应用崩溃：EXC_BAD_ACCESS

在头文件中设置NSString *oldChat如下：

@interface CTFChatViewController : UIViewController {
    NSString *oldChat;
}
- (void)updateChat;
@property (nonatomic, retain) NSString *oldChat;

@end

然后使用：

- (void)updateChat
{
    NSString *chat = [NSString stringWithContentsOfURL:[NSURL URLWithString:@"http://theshay.byethost7.com/chat.php"] encoding:NSUTF8StringEncoding error:nil];
    if (![chat isEqual:oldChat]) 
    {
        [webView loadHTMLString:chat baseURL:nil];
        oldChat = chat;
    }

    [self performSelectorInBackground:@selector(updateChat) withObject:nil];
}

- (void)viewDidLoad
{
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.

    NSString *chat = [NSString stringWithContentsOfURL:[NSURL URLWithString:@"http://theshay.byethost7.com/chat.php"] encoding:NSUTF8StringEncoding error:nil];
    oldChat = chat;
    [webView loadHTMLString:chat baseURL:nil];

    [self performSelectorInBackground:@selector(updateChat) withObject:nil];
}

结果应用在if (![chat isEqual:oldChat])处出现了EXC_BAD_ACCESS错误。

怎么办？

使用版本：XCode 4.5.2，iPhone Simulator 6.0，Base SDK 6.0

控制台中没有输出异常原因么
楼主可以试试添加一个异常断点