.NET: combo box in data grid

I have adapted the C# code from
http://msdn.microsoft.com/msdnmag/issues/03/08/DataGrids/default.aspx for a
data grid combo box column and added it to my data grid. I don't get an
error but the column is simply not displayed (but if I query
VisibleColumnCount I get 7, which means it *should* be there, the row height
is also visibly larger). Can anybody spot what I might be missing/doing
wrong? TIA.

// init

ts := DataGridTableStyle.Create;

dc1 := DataGridTextBoxColumn.Create;

dc2 := DataGridBoolColumn.Create;

dc3 := DataGridTextBoxColumn.Create;

dc4 := DataGridTextBoxColumn.Create;

dc5 := DataGridTextBoxColumn.Create;

dc6 := DataGridTextBoxColumn.Create;

dc7 := DataGridComboBoxColumn.Create;

ts.MappingName := 'ODM';

ts.AlternatingBackColor := color.WhiteSmoke;

// column 1 - ordinary text box:

dc1.MappingName := 'fld_odmID';

dc1.HeaderText := 'ID';

dc1.Alignment := HorizontalAlignment.left;

dc1.NullText := '';

dc1.Width := 45;

<;snip - columns 2 - 6 are all text boxes>

// column 7 - the combo box:

SetLookupBinding(dc7.Combobx, 'fld_LastName', 'fld_ContactID',

ds.Tables['contact']); //see procedure below

dc7.HeaderText := 'Ansprechpartner';

dc7.Alignment := horizontalalignment.Left;

dc7.NullText := '';

dc7.Width := 150;

ts.PreferredRowHeight := dc7.Combobx.Height + 1;

ts.GridColumnStyles.Add(dc1);

ts.GridColumnStyles.Add(dc3);

ts.GridColumnStyles.Add(dc4);

ts.GridColumnStyles.Add(dc5);

ts.GridColumnStyles.Add(dc2);

ts.GridColumnStyles.Add(dc6);

ts.GridColumnStyles.add(dc7);

datagrid1.TableStyles.Add(ts);

procedure SetLookupBinding(combobx: System.Windows.Forms.Combobox;

DisplayColumn, BoundColumn: string; dt: DataTable);

begin

with combobx do

begin

DisplayMember := DisplayColumn;

ValueMember := BoundColumn;

DataSource := dt;

end;

end;

and the new class in a separate unit:

unit DataGridComboBoxColumnU;

interface

uses

System.Windows.Forms, System.Drawing, System.Data;

type

DataGridComboBoxColumn = class(System.Windows.Forms.DataGridTextBoxColumn)

private

{ Private-Deklarationen }

cm: CurrencyManager;

intCurrentRow: Integer;

cbb: Combobox; // Hosted combobox control

procedure comboBox_Leave(sender: System.Object; e: EventArgs );

procedure DataGrid_Scroll(sender: System.Object; e: EventArgs);

protected

procedure Edit(source: System.Windows.Forms.CurrencyManager;

rowNum: Integer; bounds: System.Drawing.Rectangle; readOnly: Boolean;

instantText: string; cellIsVisible: Boolean); override;

function GetColumnValueAtRow(source:
System.Windows.Forms.CurrencyManager;

rowNum: Integer): System.Object; override;

procedure SetColumnValueAtRow(source:
System.Windows.Forms.CurrencyManager;

rowNum: Integer; value: System.Object); override;

public

constructor Create;

function Combobx: Combobox;

end;

implementation

constructor DataGridComboBoxColumn.Create;

{Constructor - create combobox, register selection change event handler,

register lose focus event handler}

begin

inherited Create;

// Create combobox and force DropDownList style:

cbb := Combobox.Create;

cbb.DropDownStyle := ComboBoxStyle.DropDownList;

// Add event handler for notification when combobox loses focus:

Include(Self.cbb.Leave, Self.comboBox_Leave);

end;

function DataGridComboBoxColumn.Combobx: Combobox;

begin

Result := cbb;

end;

procedure DataGridComboBoxColumn.comboBox_Leave(sender: System.Object; e:
EventArgs );

