Optimistic RegEx compliance for user text input

Question

I am working on a text application that uses regular expressions to validate user input. The goal is to allow keystrokes that match a specific RegEx and to reject invalid characters. One of the problems that I encountered is that when the user starts to enter information, he can create a string that does not match the given regular expression yet, but may lead to a match in the future. These lines are erroneously rejected. Here's an example - the following regular expression is set to enter date information:

(0?[1-9]|10|11|12)/(0?[1-9]|[12]\\d|30|31)/\\d{2}\\d{2}

The user can start typing "1 /", which may be a valid date, but RegEx.IsMatch()will return false, and my code will finish rejecting the line. Is there a way to “optimistically” test strings against a regular expression to allow possible or partial matches?

Bonus: for this RegEx, in particular, there are some sequences that cause the required characters. For example, if the user enters “2/15,” the only valid character that they can enter further is “/”. Can these scenarios be detected so that the necessary characters can be automatically entered for the user to facilitate input?

Answer 1

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^(0?[1-9]|10|11|12)(/((0?[1-9]|[12]\\d|30|31)(/(\\d{2}(\\d{2})?)?)?)?)?$

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Answer 2

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