flutter textfield validation listener code example

Example 1: text input validation message color flutter

TextFormField(
  decoration: InputDecoration(
     errorStyle: TextStyle(
      color: Colors.red[400],
      fontWeight: FontWeight.bold,
      fontSize: 13,
    ),
  ),
  ...
)

Example 2: flutter text form field email validation

String validateEmail(String value) {
    Pattern pattern =
        r"^[a-zA-Z0-9.!#$%&'*+/=?^_`{|}~-]+@[a-zA-Z0-9](?:[a-zA-Z0-9-]"
        r"{0,253}[a-zA-Z0-9])?(?:\.[a-zA-Z0-9](?:[a-zA-Z0-9-]"
        r"{0,253}[a-zA-Z0-9])?)*$";
    RegExp regex = new RegExp(pattern);
    if (!regex.hasMatch(value) || value == null)
      return 'Enter a valid email address';
    else
      return null;
  }