{On combobox losing focus, set the column value, hide the combobox,

and unregister scroll event handler}

var

str: string;

rowView: DataRowView;

begin

rowView := DataRowView(cbb.SelectedItem);

str := string(rowView.Row[cbb.DisplayMember]);

SetColumnValueAtRow(cm, intCurrentRow, str);

Invalidate;

cbb.Hide;

Exclude(DataGridTableStyle.DataGrid.Scroll, DataGrid_Scroll);

end;

procedure DataGridComboBoxColumn.Edit(source:
System.Windows.Forms.CurrencyManager;

rowNum: Integer; bounds: System.Drawing.Rectangle; readOnly: Boolean;

instantText: string; cellIsVisible: Boolean);

// On edit, add scroll event handler, and display combobox

var rect: Rectangle;

begin

inherited Edit(source, rowNum, bounds, readOnly, instantText,

cellIsVisible);

if (not readOnly and cellIsVisible) then

begin

// Save current row in the DataGrid and currency manager

// associated with the data source for the DataGrid

intCurrentRow := rowNum;

cm := source;

// Add event handler for DataGrid scroll notification

include(DataGridTableStyle.DataGrid.Scroll, DataGrid_Scroll);

// Site the combobox control within the current cell

cbb.Parent := TextBox.Parent;

rect := DataGridTableStyle.DataGrid.GetCurrentCellBounds;

cbb.Location := rect.Location;

cbb.Size := Size.Create(TextBox.Size.Width, cbb.Size.Height);

// Set combobox selection to given text

cbb.SelectedIndex := cbb.FindStringExact(TextBox.Text);

// Make the combobox visible and place on top textbox control

cbb.Show;

cbb.BringToFront;

cbb.Focus;

end;

end;

function DataGridComboBoxColumn.GetColumnValueAtRow(

source: System.Windows.Forms.CurrencyManager; rowNum: Integer):
System.Object;

{Given a row, get the value member associated with a row. Use the

value member to find the associated display member by iterating

over bound data source}

var

obj: System.&amp;Object;

dv: DataView;

i: Integer;

begin

// Given a row number in the DataGrid, get the display member

obj := inherited GetColumnValueAtRow(source, rowNum);

// Iterate through the data source bound to the ColumnComboBox

cm :=
CurrencyManager(DataGridTableStyle.DataGrid.BindingContext[cbb.DataSource]);

// Assumes the associated DataGrid is bound to a DataView or

// DataTable

dv := DataView(cm.List);

for i := 0 to dv.Count - 1 do

if (obj.Equals(dv[i][cbb.ValueMember])) then

break;

// If set item was found return corresponding value,

// otherwise return DbNull.Value

if (i < dv.Count) then

Result := dv[i][cbb.DisplayMember];

Result := DBNull.Value;

end;

procedure DataGridComboBoxColumn.SetColumnValueAtRow(

source: System.Windows.Forms.CurrencyManager; rowNum: Integer;

value: System.Object);

{Given a row and a display member, iterate over bound data source to

find the associated value member. Set this value member.}

var

s: System.&amp;Object;

dv: DataView;

i: Integer;

begin

s := value;

// Iterate through the data source bound to the ColumnComboBox:

cm := CurrencyManager(

DataGridTableStyle.DataGrid.BindingContext[cbb.DataSource]);

// Assumes the associated DataGrid is bound to a DataView or

// DataTable

dv := DataView(cm.List);

for i := 0 to dv.Count - 1do

if (s.Equals(dv[i][cbb.DisplayMember])) then

break;

if i < dv.Count then

s := dv[i][cbb.ValueMember]

else

s := DBNull.Value;

inherited SetColumnValueAtRow(source, rowNum, s);

end;

procedure DataGridComboBoxColumn.DataGrid_Scroll(sender: System.Object; e:
EventArgs);

// On DataGrid scroll, hide the combobox

begin

cbb.Hide;

end;

end.

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