Question

The following code displays an odd behavior under iOS 4.3 (maybe others version too). In this example, a UIDatePicker whose date is set to 4 Aug 2011 2:31 PM is displayed. The UILabel below the UIDatePicker displays the date for reference. The three UIButtons below, labeled 1, 5, 10 set the minuteInterval on the UIDatePicker.

Tapping 1 – shows the selected date in the UIDatePicker to be 4 Aug 2011 2:31 PM, and the minute interval is 1, which is to be expected.

Tapping 5 – shows the selected date in the UIDatePicker to be 4 Aug 2011 2:35 PM, and the minute interval is 5, which is to be expected (one could argue the time should round down, but that is not a huge issue).

Tapping 10 – shows the selected date in the UIDatePicker to be 4 Aug 2011 2:10 PM, and the minute interval is 10. Okay the minute interval is correct, but the selected time is 2:10? One would have expected 2:40 (if rounded up) or 2:30 (if rounded down).

BugDatePickerVC.h

#import <UIKit/UIKit.h>

@interface BugDatePickerVC : UIViewController {
    NSDateFormatter *dateFormatter;
    NSDate *date;
    UIDatePicker *datePicker;
    UILabel *dateL;
    UIButton *oneB;
    UIButton *fiveB;
    UIButton *tenB;
}

- (void) buttonEventTouchDown:(id)sender;

@end

BugDatePickerVC.m

import "BugDatePickerVC.h"

@implementation BugDatePickerVC

- (id) init
{
    if ( !(self = [super init]) )
    {
        return self;
    }

    dateFormatter = [[NSDateFormatter alloc] init];
    dateFormatter.dateFormat = @"d MMM yyyy h:mm a";

    date = [[dateFormatter dateFromString:@"4 Aug 2011 2:31 PM"] retain];

    // = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
    // Date picker
    datePicker = [[UIDatePicker alloc] initWithFrame:CGRectMake(0.0f, 0.0f, 320.0f, 216.0f)];
    datePicker.date = date;
    datePicker.minuteInterval = 1;
    [self.view addSubview:datePicker];

    // = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
    // Label with the date.
    dateL = [[UILabel alloc] initWithFrame:CGRectMake(10.0f, 230.0f, 300.0f, 32.0f)];
    dateL.text = [dateFormatter stringFromDate:date];
    [self.view addSubview:dateL];

    // = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
    // Button that set the date picker's minute interval to 1.
    oneB = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    oneB.frame = CGRectMake(10.0f, 270.0f, 100.0f, 32.0f);
    oneB.tag = 1;
    [oneB setTitle:@"1" forState:UIControlStateNormal];
    [oneB   addTarget:self
               action:@selector(buttonEventTouchDown:)
     forControlEvents:UIControlEventTouchDown];
    [self.view addSubview:oneB];

    // = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
    // Button that set the date picker's minute interval to 5.
    fiveB = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    fiveB.frame = CGRectMake(10.0f, 310.0f, 100.0f, 32.0f);
    fiveB.tag = 5;
    [fiveB setTitle:@"5" forState:UIControlStateNormal];
    [fiveB  addTarget:self
               action:@selector(buttonEventTouchDown:)
     forControlEvents:UIControlEventTouchDown];
    [self.view addSubview:fiveB];

    // = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
    // Button that set the date picker's minute interval to 10.
    tenB = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    tenB.frame = CGRectMake(10.0f, 350.0f, 100.0f, 32.0f);
    tenB.tag = 10;
    [tenB setTitle:@"10" forState:UIControlStateNormal];
    [tenB   addTarget:self
               action:@selector(buttonEventTouchDown:)
     forControlEvents:UIControlEventTouchDown];
    [self.view addSubview:tenB];

    return self;
}

- (void) dealloc
{
    [dateFormatter release];
    [date release];
    [datePicker release];
    [dateL release];
    [oneB release];
    [fiveB release];
    [tenB release];

    [super dealloc];
}

- (void) buttonEventTouchDown:(id)sender
{
    datePicker.minuteInterval = [sender tag];
}

Answer 1

Okay so I was able to change the behavior by explicitly setting the UIDatePicker date value to the date rounded to the minute interval using the following code:

- (void) handleUIControlEventTouchDown:(id)sender
{
    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    // Set the date picker's minute interval.
    NSInteger minuteInterval  = [sender tag];

    // Setting the date picker's minute interval can change what is selected on
    // the date picker's UI to a wrong date, it does not effect the date
    // picker's date value.
    //
    // For example the date picker's date value is 2:31 and then minute interval
    // is set to 10.  The date value is still 2:31, but 2:10 is selected on the
    // UI, not 2:40 (rounded up) or 2:30 (rounded down).
    //
    // The code that follow's setting the date picker's minute interval
    // addresses fixing the date value (and the selected date on the UI display)
    // .  In the example above both would be 2:30.
    datePicker.minuteInterval = minuteInterval;

    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    // Calculate the proper date value (and the date to be selected on the UI
    // display) by rounding down to the nearest minute interval.
    NSDateComponents *dateComponents = [[NSCalendar currentCalendar] components:NSMinuteCalendarUnit fromDate:date];
    NSInteger minutes = [dateComponents minute];
    NSInteger minutesRounded = ( (NSInteger)(minutes / minuteInterval) ) * minuteInterval;
    NSDate *roundedDate = [[NSDate alloc] initWithTimeInterval:60.0 * (minutesRounded - minutes) sinceDate:date];

    // - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
    // Set the date picker's value (and the selected date on the UI display) to
    // the rounded date.
    if ([roundedDate isEqualToDate:datePicker.date])
    {
        // We need to set the date picker's value to something different than
        // the rounded date, because the second call to set the date picker's
        // date with the same value is ignored. Which could be bad since the
        // call above to set the date picker's minute interval can leave the
        // date picker with the wrong selected date (the whole reason why we are
        // doing this).
        NSDate *diffrentDate = [[NSDate alloc] initWithTimeInterval:60 sinceDate:roundedDate];
        datePicker.date = diffrentDate;
        [diffrentDate release];
    }
    datePicker.date = roundedDate;
    [roundedDate release];
}

Pay attention to the part where the UIDatePicker‘s date is set twice. It was fun figuring that out.

Anyone know how to turn the animation off for the call to minuteInterval? The phantom scrolling when clicking 5 then 10 is a little unsightly.