Question

I have the following business object:

public class MyObject
{
  // Some public properties that are bound to text boxes, etc on the form
  public string Customer { get; set; }
  public int JobNumber { get; set; }

  // Each DataTable in this list consists of a single column of doubles
  // representing the error in a series of measurements (ex. -.0002, -.0003, .0002, etc)
  public List<DataTable> MeasurementErrors {get; set; }

  public MyObject
  {
    // Code in here creates the first DataTable with the first measurement (always zero)
    // and adds it to the MeasurementErrors list
    errors = new DataTable();
    errors.TableName = "MeasurementErrors";
    errors.Columns.Add("Error", typeof(double));
    errors.Rows.Add(0.0);
    MeasurementErrors.Add(errors); // initial table added to the list
  }
}

I’ve had no problems binding Customer and JobNumber and all the other basic properties to text boxes on the entry form (VS generated a BindingSource and set up all those controls for me).

What I’m having trouble with is binding one of the DataTables in MeasurementErrors to a DataGridView control. The table to bind should be chosen by a NumericUpDown control and then there will be a simple “Add” button to generate a new table and add it to MeasurementErrors (and a delete button if necessary). How do I set up the DataSource and DataMember properties of the DataGridView to bind to MeasurementErrors[value of UpDownControl]?

I’m not fixed on using DataTables but from what I’ve read that is the preferred way of binding to a DataGridView.

Answer 1

A List<T> is not bindable. Use an IList<T> instead as the property return type.

public IList<DataTable> MeasurementErrors { get; set; }

Plus, it is better recommended to use a internal list for list members and make it a read-only property, depending on your needs, always.

public class MyObject {
    private IList<DataTable> _measurementErrors;

    public MyObject() {
        _measurementErrors = new List<DataTable>();
    }

    // This way you make sure to never have a null reference, and don't give 
    // out the control over your list to the user.
    public IList<DataTable> MeasurementErrors {
        get {
            return _measurementErrors;
        }
    }
}

EDIT #1

IList doesn’t seem to be serializable so it is simply left out of the resulting xml file. Is there a simple way to make this IList serializable?

If your instance of IList<T> is a List<T> under the hood, then I suggest you to type-cast your IList<T> to a List<T> for the sake of serialization. And if that fails, then create a new list from its content.

var list = myObject1.MeasurementErrors as List<DataTable> ?? new List<DataTable>(myObject1.MeasurementErrors);

For more details about ?? Operator, please refer to MSDN: ?? Operator (C# Reference)

In short, it is the equivalence of writing:

var list = (myObject1.MeasurementErrors as List<DataTable>) == null ? 
            new List<DataTable>(myObject1.MeasurementErrors) : 
            myObject1.MeasurementErrors as List<DataTable>;

Or if you prefer:

var list = myObject1.MeasurementErrors as List<DataTable>;

if (list == null)
    list = new List<DataTable>(myObject1.MeasurementErrors);

I hope this information is not more confusing than helping.