I have been working on a custom datagridcolumnstyle that uses a combo box when in edit mode. It the box is showing, but not expanded and I click on another cell in the same row, I get a null reference exception without source code. If I click on another row I get an object not set to reference error, but it shows a dialog box. If I expand the combo box it works just fine. I am thinking it is an internal bug, but how do I work around it?
I would show code, but it is way to large. Here is the style code though.
I would show code, but it is way to large. Here is the style code though.
Public Class HSDropBoxColumn
Inherits DataGridColumnStyle
Implements IColumnInterface
Implements ISetCellFormat
Friend WithEvents mListBox As New ComboBox
Private mDataGrid As DataGrid = Nothing
Private mblnIsEditing As Boolean = False
Public Sub New(ByVal Values As String())
mListBox.Items.AddRange(Values)
mListBox.Visible = False
mListBox.Height = 50
mListBox.DropDownStyle = ComboBoxStyle.DropDownList
End Sub
Protected Overrides Sub Abort(rowNum As Integer)
mblnIsEditing = False
mDataGrid.Controls.Remove(mListBox)
Invalidate()
End Sub
Protected Overrides Function Commit(dataSource As System.Windows.Forms.CurrencyManager, rowNum As Integer) As Boolean
If Not mblnIsEditing Then
Return True
End If
If mListBox Is Nothing Then Return True
mblnIsEditing = False
Dim objOld, objNew As Object
Try
objOld = GetColumnValueAtRow(dataSource, rowNum)
Catch exr As IndexOutOfRangeException
Return True
Exit Function
End Try
Try
objNew = mListBox.SelectedItem.ToString
Catch ex As Exception
Return True
End Try
If objOld Is DBNull.Value And objNew Is DBNull.Value Then
Return False
ElseIf objOld Is DBNull.Value And Not objNew Is DBNull.Value Then
If TypeOf objNew Is String Then
SetColumnValueAtRow(dataSource, rowNum, CStr(objNew))
OnCellValueChanged(New CellValueChangedEventArgs(rowNum, Me.DataGridTableStyle.GridColumnStyles.IndexOf(Me), objOld, objNew))
Else
Return False
End If
ElseIf Not objOld Is DBNull.Value And objNew Is DBNull.Value Then
SetColumnValueAtRow(dataSource, rowNum, DBNull.Value)
OnCellValueChanged(New CellValueChangedEventArgs(rowNum, Me.DataGridTableStyle.GridColumnStyles.IndexOf(Me), objOld, objNew))
ElseIf Not objOld Is DBNull.Value And Not objNew Is DBNull.Value Then
If TypeOf objOld Is String And TypeOf objNew Is String Then
If CStr(objOld) <> CStr(objNew) Then
SetColumnValueAtRow(dataSource, rowNum, CStr(objNew))
OnCellValueChanged(New CellValueChangedEventArgs(rowNum, Me.DataGridTableStyle.GridColumnStyles.IndexOf(Me), objOld, objNew))
Else
Return False
End If
End If
End If
Invalidate()
Me.mListBox.Visible = False
Return True
End Function
Protected Overrides Function GetMinimumHeight() As Integer
Return mListBox.PreferredHeight + 4
End Function
Protected Overrides Function GetPreferredHeight(g As System.Drawing.Graphics, value As Object) As Integer
Return mListBox.PreferredHeight + 4
End Function
Protected Overrides Function GetPreferredSize(g As System.Drawing.Graphics, value As Object) As System.Drawing.Size
Return New Size(100, mListBox.PreferredHeight + 4)
End Function
Protected Overloads Overrides Sub Paint(ByVal g As System.Drawing.Graphics, ByVal bounds As System.Drawing.Rectangle, ByVal source As System.Windows.Forms.CurrencyManager, ByVal rowNum As Integer)
Paint(g, bounds, [source], rowNum, False)
End Sub
Protected Overloads Overrides Sub Paint(ByVal g As System.Drawing.Graphics, ByVal bounds As System.Drawing.Rectangle, ByVal source As System.Windows.Forms.CurrencyManager, ByVal rowNum As Integer, ByVal alignToRight As Boolean)
Paint(g, bounds, [source], rowNum, Brushes.Red, _
Brushes.Blue, alignToRight)
End Sub
Protected Overloads Overrides Sub Paint(ByVal g As Graphics, _
ByVal bounds As Rectangle, ByVal [source] As CurrencyManager, _
ByVal rowNum As Integer, ByVal backBrush As Brush, _
ByVal foreBrush As Brush, ByVal alignToRight As Boolean)
Dim e As HSDataGridFormatCellEventArgs = Nothing
Dim pintCol As Integer = 0
Try
e = New HSDataGridFormatCellEventArgs(rowNum, pintCol, Me.GetColumnValueAtRow([source], rowNum))
RaiseEvent SetCellFormat(Me, e)
Catch ex As Exception
End Try
Dim pstrVal As String = String.Empty
Try
pintCol = Me.DataGridTableStyle.GridColumnStyles.IndexOf(Me)
Catch ex As Exception
End Try
If TypeOf source.Current Is DataRowView Then
Dim drv As DataRowView = DirectCast(source.Current, DataRowView)
Dim r As DataRow = drv.DataView.Table.Rows(rowNum)
End If
g.FillRectangle(backBrush, bounds)
'RaiseEvent SetCellFormat(Me, e)
' assume we will call the baseclass
Dim callBaseClass As Boolean = True
Dim pbrshBackBrush As SolidBrush
Dim pbrshForeBrush As SolidBrush
' check the brushes returned from the event
If Not (e.BackBrush Is Nothing) Then
pbrshBackBrush = e.BackBrush
Else
pbrshBackBrush = New SolidBrush(Color.White)
End If
If Not (e.ForeBrush Is Nothing) Then
pbrshForeBrush = e.ForeBrush
Else
pbrshForeBrush = New SolidBrush(Color.Black)
End If
Me.DataGridTableStyle.HeaderBackColor = e.HeaderBackColor
Me.DataGridTableStyle.HeaderForeColor = e.HeaderForeColor
Me.DataGridTableStyle.GridLineColor = e.GridLineColor
' check the UseBaseClassDrawing property
If Not e.UseBaseClassDrawing Then
callBaseClass = False
End If
If e.CurrentCellValue Is DBNull.Value Then
pstrVal = "[null]"
Else
pstrVal = CStr(e.CurrentCellValue)
End If
Try
g.FillRectangle(pbrshBackBrush, bounds)
Dim pt As New PointF
Dim f As Font = Me.DataGridTableStyle.DataGrid.Font
Dim siz As SizeF = g.MeasureString(pstrVal, f)
Dim psngTop As Single = (bounds.Height \ 2) - (siz.Height \ 2)
psngTop = bounds.Top + psngTop
Dim r As New RectangleF(bounds.X, psngTop, bounds.Width, siz.Height)
Dim sf As New StringFormat
If alignToRight Then
sf.LineAlignment = StringAlignment.Far
Else
sf.LineAlignment = StringAlignment.Near
End If
g.DrawString(pstrVal, f, pbrshForeBrush, r, sf)
sf.Dispose()
Catch ex As Exception
End Try
End Sub
Protected Overrides Sub SetDataGridInColumn(ByVal value As DataGrid)
MyBase.SetDataGridInColumn(value)
If Not value Is Nothing Then
mDataGrid = value
End If
End Sub
Protected Overridable Sub OnCellValueChanged(ByVal e As CellValueChangedEventArgs)
RaiseEvent CellValueChanged(Me, e)
End Sub
Protected Overloads Overrides Sub Edit(ByVal source As System.Windows.Forms.CurrencyManager, ByVal rowNum As Integer, ByVal bounds As System.Drawing.Rectangle, ByVal [readOnly] As Boolean, ByVal instantText As String, ByVal cellIsVisible As Boolean)
Dim objVal As Object = GetColumnValueAtRow([source], rowNum)
Dim value As String = String.Empty
If Not TypeOf objVal Is DBNull Then
value = CStr(objVal)
End If
If mListBox Is Nothing Then Exit Sub
mDataGrid.Controls.Add(mListBox)
If cellIsVisible Then
mListBox.Width = bounds.Width
mListBox.Location = bounds.Location
mListBox.Height = 50
mListBox.SelectedItem = value
mListBox.Visible = True
Else
mListBox.SelectedItem = value
mListBox.Visible = False
End If
If mListBox.Visible Then
DataGridTableStyle.DataGrid.Invalidate(bounds)
End If
Me.mblnIsEditing = True
mListBox.Focus()
End Sub
Public Event CellValueChanged(sender As Object, e As CellValueChangedEventArgs) Implements IColumnInterface.CellValueChanged
Public Event SetCellFormat(sender As Object, e As HSDataGridFormatCellEventArgs) Implements ISetCellFormat.SetCellFormat
End Class
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