Make a date field 'read-only' after that the date as been entered

Question

I have a form for my custom SharePoint List that, and I need to make a date field 'read-only' after someone goes in and fills in the date.

What is the best way to do to this via InfoPath?

Answer 1

Use Formatting rule.

If the date field is not blank and it has valid value, disable this field control (make it read-only).

In the InfoPath form, the date value always in this format:
yyyy-mm-ddThh:mm:ss
(e.g. 2019-03-05T00:00:00-07:00 or 2001-03-05T00:00:00)

Using the following pattern to check if the date value is valid:

((([0-9][0-9])|([1-2][0-9][0-9][0-9]))-(([1-9])|(0[1-9])|(1[0-2]))-(([0-9])|([0-2][0-9])|(3[0-1]))T00:00:00)|((([0-9][0-9])|([1-2][0-9][0-9][0-9]))-(([1-9])|(0[1-9])|(1[0-2]))-(([0-9])|([0-2][0-9])|(3[0-1]))T00:00:00-0([0-9]):00)

Use the rule: