I am using Ultragrid in c# .net windows application,
I used a column of datatype System.DateTime., On page loading it is showing empty (like '--/--/--'),
aftrer some validations i want to make that column empty
when am trying to make that column empty, it is taking current date as default or '01/01/0001'.
i made defaultvalue to null.
How to make empty that column means it should show like '--/--/--'
This is probably an issue with your DataSource, not the grid.
The DateTime data type in DotNet is a struct, so it can't be null. If you use a DataSet/DataTable or UltraDataSource as the data source for your grid, then these objects store everything as an object so that they can handle null or DBNull. My guess is that you are probably binding the grid to a list of your own custom classes and the DataType of the field is DateTime and cannot accept nulls.
If you are using CLR2, maybe you can use a nullable DateTime, instead. You might have to set the Nullable property on the column to Nothing, though, since even a nullable type can't handle DBNull.