比较两个 NSDates 的月份和日期

Question

I need to setup an if/else statement that compares only the month and day of two NSDates. One of the dates is selected with a UIDatePicker and the other would be today's date. If the month and date of the two are the same, something happens, if not something else happens.

This is how I currently have it set up, but it's not working (the else statement always fires). Not sure where to go from here:

.h

@interface ViewController : UIViewController {
    UIDatePicker *datePicker;
    NSDate *pickedDate;
    NSDateFormatter *pickedDateFormat;
    NSString *pickedDateString;
    NSDate *todaysDate;
    NSDateFormatter *todaysDateFormat;
    NSString *todaysDateString;
    UILabel *label;
}

.m

- (IBAction)buttonToCompareDates:(id)sender {
    // Sets date from date picker
    pickedDate = [datePicker date];
    pickedDateFormat = [[NSDateFormatter alloc] init];
    [pickedDateFormat setDateFormat:@"MM/dd"];
    pickedDateString = [pickedDateFormat stringFromDate:pickedDate];

    // Sets today's date
    todaysDate = [NSDate date];
    todaysDateFormat = [[NSDateFormatter alloc] init];
    [todaysDateFormat setDateFormat:@"MM/dd"];
    todaysDateString = [todaysDateFormat stringFromDate:todaysDate];

    // if/else statement 
    if (todaysDateString == pickedDateString) {
         label.text = @"The dates match.";
    } else { 
         label.text = @"The dates don't match.";
    }
}

I was under the assumption that this would work, but it doesn't. I only need to match the month and day sections of the NSDates, therefore I tried to format them down to those parts and compare the strings. Problem is, I always get the "The dates don't match." sentence, even when the dates do match. Not sure why, could use an explanation and the right way to go about this.

Answer 1

You have to use

if ([todaysDateString isEqualToString:pickedDateString]) {

instead of

if (todaysDateString == pickedDateString) {

Because you have to compare string contents instead of their pointers.

Also you can optimize you implementation by using the same Date Formatter:

- (IBAction)buttonToCompareDates:(id)sender {
    dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"MM/dd"];

    // Sets date from date picker
    pickedDate = [datePicker date];
    pickedDateString = [dateFormatter stringFromDate:pickedDate];

    // Sets today's date
    todaysDate = [NSDate date];
    todaysDateString = [dateFormatter stringFromDate:todaysDate];

    // if/else statement 
    if ([todaysDateString isEqualToString:pickedDateString]) {
         label.text = @"The dates match.";
    } else { 
         label.text = @"The dates don't match.";
    }
}

Answer 2

Comparing strings could work but it's probably more efficient to use NSCalendar like this:

NSDate *date1, *date2;
NSDateComponents* components1 = [[NSCalendar currentCalendar] components:NSMonthCalendarUnit|NSDayCalendarUnit fromDate:date1];
NSDateComponents* components2 = [[NSCalendar currentCalendar] components:NSMonthCalendarUnit|NSDayCalendarUnit fromDate:date2];
if (components1.month == components2.month && components1.day == components2.day) {
    // same month and day
} else {
    // not same month and day
}

Answer 3

now, since iOS 8+, it's like :

NSDateComponents* components1 = [[NSCalendar currentCalendar] components:NSCalendarUnitMonth|NSCalendarUnitDay fromDate:dateArticle];
NSDateComponents* components2 = [[NSCalendar currentCalendar] components:NSCalendarUnitMonth|NSCalendarUnitDay fromDate:frDateNow];

if (components1.month == components2.month && components1.day == components2.day) {
    // same month and day
} else {
    // not same month and day
}