文本框十进制验证 - 省略点

Question

I'm doing a validation on TextBox where user must enter valid decimal text. Decimal represents amount of money.

Some examples of correct inputs:

1
1.000,99
1,99
1.000.000,99 etc.

Some examples of non-valid inputs:

1.0.0.0.0.
1.......0.0.0. etc.

Here is my validation code with TryParse method which I thought would solve everything:

   public void Validate_amount(string property_name, string string_value)
   {
        DeleteErrors(property_name);

        if (string.IsNullOrEmpty(string_value))//Ignore empty text
        {
            return;
        }
 
        bool is_amount = decimal.TryParse(string_value, out decimal n);
          
        if (!is_amount)
        {
            AddError(property_name, "Amount not correct");
            SystemSounds.Beep.Play();
        }
   }

Problem with this approach is that even examples of non-valid inputs are returned as True by TryParse method.

I can write as many of dots I like, and TryParse will allways return true. Comma however works as expected - only one is allowed.

How to fix this?

Answer 1

The TryParse method has a complete signature like this: TryParse (String, NumberStyles, IFormatProvider, Decimal) .

When you do not specify the 2nd and 3rd parameters, the default value is used for them.
For your example, the complete call will look like this:

bool is_amount = decimal.TryParse(
    string_value, 
    NumberStyles.Number, 
    NumberFormatInfo.CurrentInfo, 
    out decimal n);

The number of digits in groups is set in the NumberFormatInfo.CurrentInfo.CurrencyGroupSizes property (int []).
And it depends on the OS settings.
Let's say, on my computer, your incorrect examples all return false.

You can make a copy of the current value, change the properties you need and pass this instance to TryParse:

string string_value = "1.0.0.0.0.";

NumberFormatInfo numberFormatInfo = (NumberFormatInfo) NumberFormatInfo.CurrentInfo.Clone();

Debug.WriteLine(string.Join(", ", numberFormatInfo.CurrencyGroupSizes));

numberFormatInfo.CurrencyGroupSizes = new int[] { 3 };

Debug.WriteLine(decimal.TryParse(string_value, NumberStyles.Number, numberFormatInfo, out decimal number));