regex for alphanumeric only is not working

问题

This is the code I am trying:

string MatchNumberPattern = "^[a-zA-Z0-9]*$";

if (!Regex.IsMatch(cueTextBox9.Text, MatchNumberPattern))
{
    MessageBox.Show("Enter 8 Space Alphanumeric BT ID only");
    cueTextBox9.Text = String.Empty;
}
else
{
    do something();
}

It's accepting aaaaaaaa, but I want a combination of both alpha and numbers like aaaa1234.

回答1:

To require both a letter and a digit to appear in the input, you need positive lookaheads:

@"^(?=.*[a-zA-Z])(?=.*[0-9])[a-zA-Z0-9]*$"
    ^^^^^^^^^^^^^^^^^^^^^^^^

See the regex demo

The (?=.*[a-zA-Z]) makes sure there is a letter and (?=.*[0-9]) makes sure there is a digit in the input string.

Since you are taking the input from a single-line text box, it is safe to use . in the lookahead. As an alternative, you can use @"^(?=[^a-zA-Z]*[a-zA-Z])(?=[^0-9]*[0-9])[a-zA-Z0-9]*$" (based on the principle of contrast).

回答2:

You can use a lookahead to check for a digit and match an alpha before the rest.

^(?i)(?=\D*\d)\d*[A-Z][A-Z\d]*$

• ^ start of string
• (?i) flag for caseless matching
• (?=\D*\d) loook ahead for \D* any amount of non-digits followed by \d digit
• if succeeds match \d*[A-Z] any amount of digits followed by alpha
• [A-Z\d]* match any amount of alphanumeric characters until
• $ end of string

See demo at regex101

来源：https://stackoverflow.com/questions/35380322/regex-for-alphanumeric-only-is-not-working