NSString *mystr=@"Your string date";

NSCalendar *cal = [NSCalendar currentCalendar];
NSDate *now = [dateFormatter dateFromString:mystr];

Nslog(@"%@",now);

如果你想设置格式使用下面的代码:

NSString *dateString = @"01-02-2010";
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];

// this is important - 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];
Nslog(@"%@",[dateFormatter dateFromString:dateString]);

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:

更新2019 (Swift 4):

为此做了一个日期扩展。它使用NSDataDetector而不是NSDateFormatter。

// Just throw at it without any format.
var date: Date? = Date.FromString("02-14-2019 17:05:05")

非常有趣，它甚至能识别像“明天5点”这样的东西。

XCTAssertEqual(Date.FromString("2019-02-14"),                    Date.FromCalendar(2019, 2, 14))
XCTAssertEqual(Date.FromString("2019.02.14"),                    Date.FromCalendar(2019, 2, 14))
XCTAssertEqual(Date.FromString("2019/02/14"),                    Date.FromCalendar(2019, 2, 14))
XCTAssertEqual(Date.FromString("2019 Feb 14"),                   Date.FromCalendar(2019, 2, 14))
XCTAssertEqual(Date.FromString("2019 Feb 14th"),                 Date.FromCalendar(2019, 2, 14))
XCTAssertEqual(Date.FromString("20190214"),                      Date.FromCalendar(2019, 2, 14))
XCTAssertEqual(Date.FromString("02-14-2019"),                    Date.FromCalendar(2019, 2, 14))
XCTAssertEqual(Date.FromString("02.14.2019 5:00 PM"),            Date.FromCalendar(2019, 2, 14, 17))
XCTAssertEqual(Date.FromString("02/14/2019 17:00"),              Date.FromCalendar(2019, 2, 14, 17))
XCTAssertEqual(Date.FromString("14 February 2019 at 5 hour"),    Date.FromCalendar(2019, 2, 14, 17))
XCTAssertEqual(Date.FromString("02-14-2019 17:05:05"),           Date.FromCalendar(2019, 2, 14, 17, 05, 05))
XCTAssertEqual(Date.FromString("17:05, 14 February 2019 (UTC)"), Date.FromCalendar(2019, 2, 14, 17, 05))
XCTAssertEqual(Date.FromString("02-14-2019 17:05:05 GMT"),       Date.FromCalendar(2019, 2, 14, 17, 05, 05))
XCTAssertEqual(Date.FromString("02-13-2019 Tomorrow"),           Date.FromCalendar(2019, 2, 14))
XCTAssertEqual(Date.FromString("2019 Feb 14th Tomorrow at 5"),   Date.FromCalendar(2019, 2, 14, 17))

就像:

extension Date
{


    public static func FromString(_ dateString: String) -> Date?
    {
        // Date detector.
        let detector = try! NSDataDetector(types: NSTextCheckingResult.CheckingType.date.rawValue)

        // Enumerate matches.
        var matchedDate: Date?
        var matchedTimeZone: TimeZone?
        detector.enumerateMatches(
            in: dateString,
            options: [],
            range: NSRange(location: 0, length: dateString.utf16.count),
            using:
            {
                (eachResult, _, _) in

                // Lookup matches.
                matchedDate = eachResult?.date
                matchedTimeZone = eachResult?.timeZone

                // Convert to GMT (!) if no timezone detected.
                if matchedTimeZone == nil, let detectedDate = matchedDate
                { matchedDate = Calendar.current.date(byAdding: .second, value: TimeZone.current.secondsFromGMT(), to: detectedDate)! }
        })

        // Result.
        return matchedDate
    }
}

2014年更新:

为此做了一个NSString扩展。

// Simple as this.   
date = dateString.dateValue;

多亏了NSDataDetector，它能识别很多格式。

'2014-01-16' dateValue is <2014-01-16 11:00:00 +0000>
'2014.01.16' dateValue is <2014-01-16 11:00:00 +0000>
'2014/01/16' dateValue is <2014-01-16 11:00:00 +0000>
'2014 Jan 16' dateValue is <2014-01-16 11:00:00 +0000>
'2014 Jan 16th' dateValue is <2014-01-16 11:00:00 +0000>
'20140116' dateValue is <2014-01-16 11:00:00 +0000>
'01-16-2014' dateValue is <2014-01-16 11:00:00 +0000>
'01.16.2014' dateValue is <2014-01-16 11:00:00 +0000>
'01/16/2014' dateValue is <2014-01-16 11:00:00 +0000>
'16 January 2014' dateValue is <2014-01-16 11:00:00 +0000>
'01-16-2014 17:05:05' dateValue is <2014-01-16 16:05:05 +0000>
'01-16-2014 T 17:05:05 UTC' dateValue is <2014-01-16 17:05:05 +0000>
'17:05, 1 January 2014 (UTC)' dateValue is <2014-01-01 16:05:00 +0000>

eppz的一部分!从GitHub获取类别NSString+EPPZKit.h。

2013年的原始答案:

无论您是否确定(或不关心)字符串中包含的日期格式，都可以使用NSDataDetector来解析日期。

//Role players.
NSString *dateString = @"Wed, 03 Jul 2013 02:16:02 -0700";
__block NSDate *detectedDate;

//Detect.
NSDataDetector *detector = [NSDataDetector dataDetectorWithTypes:NSTextCheckingAllTypes error:nil];
[detector enumerateMatchesInString:dateString
                           options:kNilOptions
                             range:NSMakeRange(0, [dateString length])
                        usingBlock:^(NSTextCheckingResult *result, NSMatchingFlags flags, BOOL *stop)
{ detectedDate = result.date; }];

首次约会还是第一次约会

//This method is used to get NSDate from string 
//Pass the date formate ex-"dd-MM-yyyy hh:mm a"
+ (NSDate*)getDateFromString:(NSString *)dateString withFormate:(NSString *)formate  {

    // Converted date from date string
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:@"en_US"]];
    [dateFormatter setDateFormat:formate];
    NSDate *convertedDate         = [dateFormatter dateFromString:dateString];
    return convertedDate;
}

//This method is used to get the NSString for NSDate
//Pass the date formate ex-"dd-MM-yyyy hh:mm a"
+ (NSString *)getDateStringFromDate:(NSDate *)date withFormate:(NSString *)formate {

    // Converted date from date string
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    //[dateFormatter setLocale:[[NSLocale alloc] initWithLocaleIdentifier:@"en_US"]];
    [dateFormatter setDateFormat:formate];
    NSString *convertedDate         = [dateFormatter stringFromDate:date];
    return convertedDate;
}

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

上面的例子不是简单地为Swift 3.0+编写的

更新- Swift 3.0+ -转换日期到字符串

let date = Date() // insert your date data here
var dateFormatter = DateFormatter()
dateFormatter.dateFormat = "yyyy-MM-dd" // add custom format if you'd like 
var dateString = dateFormatter.string(from: date)