获取所选时区的时间和日期? [英] Get the time and date of selected time zone?

问题描述

我尝试了下面的代码片段，我正在获取系统的当前日期和时间，而不是所选的时区代码.

I tried below snippet I'm getting current date and time of system instead of the selected time zone code.

NSDate *now = [NSDate date];
NSCalendar *gregorian=[[NSCalendar alloc] initWithCalendarIdentifier:NSGregorianCalendar];
[gregorian setTimeZone:[NSTimeZone timeZoneWithName:selectedzone]];

NSDateComponents* timeZoneComps = [gregorian components:NSYearCalendarUnit|NSMonthCalendarUnit|NSDayCalendarUnit|NSHourCalendarUnit|NSMinuteCalendarUnit|NSSecondCalendarUnit|NSTimeZoneCalendarUnit fromDate:now];

NSDate *selectedDate=[gregorian dateFromComponents:timeZoneComps];
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateStyle:NSDateFormatterFullStyle];
[formatter setDateFormat:@"dd-MM-yyyy HH:mm:ss "];
NSString *strSelectedDate= [formatter stringFromDate:selectedDate];
setZone.text = strSelectedDate;` 

有什么想法吗?

推荐答案

[NSDate date] 返回一个表示当前日期和时间的日期对象，无论您身在何处.NSDates 不受地点或时区的限制.只有一个 NSDate 代表现在或任何其他时刻，而不是每个时区的不同日期对象.因此，您不应尝试在时区之间转换日期.

[NSDate date]returns a date object representing the current date and time, no matter where you are. NSDates are not subject to places or time zones. There is just one NSDate that represents now or any other moment for that matter, not different date objects for every time timezone. Therefore, you should not attempt to convert a date between time zones.

NSDate objects represent an absolute instant in time. Consider the following example of how two date representations in different time zones (9/9/11 3:54 PM in Paris and 9/9/11 11:54 PM in Sydney) are actually the same date.
    NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
    [formatter setDateStyle:NSDateFormatterShortStyle];
    [formatter setTimeStyle:NSDateFormatterShortStyle];
    [formatter setTimeZone:[NSTimeZone timeZoneWithName:@"Europe/Paris"]];
    NSDate *aDate = [formatter dateFromString:@"9/9/11 3:54 PM"];
    [formatter setTimeZone:[NSTimeZone timeZoneWithName:@"Australia/Sydney"]];
    NSDate *anotherDate = [formatter dateFromString:@"9/9/11 11:54 PM"];
    NSLog(@"%@",anotherDate);
    if ([aDate isEqualToDate:anotherDate]) {
        NSLog(@"How about that?");
    }

在输出日期时，请记住，NSDate 的描述方法返回 GMT 时间，您需要使用 NSDateFormatter 从日期创建表示巴黎、悉尼等当地时间的日期字符串:

When it comes to output a date, bear in mind that NSDate's description method returns time in GMT and you need to use a NSDateFormatter to create a date string representing the local time in Paris, Sydney, etc. from a date:

NSDate *now = [NSDate date];
NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateStyle:NSDateFormatterShortStyle];
[formatter setTimeStyle:NSDateFormatterShortStyle];
[formatter setTimeZone:[NSTimeZone timeZoneWithName:@"Australia/Sydney"]];
NSLog(@"%@",[formatter stringFromDate:now]); //--> 9/9/11 11:54 PM
[formatter setTimeZone:[NSTimeZone timeZoneWithName:@"Europe/Paris"]];
NSLog(@"%@",[formatter stringFromDate:now]); //-->  9/9/11 3:54 PM

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