NSString的日期

NSString *dateString = [NSString stringWithFormat:@"%@",[NSDate date]];
NSLog(@"string: %@",dateString ); //2015-03-24 12:28:49 +0000

和陌生人约会

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss Z"];
NSDate *date = [formatter dateFromString:dateString];
NSLog(@"date: %@", date); //015-03-24 12:28:49 +0000

NSString *dateStr = @"Tue, 25 May 2010 12:53:58 +0000";

// Convert string to date object
NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:@"EE, d LLLL yyyy HH:mm:ss Z"];
NSDate *date = [dateFormat dateFromString:dateStr]; 
[dateFormat release];

为什么不给NSString添加一个category ?

// NSString+Date.h
@interface NSString (Date)
+ (NSDate*)stringDateFromString:(NSString*)string;
+ (NSString*)stringDateFromDate:(NSDate*)date;
@end


// NSString+Date.m
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc]init];
[dateFormatter setDateFormat:@"EEE, dd MMM yyyy HH:mm:ss ZZZ"];

NSDate *date = [dateFormatter dateFromString:stringDate ];
[dateFormatter release];
+ (NSDateFormatter*)stringDateFormatter
{
    static NSDateFormatter* formatter = nil;
    if (formatter == nil)
    {
        formatter = [[NSDateFormatter alloc] init];
        [formatter setDateFormat:@"EEE, dd MMM yyyy HH:mm:ss ZZZ"];
    }   
    return formatter;
}

+ (NSDate*)stringDateFromString:(NSString*)string
{
    return [[NSString stringDateFormatter] dateFromString:string];
}

+ (NSString*)stringDateFromDate:(NSDate*)date
{
    return [[NSString stringDateFormatter] stringFromDate:date];
}


// Usage (#import "NSString+Date.h") or add in "YOUR PROJECT".pch file
NSString* string = [NSString stringDateFromDate:[NSDate date]];
NSDate* date = [NSString stringDateFromString:string];

字符串到日期

var dateFormatter = DateFormatter()
dateFormatter.format = "dd/MM/yyyy"

var dateFromString: Date? = dateFormatter.date(from: dateString) //pass string here

日期到字符串

 var dateFormatter = DateFormatter()
 dateFormatter.dateFormat = "dd-MM-yyyy"
 let newDate = dateFormatter.string(from: date) //pass Date here

NSString的日期

NSString *dateString = [NSString stringWithFormat:@"%@",[NSDate date]];
NSLog(@"string: %@",dateString ); //2015-03-24 12:28:49 +0000

和陌生人约会

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"yyyy-MM-dd HH:mm:ss Z"];
NSDate *date = [formatter dateFromString:dateString];
NSLog(@"date: %@", date); //015-03-24 12:28:49 +0000

当使用固定格式的日期时，需要将日期格式化程序的区域设置为“en_US_POSIX”。

摘自数据格式化指南

If you're working with fixed-format dates, you should first set the locale of the date formatter to something appropriate for your fixed format. In most cases the best locale to choose is en_US_POSIX, a locale that's specifically designed to yield US English results regardless of both user and system preferences. en_US_POSIX is also invariant in time (if the US, at some point in the future, changes the way it formats dates, en_US will change to reflect the new behavior, but en_US_POSIX will not), and between platforms (en_US_POSIX works the same on iPhone OS as it does on OS X, and as it does on other platforms).

Swift 3或更高版本

extension Formatter {
    static let customDate: DateFormatter = {
        let formatter = DateFormatter()
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.dateFormat = "dd/MM/yy"
        return formatter
    }()
    static let time: DateFormatter = {
        let formatter = DateFormatter()
        formatter.locale = Locale(identifier: "en_US_POSIX")
        formatter.dateFormat = "HH:mm"
        return formatter
    }()
    static let weekdayName: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateFormat = "cccc"
        return formatter
    }()
    static let month: DateFormatter = {
        let formatter = DateFormatter()
        formatter.dateFormat = "LLLL"
        return formatter
    }()
}

extension Date {
    var customDate: String {
        return Formatter.customDate.string(from: self)
    }
    var customTime: String {
        return Formatter.time.string(from: self)
    }
    var weekdayName: String {
        return Formatter.weekdayName.string(from: self)
    }
    var monthName: String {
        return Formatter.month.string(from: self)
    }
}

extension String {
    var customDate: Date? {
        return Formatter.customDate.date(from: self)
    }
}

用法:

// this will be displayed like this regardless of the user and system preferences
Date().customTime          //  "16:50"
Date().customDate          //  "06/05/17"
// this will be displayed according to user and system preferences
Date().weekdayName         //  "Saturday"
Date().monthName           //  "May"

解析自定义日期并将日期转换回相同的字符串格式:

let dateString = "01/02/10"

if let date = dateString.customDate {
    print(date.customDate)   // "01/02/10\n"
    print(date.monthName)    // customDate
}

这里是你可以用来定制它的所有元素: