iPhone OS: How do I create an NSDate for a specifi

问题:

Seems like a simple thing but I can't seem to find a way to do it.

It would be great to see a couple different methods.

回答1:

@Chuck's answer is correct, and lead me to the following code. Thought I'd share:

NSDateComponents *comps = [[NSDateComponents alloc] init];
[comps setDay:10];
[comps setMonth:10];
[comps setYear:2010];
NSDate *date = [[NSCalendar currentCalendar] dateFromComponents:comps];

回答2:

You can use this

NSString *dateString = @"03-Sep-11";
NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
dateFormatter.dateFormat = @"dd-MMM-yy";
NSDate *date = [dateFormatter dateFromString:dateString];

Hope this will help you out.

回答3:

If you're talking about a specific calendar date rather than a UNIXy date, you probably want NSCalendar's dateFromComponents:.

回答4:

Swift Examples

Examples are often the easiest way to learn. Here are a few examples.

Now

This one is the easiest.

let currentDateTime = Date()

February 20, 2017

// Specify date components
var dateComponents = DateComponents()
dateComponents.year = 2017
dateComponents.month = 2
dateComponents.day = 20

// Create date from components
let userCalendar = Calendar.current // user calendar
let dateThisPostWasUpdated = userCalendar.date(from: dateComponents)

April 1, 1976

// Specify date components
var dateComponents = DateComponents()
dateComponents.year = 1976
dateComponents.month = 4
dateComponents.day = 1

// Create date from components
let userCalendar = Calendar.current // user calendar
let appleFoundedDate = userCalendar.date(from: dateComponents)

Need more details...?

There are other ways to create dates, too. If you want to learn those, as well as how to display a date, then see my fuller answer.

回答5:

See the documentation for NSDate. You can use the dateFromString: method of NSDateFormatter or the dateFromComponents: method of NSCalendar.

回答6:

I found this thread while looking for an answer to this question but then I found a good example in one my Big Nerd Ranch Objective-C Programming book. Credit to them, not me.

  NSDateComponents *myBDay  =[[NSDateComponents alloc] init];
    [myBDay setDay:22];
    [myBDay setMonth: 04];
    [myBDay setYear: 1984];
    [myBDay setHour:9];
    [myBDay setMinute:25];
    [myBDay setSecond:35];

    NSCalendar *g = [[ NSCalendar alloc] initWithCalendarIdentifier:NSCalendarIdentifierGregorian];
    NSDate *dateOfBirth = [g dateFromComponents:myBDay];

回答7:

It is ridiculous, isn't it ?

Mid-2013 and Apple still hasn't provided a simple way to set a NSDate value.

During my current iPad project, I couldn't believe I had to stop productivity for a while to write my own helper class to get the Year value from an NSDate. I mean, come on, this is basic stuff.

Anyway, here's the helper class I used in my project, to convert a string into an NSDate value :

@implementation DateHelper

+(NSDate*)parseDateString:(NSString *)dateString
{
    NSDateFormatter *rfc3339TimestampFormatterWithTimeZone = [[NSDateFormatter alloc] init];
    [rfc3339TimestampFormatterWithTimeZone setLocale:[[NSLocale alloc] initWithLocaleIdentifier:@"en_US_POSIX"]];
    [rfc3339TimestampFormatterWithTimeZone setDateFormat:@"MMM dd, yyyy"];

    NSDate *theDate = nil;
    NSError *error = nil;
    if (![rfc3339TimestampFormatterWithTimeZone getObjectValue:&theDate forString:dateString range:nil error:&error]) {
        NSLog(@"Date '%@' could not be parsed: %@", dateString, error);
    }

    return theDate;
}

@end

Using this code, you could set an NSDate value using something like:

NSDate* date = [DateHelper parseDateString:@"Jul 16, 2013"];

Note: this function was based on code taken from here: https://stackoverflow.com/a/3968411/391605

My solution had been to use the following code, but I found that sometimes, it just wouldn't parse, and would return nil.

//  Take a date string in the format "Oct 23, 2013", and convert it into a NSDate value
//  THIS DOESN'T WORK !  DON'T TRUST THIS CODE !!
NSDateFormatter* formatter = [[NSDateFormatter alloc] init];
[formatter setDateFormat:@"MMM dd, yyyy"];
[formatter setTimeZone:[NSTimeZone timeZoneForSecondsFromGMT:0]];

NSDate* date = [formatter dateFromString:dateString];

I remember it failed miserably on "Oct 12, 2012"... which is why I gave up and used the more complicated "parseDateString" function shown above.

My point is... be careful.

Some of the very-basic NSDate functions just don't work properly...