Question

I have several TextBoxes, which display angular values. I format these using different custom implementations of IFormatProvider, for example: The value 1.5707963267949 can be displayed as 1.5707963267949, 0.5π or 90°. The TextBoxes are one-way-databound and I perform the formatting by handling the Format event of the Binding:

void bindingToMyTextBox_Format(object sender, ConvertEventArgs e)
{
    // angleValueFormat is one of a few a custom implementations of 
    // IFormatProvider performing the actual formatting work.
    e.Value = String.Format(this.angleValueFormat, "{0:0.###}", (double)e.Value);
}

I want to allow the user to input values in the same format as they are displayed in. So I need to parse TextBox.Text to obtain the original value 1.5707963267949. Is there any "IParserProvider" interface providing parsing services, like IFormatProvider in the opposite direction? Or would you suggest a different approach?

From what I understand, i can’t use my IFormatProviders in the Convert.ToDouble Method (String, IFormatProvider) because, to determine in which format the number to parse is, it uses only the NumberFormatInfo-Object returned by the IFormatProvider.GetFormat(), which I obviously can’t use to specify the necessary info.

Thank you!

richn

Answer 1

No, that’s not possible. I think mostly because in general it’s not possible to automatically deduce a parser from a formatter (which is, iirc, internally implemented by a method ICustomFormatter.Format).

I would suggest to define your own interface

public interface IAngleParser {
    double ParseAngle(string);
}

and implement it in your classes for the angleValueFormat mamber. You’ll probably have to use some regexes or so to do that.

Then you can use

void bindingToMyTextBox_Parse(object sender, ConvertEventArgs e) {
    e.Value = ((IAngleParser)this.angleValueFormat).ParseAngle(e.Value);
}

and bind this to your binding’s Parse event.