Question

我有一些应该返回NSString的代码。相反，它有时返回NSArrayReverseEnumerator。这会导致无法识别的选择器发送到实例异常。

NSString *tFirstName = nil;
NSString *tUsername = ((NSString*)[self.userObject objectForKey:USER_NAME]).length > 0 ? [self.userObject objectForKey:USER_NAME] : [self.userObject objectForKey:USER_USERNAME];
NSRange spaceRange = [tUsername rangeOfString:@" "];
if (spaceRange.location == NSNotFound) {
    tFirstName = tUsername;
} else {
    tFirstName = [tUsername substringToIndex:spaceRange.location];
}
return tFirstName;

然后我将UITextField文本属性设置为导致异常的返回内容。

例外是：

- [__ NSArrayReverseEnumerator isEqualToString：]：无法识别的选择器发送到实例0xf1b8190

以下是堆栈跟踪的最后几行：

 CoreFoundation 0x381208bf __exceptionPreprocess + 163
1 libobjc.A.dylib 0x31c061e5 objc_exception_throw + 33
2 CoreFoundation 0x38123acb -[NSObject doesNotRecognizeSelector:] + 175
3 CoreFoundation 0x38122945 ___forwarding___ + 301
4 CoreFoundation 0x3807d680 _CF_forwarding_prep_0 + 48
5 UIKit 0x354dc20d -[UILabel setText:] + 45
6 Trivial 0x000873c9 -[vcGameOver viewDidLoad] (vcGameOver.m:45)
7 UIKit 0x355117ff -[UIViewController view] + 167

userObject通常看起来像这样，在调试器中还没有能够再现，看看它在异常时的样子：

userObject如下所示：

(PFUser *) $1 = 0x0be86fb0 <PFUser:MTsJR1DKuS> {
    answeredCorrect = "<PFRelation: 0xa847f30>";
    centsEarned = "-2353";
    centsPaidFor = 5000;
    centsUsed = 4193;
    correctAnswers = 1454;
    earnedCoinDate = "2012-06-12 19:42:44 +0000";
    eloRating = 1262;
    iq = 119;
    lastPlayedDate = "2012-06-12 19:15:46 +0000";
    locale = en;
    losses = 10;
    name = "Matt Hudson";
    status = 0;
    username = Inturbidus;
    wins = 8;
    wrongAnswers = 1157;
}

我的问题是，上面代码中的哪一行可以返回NSArrayReverseEnumerator？

Answer 1

你可能有一个悬空指针，还有一些其他物体（在这种情况下，可能是私人到苹果__NSArrayReverseEnumerator）蹲在记忆中的位置你的过早发布的NSString实例曾经是。

我建议打开僵尸（NSZombieEnabled）并查看是否收到“message sent to deallocated instance”错误消息而不是你得到的消息。

对象返回NSArrayReverseEnumerator。导致无法识别的选择器发送到实例

1 个答案: