This behavior can be seen when you embedded a control like a textbox or combobox in your derived GridColumnStyle. If you press the tabkey slowly, you may see the cell get focus on the downkey and the cell lose focus on the upkey. One way to avoid this problem is to subclass the embedded control, and override its WndProc method, ignoring the KeyUp.

[C#]
public class MyCombo : ComboBox
{
         private const int WM_KEYUP = 0x101;

         protected override void WndProc(ref System.Windows.Forms.Message m)
         {
                  if(m.Msg == WM_KEYUP)
                  {
                           return;  //ignore the keyup
                  }
                  base.WndProc(ref m);
         }
}

[VB.NET]
Public Class MyTextBox
	Inherits TextBox
	Private WM_KEYUP As Integer = &H101
 
	Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)
		If m.Msg = WM_KEYUP Then
			Return ’ignore the keyup
		End If
		MyBase.WndProc(m)
	End Sub ’WndProc
End Class ’MyTextBox

Set the

 DataGrid.AllowNavigation

property to false.

If you have added a table style to your datagrid (so individual column styles have been generated), then you can use code such as this to set the Format property of the particular column style.

[C#]
	//add format col 3 columnstyle where column 3 holds a date...

	DataGridTextBoxColumn dgtbc;
	dgtbc = dataGrid1.TableStyles[0].GridColumnStyles[3] as DataGridTextBoxColumn;

	if(dgtbc != null)
	 	dgtbc.Format = 'g'; // or 'u' or whatever format you want to see

[VB.NET]
	’add format col 3 columnstyle where column 3 holds a date...

	Dim dgtbc as DataGridTextBoxColumn 
	dgtbc = CType(dataGrid1.TableStyles(0).GridColumnStyles(3),  DataGridTextBoxColumn)

	If Not dgtbc is Nothing Then
	 	dgtbc.Format = 'g'  ’ or 'u' or whatever format you want to see
	End If

The method DataGrid.IsSelected can tell you if a particular row is selected.
So, you could use IsSelected in a loop through all your rows to finds if
multiple rows have been selected. Depending upon the size of your datagrid,
this may be a viable solution. If not, you could track the selections
yourself by monitoring the key actions and the mouse actions. This would be
more work. Thanks to John Hughes to the suggestion to use the dataview.

[C#]
public ArrayList GetSelectedRows(DataGrid dg)
{
	ArrayList al = new ArrayList();
	CurrencyManager cm = (CurrencyManager)this.BindingContext[dg.DataSource, dg.DataMember];    
    	DataView dv = (DataView)cm.List;
    
	for(int i = 0; i < dv.Count; ++i)
	{
		if(dg.IsSelected(i))
			al.Add(i);
	}
	return al;
}

private void button1_Click(object sender, System.EventArgs e)
{
	string s = 'Selected rows:';
	foreach(object o in GetSelectedRows(dataGrid1))
	{
		s+=''+o.ToString();
	}
	MessageBox.Show(s);
}

[VB.NET]
	Public Function GetSelectedRows(ByVal dg As DataGrid) As System.Collections.ArrayList
		Dim al As New ArrayList()

		Dim cm As CurrencyManager = Me.BindingContext(dg.DataSource, dg.DataMember)
		Dim dv As DataView = CType(cm.List, DataView)
   
		Dim i As Integer
		For i = 0 to dv.Count - 1
			If dg.IsSelected(i) Then
				al.Add(i)
			End If
		End Next
		Return al
	End Function ’GetSelectedRows
	
	 Private Sub button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
		 Dim s As String = 'Selected rows:'
		Dim o As Object
		For Each o In GetSelectedRows(dataGrid1)
			s += ' ' + o.ToString()
		Next o
		MessageBox.Show(s)
	 End Sub ’button1_Click

If you make sure your DataGrid is using a DataGridTableStyle, then you can access the TextBox through the GridColumnStyles collection and hook the event there. Here is some code….

[C#]
	//in formload
	this.dataGrid2.DataSource = this.dataSet11.Customers; // set the data source

            	//make sure grid has a tablestyle
	DataGridTableStyle ts = new DataGridTableStyle();
	ts.MappingName = this.dataSet11.Customers.TableName;
	this.dataGrid2.TableStyles.Add(ts);

	//now we can wire up wire up events for columns 1 and 4 ....
	DataGridTextBoxColumn tbc = (DataGridTextBoxColumn)ts.GridColumnStyles[0];
	tbc.TextBox.KeyPress += new KeyPressEventHandler(CellKeyPress);

	tbc = (DataGridTextBoxColumn)ts.GridColumnStyles[3];
	tbc.TextBox.KeyPress += new KeyPressEventHandler(CellKeyPress);.....

	//the handler
	private void CellKeyPress(object sender, KeyPressEventArgs e)
	{
		//don’t allow 1’s
		if(e.KeyChar == ’1’)
		e.Handled = true;
	}

[VB.NET]
	 ’in formload
	Me.dataGrid2.DataSource = Me.dataSet11.Customers ’ set the data source
	
	’make sure grid has a tablestyle
	Dim ts As New DataGridTableStyle()
	ts.MappingName = Me.dataSet11.Customers.TableName
	Me.dataGrid2.TableStyles.Add(ts)

	’now we can wire up wire up events for columns 1 and 4 ....
	Dim tbc as DataGridTextBoxColumn = CType(ts.GridColumnStyles(0), DataGridTextBoxColumn)
	AddHandler tbc.TextBox.KeyPress, AddressOf CellKeyPress

	tbc = CType(ts.GridColumnStyles(3), DataGridTextBoxColumn)
	AddHandler tbc.TextBox.KeyPress, AddressOf CellKeyPress
	.....

	’the handler
	Private Sub CellKeyPress(sender As Object, e As KeyPressEventArgs) 
   		’don’t allow 1’s
		If e.KeyChar = '1'c Then
			e.Handled = True
		End If
	End Sub ’CellKeyPress

When you first click into a checkbox column, the checked state of the cell does not change. One way you can make the checked state change on the first click is to handle the grid’s MouseUp event, and change the check value there.

[VB.Net}
	Private myCheckBoxCol As Integer = 9  ’my checkbox column
	Private Sub DataGrid2_MouseUp(ByVal sender As Object,  ByVal e As MouseEventArgs) Handles DataGrid2.MouseUp
		Dim hti As DataGrid.HitTestInfo = Me.dataGrid2.HitTest(e.X, e.Y)
		Try
			If hti.Type = DataGrid.HitTestType.Cell AndAlso hti.Column = myCheckBoxCol Then
				Me.dataGrid2(hti.Row, hti.Column) = Not CBool(Me.dataGrid2(hti.Row, hti.Column))
			End If
		Catch ex As Exception
			MessageBox.Show(ex.ToString())
		End Try
	End Sub ’dataGrid2_MouseUp

[C#]
	private int myCheckBoxCol = 9; //my checkbox column

	private void dataGrid2_MouseUp(object sender, System.Windows.Forms.MouseEventArgs e)
	{
		DataGrid.HitTestInfo hti   = this.dataGrid2.HitTest(e.X, e.Y);
		try
		{
			if( hti.Type == DataGrid.HitTestType.Cell && 
				hti.Column == myCheckBoxCol)
			{
				this.dataGrid2[hti.Row, hti.Column] = ! (bool) this.dataGrid2[hti.Row, hti.Column];
			}
		}																				catch(Exception ex)
		{
			MessageBox.Show(ex.ToString());
		}
	}

Derive a DataGrid. In your derived grid, add a handler for the VertScrollBar.VisibleChanged event. In your handler, if the scrollbar is not visible, size it and position it, and then show it. The code below assumes no horizontal scrollbar is necessary. If it is present, you would have to adjust the sizing code.

C#
public class MyDataGrid : DataGrid
{

	public MyDataGrid()
	{
		//make scrollbar visible & hook up handler
		this.VertScrollBar.Visible = true;
		this.VertScrollBar.VisibleChanged += new EventHandler(ShowScrollBars);
	}

	private int CAPTIONHEIGHT = 21;
	private int BORDERWIDTH = 2;
	
	private void ShowScrollBars(object sender, EventArgs e)
	{
		if(!this.VertScrollBar.Visible)
		{
			int width = this.VertScrollBar.Width;
			this.VertScrollBar.Location = new Point(this.ClientRectangle.Width - width  - BORDERWIDTH, CAPTIONHEIGHT);
			this.VertScrollBar.Size = new Size(width, this.ClientRectangle.Height - CAPTIONHEIGHT - BORDERWIDTH);
			this.VertScrollBar.Show();				
		}
	}
}

VB.NET
Public Class MyDataGrid
	Inherits DataGrid
   
	Public Sub New()
		’make scrollbar visible & hook up handler
		Me.VertScrollBar.Visible = True
		AddHandler Me.VertScrollBar.VisibleChanged, AddressOf ShowScrollBars
	End Sub ’New
   
	Private CAPTIONHEIGHT As Integer = 21
	Private BORDERWIDTH As Integer = 2
   
	Private Sub ShowScrollBars(sender As Object, e As EventArgs)
		If Not Me.VertScrollBar.Visible Then
			Dim width As Integer = Me.VertScrollBar.Width
			Me.VertScrollBar.Location = New Point(Me.ClientRectangle.Width - width - BORDERWIDTH, CAPTIONHEIGHT)
			Me.VertScrollBar.Size = New Size(width, Me.ClientRectangle.Height - CAPTIONHEIGHT - BORDERWIDTH)
			Me.VertScrollBar.Show()
		End If
	End Sub ’ShowScrollBars
End Class ’MyDataGrid

The DataGrid class does not have a property that controls whether a new row can be added. But the DataView class does have such a property (along with some others such as AllowEdit and AllowDelete). Here is code that will turn off the append row by getting at the dataview associated with the datagrid.

	string connString = @'Provider=Microsoft.JET.OLEDB.4.0;data source=C:\northwind.mdb';
	string sqlString = 'SELECT * FROM customers';

	// Connection object
	OleDbConnection connection = new OleDbConnection(connString);

	// Create data adapter object
	OleDbDataAdapter dataAdapter = new OleDbDataAdapter(sqlString, connection);

	// Create a dataset object and fill with data using data adapter’s Fill method
	DataSet dataSet = new DataSet();
	dataAdapter.Fill(dataSet, 'customers');
			
	// Attach dataset’s DefaultView to the datagrid control
	dataGrid1.DataSource = dataSet.Tables['customers'];

	//no adding of new rows thru dataview...
	CurrencyManager cm = (CurrencyManager)this.BindingContext[dataGrid1.DataSource, dataGrid1.DataMember];	
	((DataView)cm.List).AllowNew = false;

If your datagrid contains links, then Matthew Miller suggest adding Navigate handler such as the one below to disallow the AddNew.

private void DataGrid1_Navigate(object sender, System.Windows.Forms.NavigateEventArgs ne)
{
	if(ne.Forward)
	{
		CurrencyManager cm  = (CurrencyManager)BindingContext[DataGrid1.DataSource,DataGrid1.DataMember];
		DataView dv  = (DataView) cm.List;
		dv.AllowNew = false;
	}
}