Converting to double is not allowing a zero after the decimal place

Question

I am working in WPF and C#, and have run into an issue which I think stems from my converter. I have a textbox where upon page load, an INT is converted to a DOUBLE and is displayed. Example:

Initial Value: 32.99
Can change to:
- 24
- 24.99
- 24.9
Unable to change to:
- 24.09

What happens is after I type 24.0, it instantly reverts to 24. I can achieve 24.09 by typing in 24.9 and then typing a 0 into the spot where I need it. I have tried to mess with my converter thinking that it was an issue with when/how I was converting it to a double but it is still producing the same results.

Here is the code for the converter:

    //This takes in an int and converts it to a double with two decimal places
    [ValueConversion(typeof(object), typeof(double))]
    public class conDouble : IValueConverter
    {
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            double db = System.Convert.ToDouble(value);
            return (db / 100.00).ToString();
        }
        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            return System.Convert.ToInt32((System.Convert.ToDouble(value) * 100));
        }
    }

The textbox in question with the regex:

<Page.Resources>
        <system:String x:Key="regexDouble">^\d+(\.\d{1,2})?$</system:String>            
</Page.Resources>
<TextBox Name="txtItemPrice" Grid.Column="12" Grid.ColumnSpan="2" Grid.Row="4" HorizontalAlignment="Stretch" VerticalAlignment="Center" IsEnabled="False" 
                 Validation.ErrorTemplate="{StaticResource validationTemplate}"
                 Style="{StaticResource textStyleTextBox}">
            <TextBox.Text>
                <Binding Path="intPrice" UpdateSourceTrigger="PropertyChanged" Mode="TwoWay" Converter="{StaticResource Double}">
                    <Binding.ValidationRules>
                        <classobjects:RegexValidation Expression="{StaticResource regexDouble}"/>
                    </Binding.ValidationRules>
                </Binding>
            </TextBox.Text>
        </TextBox>

And at last my validator:

public class RegexValidation : ValidationRule
    {
        private string pattern;
        private Regex regex;
        public string Expression
        {
            get { return pattern; }
            set
            {
                pattern = value;
                regex = new Regex(pattern, RegexOptions.IgnoreCase);
            }
        }
        public RegexValidation() { }
        public override ValidationResult Validate(object value, CultureInfo ultureInfo)
        {
            if (value == null || !regex.IsMatch(value.ToString()))
            {
                return new ValidationResult(false, "Illegal Characters");
            }
            else
            {
                return new ValidationResult(true, null);
            }
        }

    }

"This takes in an int and converts it to a double with two decimal places" There is no such thing as a double with two decimal places. If something has decimal places, it's a string; doubles are always binary, and are neutral with respect to their string representation. — John Wu, Jul 16 '18 at 21:05

score 0 · Accepted Answer · answered Jul 16 '18 at 21:42

In your converter, the line return (db / 100.00).ToString(); converts the double to a string, as John Wu mentioned. As a test, if you run the expression (24.0).ToString(), this results in "24". Since you are modeling a price, you could do something like (db / 100.00).ToString("F2"), which would result in "24.00", or (db / 100.00).ToString("C"), which would result in $24.00. You can find a full list of format strings at https://learn.microsoft.com/en-us/dotnet/standard/base-types/standard-numeric-format-strings. I am not fully following your implementation, but this would prevent the case where 24.0 automatically reverts to 24.

Also, be aware that decimal is a better data type for financial stuff than double is. See this link for more on that: decimal vs double! - Which one should I use and when?

Converting to double is not allowing a zero after the decimal place

1 Answers1