我承认，这不是***的，给它一个镜头，也许可以改进：

I'll admit, it's not the best, but give it a shot, maybe it can be improved:

在 viewDidLoad

[birthdayPicker addTarget:self
                   action:@selector(pickerValueChanged:)
         forControlEvents:UIControlEventValueChanged];

代码中的其他地方

- (IBAction)pickerValueChanged:(id)sender {
    dispatch_async(dispatch_get_main_queue(), ^{
        UIDatePicker *datePicker = (UIDatePicker *)sender;
        if ([datePicker.date compare:datePicker.maximumDate] == NSOrderedDescending) {
            datePicker.date = datePicker.maximumDate;
        }
        else if ([datePicker.date compare:datePicker.minimumDate] == NSOrderedAscending) {
            datePicker.date = datePicker.minimumDate;
        }

    });
}