Question

我在头文件中设置NSString *oldChat，如下所示：

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

@end

然后我用它：

- (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];
}

应用程序因if (![chat isEqual:oldChat])错误导致EXC_BAD_ACCESS崩溃。为什么它崩溃了？

（XCode 4.5.2，iPhone Simulator 6.0，Base SDK 6.0）

Answer 1

oldChat是autorelease个对象。保留它并使用isEqualToString进行字符串比较。

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

Answer 2

您必须使用isEqualToString：方法检查您的NSString是否相等。你的代码应该是这样的

if (![chat isEqualToString:oldChat]){
    //Do something
}

应用程序在后台崩溃与EXC_BAD_ACCESS

2 个答案: