How do I monitor the fitting width change of an UIDatePicker on iOS using UIKit?

Question

I'd like to monitor the fitting width of an UIDatePicker set to the mode of .date on iOS. By fitting width, I mean that usually obtained by systemLayoutSizeFittingSize(CGSize(0, 0)) -- but I need to monitor its change and get the value of it after the change.

I know that it is possible to use UIControlEventValueChanged to monitor the change of the value which implies that its width would change... but I need to know its "preferred" width after the value of the Date Picker gets changed.

I am interested in knowing this because I am laying out the UIKit widgets using a custom algorithm, and it must know the width of the date picker. The date picker displays as a shaded rounded rectangle, so this is needed -- I don't think you can just "force" the date picker to another width.

EDIT: UIDatePicker seems to collapse into mm/dd/yyyy format when the width is set small. If that affects the fitting size, I'd like to monitor for the change of the intrinsic size.

A solution using a changed handler to force update of this value would be also welcome.

Why don't you just get its value and calculate the area needed to display it? — Leo Dabus
– Leo Dabus, Commented Jun 25 at 23:52
@LeoDabus But how? How am I supposed to know all the padding, etc? — John
– John, Commented Jun 25 at 23:57
That shouldn’t be too hard to figure out. Just start with the minimum needed to display the text and increase it as needed. — Leo Dabus
– Leo Dabus, Commented Jun 26 at 0:59
This question really needs a relevant portion of a screenshot or two better showing what it is you are trying to solve. Some relevant code would go a long way too. — HangarRash
– HangarRash, Commented Jun 27 at 22:46

John · Accepted Answer · 2025-09-05 22:42:37Z

1

In the on-change handler of whatever you're hooking up the UIDatePicker with, do this:

[datePicker setNeedsLayout];
[datePicker layoutIfNeeded];
CGFloat width = [datePicker systemLayoutSizeFittingSize:UILayoutFittingCompressedSize].width;

The first two lines are needed in order for it to be the latest size and not from before the change.

Reference: https://developer.apple.com/forums/thread/790220

edited Sep 5 at 22:42

answered Jul 4 at 0:44

John

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