Provide a default value for the time part.

[javier-godoy]

In order to update the time value when the user changes the date (for instance, set the time part automatically to 00:00)
one cannot rely on the change event of the component (since no event will be fired until both date and time are set).

As a workaround, one needs to add a change listener to dateSlot:

 dateTimePicker.$.dateSlot.children[0].addEventListener('change', function(){this.$.timeSlot.children[0].value='00:00';}.bind(dateTimePicker));

[TatuLund]

I could not get the JavaScript provided by @javier-godoy to work, perhaps there has been change in the component, but the example below works

      DateTimePicker picker = new DateTimePicker();
     
      picker.getElement().executeJs("this.getElementsByTagName(\"vaadin-date-time-picker-date-picker\")[0].addEventListener('change', function(){this.getElementsByTagName(\"vaadin-date-time-picker-time-picker\")[0].value='00:00';}.bind(this));");
      picker.addValueChangeListener(event -> {      
      Notification.show(event.getValue().toString());
      });
      add(picker);

[drewharvey]

Building off of @TatuLund 's workaround, you can modify it so that it only sets the time if it is not already set:

DateTimePicker picker = new DateTimePicker();

picker.getElement().executeJs(
        "this.getElementsByTagName(\"vaadin-date-time-picker-date-picker\")[0].addEventListener('change', function(){" +
                "if (!this.getElementsByTagName(\"vaadin-date-time-picker-time-picker\")[0].value) this.getElementsByTagName(\"vaadin-date-time-picker-time-picker\")[0].value='00:00';" +
        "}.bind(this));"
);
        
picker.addValueChangeListener(event -> Notification.show(event.getValue().toString()));
add(picker);

[muhammetkurt]

Is this ticket still in progress? I had the same issue and solved it with @TatuLund's workaround.

[archiecobbs]

The JS workaround doesn't seem to work for me (23.3.8) but I could be doing it wrong or something.

I ended up just forcing the initial value of the time picker to '00:00' from the Java side:

public class MyDateTimePicker extends DateTimePicker {

    private static final Field TIME_PICKER_FIELD;
    static {
        try {
            TIME_PICKER_FIELD = DateTimePicker.class.getDeclaredField("timePicker");
            TIME_PICKER_FIELD.setAccessible(true);
        } catch (NoSuchFieldException e) {
            throw new RuntimeException("unexpected error", e);
        }
    }

    public MyDateTimePicker() {
        timePicker.setValue(LocalTime.MIDNIGHT);    // work around #668
    }
}

[TatuLund]

In Vaadin 23/24 the JavaScript workaround is

    dateTime.getElement().executeJs("this.__datePicker.addEventListener('change', function(){this.__timePicker.value='00:00';}.bind(this));");