Question

每当调用[managedObjectContext save:nil]时，我希望能够在NSManagedObject上执行自定义保存更改。

self.colorRaw = [NSKeyedArchiver archivedDataWithRootObject:self.color];

保存在此实现中。有什么想法吗？

@interface Filter : NSManagedObject
//auto-generated accessor
@property (nonatomic, retain) NSData * colorRaw;
// custom accessor
@property (strong, nonatomic) UIColor * color;

@end

@implementation
- (UIColor *)color
{
    UIColor * color;
    if ((color = objc_getAssociatedObject(self, @selector(color)))) {
        return color;
    }
    if (self.colorRaw.length) {
        color = [NSKeyedUnarchiver unarchiveObjectWithData:self.colorRaw];
        self.color = color;
        return color;
    }
    return nil;
}

- (void)setColor:(UIColor *)color
{
      objc_setAssociatedObject(self, @selector(color), color, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
} 
@end

Answer 1

答案其实很简单。只需为密钥NSManagedObjectContextWillSaveNotification

添加一个观察者

按照文档

[[NSNotificationCenter defaultCenter] addObserver:self
                                      selector:@selector(<#Selector name#>)
                                      name: NSManagedObjectContextWillSaveNotification
                                      object:<#A managed object context#>];

覆盖NSManagedObject保存

1 个答案: