NSDate 变成 NSNumber 之谜
我正在 iOS 4.3 & 中工作iOS 5 具有自动引用计数功能。我在界面中声明了一个 NSDate 对象：
NSDate *fingerprintsDate;
后来，我设置了 NSDate - 使用调试器并逐步执行它具有我期望的值：
fingerprintsDate = [NSDate date];
最后，我尝试从日期中获取时间：
if (fingerprintsDate == nil || [fingerprintsDate timeIntervalSinceNow] > 6)
这就是它因无法识别而崩溃的地方选择器：“2012-01-18 23:07:46.662 Netapporter[473:707] -[NSCFNumber timeIntervalSinceNow]：无法识别的选择器发送到实例 0x194490”
根据调试器，我亲爱的 NSDate 读到：“fingerprintsDate = (NSCFNumber *) 0x194490 139” - 当我打印描述时，它读到：“{value = +139.0000000000，type = kCFNumberFloat32Type}
”不做任何其他带有指纹的事情代码 - 但不知何故它变成了 NSNumer...有什么想法如何阻止它吗？
I'm working in iOS 4.3 & iOS 5 with automatic reference counting. I declare a NSDate object in my interface:
NSDate *fingerprintsDate;
Later, I set that NSDate - using the debugger and stepping through it has the value I'd expect:
fingerprintsDate = [NSDate date];
Finally, I try to get the time from the date:
if (fingerprintsDate == nil || [fingerprintsDate timeIntervalSinceNow] > 6)
And that's where it crashes with unrecognized selector: "2012-01-18 23:07:46.662 Netapporter[473:707] -[NSCFNumber timeIntervalSinceNow]: unrecognized selector sent to instance 0x194490"
According to the debugger, my dear NSDate reads: "fingerprintsDate = (NSCFNumber *) 0x194490 139" - when I print description it reads: "{value = +139.0000000000, type = kCFNumberFloat32Type}"
I'm not doing anything else w/ fingerprintsDate anywhere else in the code - but somehow it's turning into an NSNumer... Any ideas how to stop it?
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[NSDate date] 返回一个非保留值（如果您使用 arc，则为弱值），因此它很可能在该赋值和调用 [fingerprintsDate timeIntervalSinceNow] 之间的某个位置被释放。当您将其分配给保留（强）属性时，它就会被保留。
[NSDate date] returns a non-retained value (or weak if you're using arc), so it most likely got released somewhere between that assignment and calling [fingerprintsDate timeIntervalSinceNow]. When you assign it to a retained (strong) property, it's being retained.
你是用GBD调试，用GCC编译吗？可能与我的问题有关： -[NSDate timeIntervalSinceDate:] 在 GCC 4.2 上返回非常小的数字，但在 LLVM-GCC 4.2 上按预期工作在iOS4.3模拟器上
Are you debugging with GBD, compiling with GCC? Could be related to my question: -[NSDate timeIntervalSinceDate:] returns very small number on GCC 4.2, but works as expected on LLVM-GCC 4.2 on iOS4.3 Simulator