检查以逗号分隔的小数点后的字符串-C＃

Question

I need to check this format;

1.234.567,89

Only one comma is permitted for the Entry.

Current code

Regex.Match(((TextChangedEventArgs)e).NewTextValue, @"^[0-9]+(\,[0-9]+)?$");

How can I achieve this?

Answer 1

You should not use regex to check if a string can be parsed to a decimal / double . Use decimal.TryParse (or double.TryParse ):

string moneyText = "1.234.567,89";
var myCulture = new CultureInfo("de-DE");
decimal money;
bool validFormat = decimal.TryParse(moneyText, NumberStyles.Currency, myCulture, out money);
if (validFormat)
    Console.WriteLine("Valid format, parsed value was " + money.ToString("C"));

Answer 2

Use regex to enforce possibilities by using non capturing lookaheads ( ?= ?! ) which we can enforce all rules before a match .

Rules are

• Only numbers, a comma or periods, a general rule.
• Only allow one comma
• Enforce a comma
• Don't allow two consecutive periods.

These patterns are commented so use the option IgnorePatternWhitespace or remove comments and join on one line.

Comma Required

^
(?=[\d\.,]+\Z) # Only allow decimals a period or a comma. 
(?=.*,)        # Enforce that there is a comma ahead.
(?!.*\.\.)     # Fail match if two periods are consecutive.
.+             # All rules satisfied, begin matching
$

Comma and following value optional

^
(?=[\d\.,]+\Z) # Only allow decimals a period or a comma. 
(?!.*\.\.)     # Fail match if two periods are consecutive.
[\d.]+         # All rules satisfied, begin matching
(,\d+)?        # If comma found, allow it but then only have decimals       
$              # This ensures there are no more commas and match will fail.