将 NSString 转换为 NSDate 不起作用

Question

i use code same this best answer

Converting NSString to NSDate (and back again)

NSString *dateString = @"01-02-2010";
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
// this is imporant - we set our input date format to match our input string
// if format doesn't match you'll get nil from your string, so be careful
[dateFormatter setDateFormat:@"dd-MM-yyyy"];
NSDate *dateFromString = [[NSDate alloc] init];
// voila!
dateFromString = [dateFormatter dateFromString:dateString];

but dateFromString result is 2010-01-31 17:00:00 +0000 why it not same day.
i cannot compare date.

Answer 1

这是因为你当前的时区，添加这个然后它会给你正确的日期

[dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"GMT"]];

Answer 2

Add the following line right after where you have set the date format. It because it will convert by default with local timezone of the device. It works for me!

[dateFormatter setTimeZone:[NSTimeZone timeZoneWithName:@"UTC"]];

Answer 3

It is actually the same date. But the date formatter, by default, parses the date string in the local timezone of the device if a timezone is not passed in. In your case, your date was intepreted as Midnight February 2nd 2010 UTC+7 which is January 31st 2010 17:00 UTC.

If the date string is always in UTC, pass in the UTC timezone into the date formatter like this:

NSString *dateString = @"01-02-2010";
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setTimeZone:[NSTimeZone timeZoneWithAbbreviation:@"UTC"]];
// this is imporant - we set our input date format to match our input string
// if format doesn't match you'll get nil from your string, so be careful
[dateFormatter setDateFormat:@"dd-MM-yyyy"];
NSDate *dateFromString = [[NSDate alloc] init];
// voila!
dateFromString = [dateFormatter dateFromString:dateString];