    }

这是我想如何覆盖 getter 和 setter 的示例 - 如果有更好的方法，请告诉我。也许是 NSInvocation？

- (UIImage *)backgroundImage
{
    return [self overrideGetterWithSelector:NSStringFromSelector(_cmd)];
}

- (void)setBackgroundImage:(UIImage *)backgroundImage
{
    [self overrideSetterForObject:backgroundImage forSelector:NSStringFromSelector(_cmd)];
}

或者有没有办法拦截发送给类的所有消息？

我的目标是制定一种通用方法来在两次启动之间存储类的属性。你可能想问为什么我不使用 NSUserDefaults 或 NSKeyedArchiver。好吧，我正在使用 NSKeyedArchiver - 我不想手动覆盖每一个 setter 和 getter。

Answer 1

您可以只使用来自 objc 运行时的 class_replaceMethod 来替换 getter 的实现。

例子:

- (void)replaceGetters {
    unsigned int numberOfProperties;
    objc_property_t *propertyArray = class_copyPropertyList([self class], &numberOfProperties);
    for (NSUInteger i = 0; i < numberOfProperties; i++) {
        objc_property_t property = propertyArray[i];
        const char *attrs = property_getAttributes(property);
        NSString *name = [[NSString alloc] initWithUTF8String:property_getName(property)];

        // property.getter = SEL; //?
        // becomes
        class_replaceMethod([self class], NSSelectorFromString(name), (IMP)myNewGetter, attrs);
    }
}

id myNewGetter(id self, SEL _cmd) {
    // do whatever you want with the variables....

    // you can work out the name of the variable using - NSStringFromSelector(_cmd)
    // or by looking at the attributes of the property with property_getAttributes(property);
    // There's a V_varName in the property attributes
    // and get it's value using - class_getInstanceVariable ()
    //     Ivar ivar = class_getInstanceVariable([SomeClass class], "_myVarName");
    //     return object_getIvar(self, ivar);
}