问题描述
我有一个 NSArray ，其中包含以下格式的日期/时间 NSStrings ：
I have an NSArray containing date/time NSStrings in the following format:
2/2/2011 2:46:39 PM
2/4/2011 11:59:47 AM
…
其中日期表示为月/日/年。
where the date is represented as month/day/year.
如何对NSArray进行排序以确保最新的日期/时间位于顶部？
How do I sort this NSArray making sure the newest date/times are at the top?
推荐答案
当你'处理日期，使用 NSDate 而不是 NSString 。此外，考虑时区很重要 - Web服务是否提供UTC或其他时区的日期？
When you’re dealing with dates, use NSDate instead of NSString. Also, it’s important to consider the time zone — does the Web service provide dates in UTC or some other time zone?
您应该首先将字符串数组转换为数组日期。否则，每当用于比较时，你都会将字符串转换为日期，并且会有比字符串数更多的比较。
You should first convert your array of strings into an array of dates. Otherwise, you’d be converting a string to a date whenever it is used for comparison, and there will be more comparisons than the number of strings.
例如：
NSDateFormatter *formatter = [[[NSDateFormatter alloc] init] autorelease];
[formatter setDateFormat:@"MM/DD/YYYY hh:mm:ss a"];
NSMutableArray *dateArray = [NSMutableArray array];
for (NSString *dateString in array) {
NSDate *date = [formatter dateFromString:dateString];
if (date) [dateArray addObject:date];
// If the date is nil, the string wasn't a valid date.
// You could add some error reporting in that case.
}
这会转换数组 ，一个 NSStrings 的数组，到 dateArray ，一个可变数组 NSDates 。日期格式化程序使用系统时区。如果您想使用UTC作为时区：
This converts array, an array of NSStrings, to dateArray, a mutable array of NSDates. The date formatter uses the system time zone. If you want to use UTC as the time zone:
NSDateFormatter *formatter = [[[NSDateFormatter alloc] init] autorelease];
[formatter setDateFormat:@"MM/DD/YYYY hh:mm:ss a"];
[formatter setTimeZone:[NSTimeZone timeZoneWithAbbreviation:@"UTC"]];
完成后，对数组进行排序非常简单：
Having done that, sorting the array is trivial:
[dateArray sortUsingSelector:@selector(compare:)];
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