合并一个NSArray成的NSSet和避免对iphone在Objective-C复制

Question

编辑：更好的例子...

所以我有“现有”对象的的NSMutableSet，我想下载JSON数据，解析它，并将这些新对象与我现有的对象合并，使用新下载的对象更新任何重复对象。下面是现有的一组对象的样子：

NSArray *savedObjects = [NSArray arrayWithObjects: 
    [NSDictionary dictionaryWithObjectsAndKeys:@"1", @"id", @"hello there", @"body", @"200", @"score", nil], 
    [NSDictionary dictionaryWithObjectsAndKeys:@"2", @"id", @"hey now", @"body", @"10", @"score", nil], 
    [NSDictionary dictionaryWithObjectsAndKeys:@"3", @"id", @"welcome!", @"body", @"123", @"score", nil], 
    nil 
]; 
self.objects = [NSMutableSet setWithArray:savedObjects]; 

// after downloading and parsing JSON... I have an example array of objects like this: 

NSArray *newObjects = [NSArray arrayWithObjects: 
    [NSDictionary dictionaryWithObjectsAndKeys:@"1", @"id", @"hello there", @"body", @"9999", @"score", nil], 
    [NSDictionary dictionaryWithObjectsAndKeys:@"4", @"id", @"what's new", @"body", @"22", @"score", nil], 
    nil 
]; 

因此，例如，合并这个新的对象之后，ID为1的对象将现在的9999分和ID为4的新对象将被添加到集合。

我真的想避免循环每个新对象的NSMutableSet只是为了检查@“id”属性存在......我想我可以使用addObjectsFromArray来合并这些新的对象，但它看起来像是因为属性不同（例如：分数：9999）它不会将新对象看作集合中的现有对象。

我使用的数字作为字符串来简化这个例子。我也想避免使用仅适用于iOS SDK 4.0的功能，因为该应用将与3.0兼容。

谢谢！我很感激！

Answer 1

最好的办法是使用@“id”参数将第一组转换成字典。这里有一些代码应该做你想做的事情，它甚至可以处理没有@“id”参数的字典（在这一点上它们不会被合并，只包括在结果中）：

// here is the NSSet you already have 
self.objects = [NSSet setWithObjects: 
    [NSDictionary dictionaryWithObjectsAndKeys:@"1", @"id", @"hello there", @"body", @"200", @"score", nil], 
    [NSDictionary dictionaryWithObjectsAndKeys:@"2", @"id", @"hey now", @"body", @"10", @"score", nil], 
    [NSDictionary dictionaryWithObjectsAndKeys:@"3", @"id", @"welcome!", @"body", @"123", @"score", nil], 
    nil]; 

// after downloading and parsing JSON... I have an example array of objects like this: 

NSArray *newObjects = [NSArray arrayWithObjects: 
    [NSDictionary dictionaryWithObjectsAndKeys:@"1", @"id", @"hello there", @"body", @"9999", @"score", nil], 
    [NSDictionary dictionaryWithObjectsAndKeys:@"4", @"id", @"what's new", @"body", @"22", @"score", nil], 
    nil]; 

// Convert self.objects into a dictionary for merging purposes 
NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithCapacity:[self.objects count]]; 
NSMutableSet *remainder = [NSMutableSet set]; // for objects with no @"id" 
for (NSDictionary *obj in self.objects) { 
    NSString *objId = [obj objectForKey:@"id"]; 
    if (objId) { 
     [dict setObject:obj forKey:objId]; 
    } else { 
     [remainder addObject:obj]; 
    } 
} 

// merge the new objects in 
for (NSDictionary *obj in newObjects) { 
    NSString *objId = [obj objectForKey:@"id"]; 
    if (objId) { 
     // merge the new dict with the old 
     // if you don't want to merge the dict and just replace, 
     // simply comment out the next few lines 
     NSDictionary *oldObj = [dict objectForKey:objId]; 
     if (oldObj) { 
      NSMutableDictionary *newObj = [NSMutableDictionary dictionaryWithDictionary:oldObj]; 
      [newObj addEntriesFromDictionary:obj]; 
      obj = newObj; 
     } 
     // stop commenting here if you don't want the merging 
     [dict setObject:newObj forKey:objId]; 
    } else { 
     [remainder addObject:obj]; 
    } 
} 

// add the merged dicts back to the set 
[remainder addObjectsFromArray:[dict allValues]]; 
self.objects = remainder; 

Answer 2

不能完全确定从你的问题（因为本来应该使用它的一个iphone的问题，Objective C的符号），但它听起来像一个NSDictionary可能是你最好的朋友。

Answer 3

NSArray *array = ... // contains the new dictionary objects. 
NSMutableSet *set = ... // contains the existing set of dictionary objects. 

for (id arrayItem in array) 
{ 
    id setItem = [[set filteredSetUsingPredicate:[NSPredicate predicateWithFormat:@"id.intValue = %d", [[arrayItem valueForKey:@"id"] intValue]]] anyObject]; 
    if (setItem != nil) 
    { 
     [set removeObject:setItem]; 
     [set addObject:arrayItem]; 
    } 
}