2 个 NSDate 应该相等不是吗？
我正在使用 Stig Brautaset(http://code.google.com/p/json-framework) 的 JSON 库，我需要序列化 NSDate。我正在考虑在将其 JSON化之前将其转换为字符串，但是，我遇到了这种奇怪的行为：
为什么这些 NSDates 不被认为是相等的？
NSDate *d = [[NSDate alloc] init];
NSDate *dd = [NSDate dateWithString:[d description]];
NSLog(@"%@", d);
NSLog(@"%@", dd);
if( [d isEqualToDate:dd] ){
NSLog(@"Yay!");
}
I'm using the JSON library from Stig Brautaset(http://code.google.com/p/json-framework) and I need to serialize an NSDate. I was considering converting it into a string before JSONifying it, however, I ran into this weird behavior:
Why aren't these NSDates considered equal?
NSDate *d = [[NSDate alloc] init];
NSDate *dd = [NSDate dateWithString:[d description]];
NSLog(@"%@", d);
NSLog(@"%@", dd);
if( [d isEqualToDate:dd] ){
NSLog(@"Yay!");
}
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当您描述原始日期对象时，您会失去原始对象的一些亚秒精度 - 换句话说，
-description剃须关闭小数秒，然后返回当您根据描述创建新的日期对象时，您会在整秒内获得它，因为该字符串仅精确到整秒。所以
-isEqualToDate:返回NO因为存在分数差异两个日期对象之间的一秒，它对此很敏感。所以你应该这样做（
NSTimeInterval以秒为单位）：When you describe the original date object you lose some sub-second precision from the original object — in other words,
-descriptionshaves off fractional seconds, and returnsWhen you create a new date object based on the description, you get it in whole seconds because the string is only precise to a whole second. So
-isEqualToDate:returnsNObecause there is a difference of a fraction of a second between your two date objects, which it's sensitive to.So you'd do something like this instead (
NSTimeIntervalmeasures in seconds):isEqualToDate 检测日期之间的亚秒差异，但描述方法不包括亚秒。
isEqualToDate detects subseconds differences between dates, but the description method does not include subseconds.
因为它们不等价：
产生：
换句话说，
+dateWithString:方法不保持亚秒精度。Because they're not equivalent:
Produces:
In other words, the
+dateWithString:method does not maintain sub-second precision.