Flutter how to validate password input field with regex

Question

I use regex validation in my custom textfield listener, to check if password valid

this is my validation code

 RegExp regexUpper = RegExp(r'^(?=.*[A-Z])$'); RegExp regexLower = RegExp(r'^(?=.*[a-z])$'); RegExp regexLength = RegExp(r'^.{8,}$'); if (!regexLength.hasMatch(value.toString())) { return 'Пароль слишком короткий'; } if (!regexLower.hasMatch(value.toString())) { print(value); return 'Пароль должен содержать хотя бы одну маленькую букву'; } if (!regexUpper.hasMatch(value.toString())) { return 'Введите хотя бы одну заглавную букву'; } return null;

regexLength work correctly but other not.

What i did wrong and how i can fix it ?

Take a look at this: stackoverflow.com/questions/16800540/… — user18309290
– user18309290, Commented Jun 15, 2022 at 14:42

Wiktor Stribiżew · Accepted Answer · 2022-06-15 14:41:57Z

You should not use lookarounds wrapped with anchors.

You can fix the issues with

RegExp regexUpper = RegExp(r'[A-Z]'); RegExp regexLower = RegExp(r'[a-z]'); RegExp regexLength = RegExp(r'^.{8,}$');

Look: ^(?=.*[A-Z])$ asserts the current position at the start of string (^), then checks if there is an uppercase ASCII letter ([A-Z]) anywhere after zero or more chars other than line break chars (as many as possible, with .*), and then requires the end of string ($) (right at the start of string). This is an example of a pattern that never matches any string.

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