objective-c - Finding an object in NSSet of different objects

Question

I have a NSSet that contains 3 different types of objects (FacebookGroup, Individual and NSMutableDictionary)

FacebookGroup and Individual are subclasses of NSManagedObject

Now I want to try to find an object matching key contactInfo so I do like this:

NSMutableDictionary *contactDict = [[self.contacts filteredSetUsingPredicate:[NSPredicate predicateWithFormat:@"contactInfo == %@", contactInfo]] anyObject];

if (contactDict) // the object is found

But FacebookGroups does not have the key contactInfo so an exception is throwed. I was hoping that instead an exception being throwed contactDict would be nil.

How can I search a NSSet of different objects without an exception being throwed?

* Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[ valueForUndefinedKey:]: the entity FacebookGroup is not key value coding-compliant for the key "contactInfo".'

Answer 1

如果您使用+ (NSPredicate *)predicateWithBlock:(BOOL (^)(id evaluatedObject, NSDictionary *bindings))blockthen 创建谓词，则可以在块中执行检查以确保evaluatedObject具有键，然后执行适当的检查。

Answer 2

您正在搜索的对象是NSMutableDictionary，这是从其他对象中识别它的方式，发送isKindOfClass消息。因此，您应该创建一个评估每个对象的谓词：

NSPredicate* predicate= [NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary *bindings) {
    return [evaluatedObject isKindOfClass: [NSMutableDictionary class]];
}];