Question

I’ve got DataGridView bound to a DataTable with some numeric data and I need two things to ensure are working:

1. Numeric sorting (doubles/ints) on every column with numbers,
2. Possibility to add some text (like ‘x’ or ‘-‘) instead of numbers in special cases.

Is there a simple way I could add them at the level of DataTable?

I know I can change type of DataTable‘s columns to String, but then I’d need to add much more code just for the sake of sorting columns by already built-in way – and I certainly don’t need to change the way glyphs are drawn, etc.

Also, because of amount and way my DGVs are spawned, it won’t be as easy as adding one method for every DGV I’ve got.

[Edit]

I write the same set of DataTables to excel files, so drastic changes to the way they work would be problematic and error prone – I’d like to avoid it.

My code for filling dataTables in most occasions looks like this:

var row = MyDataTable.GetMyDataTableNewRow();  
row.partName = part.name;  
row.weight = part.weight.ToString();  // it's double  
row.quantity = part.GetParentSet().FindQuantities(part.name).ToString(); // it's int  
row.maxsize = part.CalculateMaxSize().ToString();  
MyDataTable.AddMyDataTableRow(row);

Answer 1

The only way to define you desired behaviour at DataTable level, is introducing a custom type holding both a double and a string, and defining an appropriate TypeConverter (to correctly show the objects and enable editing in the DataGridView).

e.g. :

[TypeConverter(typeof(DoubleOrTextConverter))]
public class DoubleOrText : IComparable
{
    public double Value { get; private set; }
    public string Text { get; private set; }
    public DoubleOrText(double val, string text)
    {
        this.Value = val;
        this.Text = text;
    }
    public static DoubleOrText FromString(System.Globalization.CultureInfo culture, string str)
    {
        double v;
        if (double.TryParse(str, out v))
            return new DoubleOrText(v, null);
        return new DoubleOrText(0, str);
    }
    public string ToString(System.Globalization.CultureInfo culture)
    {
        if (this.Text != null)
            return this.Text;
        return this.Value.ToString(culture);
    }
    // define your sorting strategy here
    public int CompareTo(object obj)
    {
        if (obj == null) return 1;

        var other = obj as DoubleOrText;
        if (other != null)
            return this.Value.CompareTo(other.Value);
        else
            throw new ArgumentException("Object is not a DoubleOrText");
    }
}

public class DoubleOrTextConverter : TypeConverter
{
    public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
    {
        if (sourceType == typeof(string))
            return true;
        return base.CanConvertFrom(context, sourceType);
    }
    public override object ConvertFrom(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value)
    {
        if (value is string)
            return DoubleOrText.FromString(culture, value as string);
        return base.ConvertFrom(context, culture, value);
    }
    public override object ConvertTo(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value, Type destinationType)
    {
        if (destinationType == typeof(string))
        {
            var dValue = (DoubleOrText)value;
            return dValue.ToString(culture);
        }
        return base.ConvertTo(context, culture, value, destinationType);
    }
}

Usage example:

DataTable dt = new DataTable();
dt.Columns.Add("Column 1", typeof(DoubleOrText));

dt.Rows.Add(new DoubleOrText(0.0, null));
dt.Rows.Add(new DoubleOrText(1.0, "X"));
dt.Rows.Add(new DoubleOrText(2.3, "-"));
dt.Rows.Add(new DoubleOrText(4.1, null));

this.dataGridView1.DataSource = dt;

Result: