custom format or transform data in a MaskedTextBox during databinding

Question

I am looking for a way to display other data in a MaskedTextBox than the data it is bound to (DataTable).

More specifically: The DataTable contains a DateTime column (DateOfBirth). Whenever the year is 1900, I would like to display it as empty in the MaskedTextBox while keeping it in the underlying DataTable, because I use 1900 for "unknown".

Example: Value in the DataTable: 1900-10-09 --[DataBinding]--> MaskedTextBox __-10-09

Currently, I am using the CurrentItemChanged-Event of the BindingSource, to modify the Text-property of the MaskedTextBox. That works nicely as long as I simply browse through the DataTable. However, as soon as I start editing the MaskedTextBox, 1900 is back.

It would be nicer if I could somehow intercept the value that is passed from the DataRow to the MaskedTextBox, instead of replacing it afterwards.

Or maybe there is a way to get the MaskedTextBox to display 1900 as empty?

Answer 1

For completeness: Solution at codeproject

Have you tried Binding::Format and Binding::Parse? http://msdn.microsoft.com/en-US/library/system.windows.forms.binding_members(v=vs.80).aspx

Answer 2

I think that you need a ValueConverter. Create a class derived form IValueConverter and use it in your binding.

Answer 3

As Catalin pointed out, using the Binding.Format event did the trick:

Binding mtbGebdatBinding = mtbGebdat.DataBindings.Add("Text", _bsPerson, (string)mtbGebdat.Tag, true);
mtbGebdatBinding.Format += new ConvertEventHandler(mtbGebdatBinding_Format);
void mtbGebdatBinding_Format(object sender, ConvertEventArgs e)
{
    if (DBNull.Value != e.Value)
    {
       string date = String.Format("{0:dd/MM/yyyy}", (DateTime)e.Value);
        if (date.Substring(6, 4) == "1900")
        {
            e.Value = date.Substring(0, 6);
        }
    }
}