Multiple specific selection in SAP B1 ChooseFromList

I recently had the need to create a selection type that would allow selection of specific values (multiple ones) from a ChooseFromList. The basic case of single selection and range selection also had to be supported.
As an example, consider the ChooseFromList from Items. I needed to be able to select A1, A3, A5 – A10.
The selection would look like A1, A3, A5, A6, A7, A8, A9, A10. In other words A2, A4 would be ignored as they were not on the selection.
To achieve this, multiple selection on the ChooseFromList object was activated to be able to select multiple values. But, the EditText which “contains” the ChooseFromList can only contain one object and it was linked with a UserDataSource (which allows only one value to be saved). In order to save multiple selected values a DataTable was added to the form’s data source collection.

<DataTables>
  <DataTable Uid="DT_0">
    <Columns/>
  </DataTable>
</DataTables>

Once the DataTable was added the ChooseFromList event could now be used to save the selected values into this DataTable.

if (cflEvent.SelectedObjects != null && cflEvent.SelectedObjects.Rows.Count == 1)
{
	oItem.TextStyle = (int)BoTextStyle.ts_PLAIN_FONT;
	string SelectedValue = cflEvent.SelectedObjects.GetValue(e.ChooseFromListAlias, 0) as string;
	d.ValueEx = SelectedValue;
}
else if(cflEvent.SelectedObjects != null && cflEvent.SelectedObjects.Rows.Count > 1)
{
	oItem.TextStyle = (int)BoTextStyle.ts_BOLD;
	string SelectedValue = cflEvent.SelectedObjects.GetValue(e.ChooseFromListAlias, 0) as string;
	d.ValueEx = SelectedValue;

	selection.CopyFrom(cflEvent.SelectedObjects);
}

Some care had to be taken in order to clear the DataTable every time the selection on this particular ChooseFromList was changed.
For this, a simple XPath expression is evaluated to check the current ChooseFromList allows for multiple selections. If so, then it clears the DataTable before saving the new selection.

DataTable selection = oForm.DataSources.DataTables.Item("DT_0");
XPathDocument doc = new XPathDocument(new StringReader(oForm.GetAsXML()));
XPathNavigator nav = doc.CreateNavigator();
string xpath = string.Format("//ChooseFromList[@UniqueID='{0}']/@MultiSelection", e.ChooseFromListUID);
XPathNodeIterator iter = nav.Select(xpath);

iter.MoveNext();
if (iter.Current.Value == "1")
	selection.Clear();

After adding the values to the DataTable the user is given a hint that multiple values are selected by making the text on the EditText bold. Also if a user double clicks the text on the EditText a small Grid displays the selected objects.

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