Iphone 实现类时出现Objective-C错误？

我有这门课

#import <Foundation/Foundation.h>

@interface SubscriptionArray : NSObject{
    NSString *title;
    NSString *source;
    NSString *htmlUrl;
}

@property (nonatomic,retain) NSString *title;
@property (nonatomic,retain) NSString *source;
@property (nonatomic,retain) NSString *htmlUrl;

@end

当我像本例中那样使用该类时，会出现EXEC\u BAD\u访问错误：

  for (NSDictionary *element in subs){
            SubscriptionArray *add;
            add.title=[element objectForKey:@"title"];   //ERROR Happens at this line
            add.source=[element objectForKey:@"htmlUrl"];
            add.htmlUrl=[element objectForKey:@"id"];
            [subscriptions addObject:add];


        }

有人能帮我吗？

---

P.S.订阅是一个NSMutableArray

您需要初始化订阅阵列。i、 e

SubscriptionArray *add = [SubscriptionArray new];

---

您需要像这样分配SubscriptionArray对象：

SubscriptionArray*add=[[SubscriptionArray alloc]init]

因此，for循环将如下所示：

for (NSDictionary *element in subs){
        SubscriptionArray *add = [[SubscriptionArray alloc] init];
        add.title=[element objectForKey:@"title"];
        add.source=[element objectForKey:@"htmlUrl"];
        add.htmlUrl=[element objectForKey:@"id"];
        [subscriptions addObject:add];
        [add release];
}

谢谢你的回答，我更正了我的代码，现在我得到了这个错误：2011-08-26 17:14:18.102 NewsPad[1204:15203]***由于未捕获的异常“NSInvalidArgumentException”而终止应用程序，原因：'-[\u NSCFSet objectAtIndex:]：未识别的选择器发送到实例0x7eb2cb0'这意味着什么？我能做什么？似乎您的元素变量引用的是NSSet而不是NSDictionary。要了解更多信息，我们需要查看定义SUB的代码在循环结束时，将
添加到
订阅后@paul@Josh是的，完全忘记了释放。已将其添加到代码中：）
for (NSDictionary *element in subs){
        SubscriptionArray *add = [[SubscriptionArray alloc] init];
        add.title=[element objectForKey:@"title"];
        add.source=[element objectForKey:@"htmlUrl"];
        add.htmlUrl=[element objectForKey:@"id"];
        [subscriptions addObject:add];
        [add release];
}