iOS 字典类别（判断key是否存在）

一，先创建一个字典类别（这样字典可以直接调用，方法名不能与系统方法名重复）

-(id)takeOutKey:(NSString*)str{

  if ([[self allKeys]containsObject:str]){

    if ([[self objectForKey:str] isKindOfClass:[NSDictionary class]]) {

      return[selfobjectForKey:str];

    }else if ([[self objectForKey:str] isKindOfClass:[NSArray class]]){

      return[selfobjectForKey:str];

    }

    return [NSString stringWithFormat:@"%@",[self objectForKey:str]];

  }

  return @"";

}