Date Formatters　用法总结

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#date #output #string #styles #object #user

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本文详细介绍了如何使用Objective-C中的NSDateFormatter类进行日期格式化，并展示了如何使用不同样式呈现日期与时间，同时提供了自定义日期格式的方法及本地化日期显示的实现。

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Date Formatters

Use Formatter Styles to Present Dates and Times With the User’s Preferences

NSDateFormatterNoStyle 不显示

NSDateFormatterShortStyle　1/25/12 7:11 PM

NSDateFormatterMediumStyle　Jan 25, 2012 7:14:40 PM

NSDateFormatterLongStyle　January 25, 2012 7:15:28 PM GMT+08:00

NSDateFormatterFullStyle　Wednesday, January 25, 2012 7:16:34 PM China Standard Time

Listing 1  Formatting a date using formatter styles
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateStyle:NSDateFormatterMediumStyle];
[dateFormatter setTimeStyle:NSDateFormatterNoStyle];
 
NSDate *date = [NSDate dateWithTimeIntervalSinceReferenceDate:162000];
 
NSString *formattedDateString = [dateFormatter stringFromDate:date];
NSLog(@"formattedDateString: %@", formattedDateString);
// Output for locale en_US: "formattedDateString: Jan 2, 2001"

Use Format Strings to Specify Custom Formats　用格式化字符串来指定自定义格式

Fixed Formats

To specify a custom fixed format for a date formatter, you use setDateFormat:.

Note with the Unicode format string format, you should enclose literal text in the format string between apostrophes ('').

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:@"yyyy-MM-dd 'at' HH:mm"];
 
NSDate *date = [NSDate dateWithTimeIntervalSinceReferenceDate:162000];
 
NSString *formattedDateString = [dateFormatter stringFromDate:date];
NSLog(@"formattedDateString: %@", formattedDateString);
// For US English, the output may be:
// formattedDateString: 2001-01-02 at 13:00

Custom Formats for User-Visible Dates

使用本地时间

NSString *formatString = [NSDateFormatter dateFormatFromTemplate:@"EdMMM" options:0
                                          locale:[NSLocale currentLocale]];
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateFormat:formatString];
 
NSString *todayString = [dateFormatter stringFromDate:[NSDate date]];
NSLog(@"todayString: %@", todayString);

 Wed, Jan 25

使用异地时间

NSLocale *usLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US"];
NSString *usFormatString = [NSDateFormatter dateFormatFromTemplate:@"EdMMM" options:0 locale:usLocale];
NSLog(@"usFormatterString: %@", usFormatString);
// Output: usFormatterString: EEE, MMM d　　　Mon, Jan 3
 
NSLocale *gbLocale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_GB"];
NSString *gbFormatString = [NSDateFormatter dateFormatFromTemplate:@"EdMMM" options:0 locale:gbLocale];
NSLog(@"gbFormatterString: %@", gbFormatString);
// Output: gbFormatterString: EEE d MMM　　　　Mon 31 Jan

Formatters and User Interface Elements

１.直接从IB中拖拽Formatters到对象上，然后进行设置

２.用代码添加的方式

NSNumberFormatter *numberFormatter = [[NSNumberFormatter alloc] init];
[numberFormatter setNumberStyle:NSNumberFormatterCurrencyStyle];
[[textField cell] setFormatter:numberFormatter];

NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
[dateFormatter setDateStyle:NSDateFormatterMediumStyle];
[dateFormatter setTimeStyle:NSDateFormatterNoStyle];
[[contactsForm cells] makeObjectsPerformSelector:@selector(setFormatter:)
         withObject:dateFormatter]

When the cell needs to display or edit its value, it passes its object to the formatter which returns the formatted string. When the user enters a string, or when a string is programmatically written in a cell (usingsetStringValue), the cell obtains the corresponding object from the formatter.