问题
I have a DGV in VB.Net 2008 connected to an Access DB table. The DGV is not Read Only, but is full of read-only columns except for one, which contains a combo box. The combo box allows the user to select an outcome for that particular row, and then the program copies in a pre calculated value into the "Profit" column depending upon the item selected in the combobox. Then the user hits the Save button and the DB updates (currently via SQL methods in the XSD).
Easy enough so far.
Here is the code.
Private Sub DGUserBets_EditingControlShowing(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewEditingControlShowingEventArgs) Handles DGUserBets.EditingControlShowing
Dim combo As ComboBox = CType(e.Control, ComboBox)
If (combo IsNot Nothing) Then
// Remove an existing event-handler, if present, to avoid
// adding multiple handlers when the editing control is reused.
RemoveHandler combo.SelectedIndexChanged, _
New EventHandler(AddressOf DGUBStake_SelectedIndexChanged)
// Add the event handler.
AddHandler combo.SelectedIndexChanged, _
New EventHandler(AddressOf DGUBStake_SelectedIndexChanged)
End If
End Sub
Private Sub DGUBStake_SelectedIndexChanged(ByVal sender As Object, ByVal e As EventArgs)
Dim myStatus As ComboBox = CType(sender, ComboBox)
Dim row = DGUserBets.CurrentRow
Select Case myStatus.SelectedIndex
Case 0
row.Cells("DGUBProfit").Value = 0
// pending. no action
Case 1
row.Cells("DGUBProfit").Value = row.Cells("DGUBIfWin").Value
// win
Case 2
// loses
row.Cells("DGUBProfit").Value = row.Cells("DGUBIfLose").Value
Case 3
// void
row.Cells("DGUBProfit").Value = 0
End Select
End Sub
The problem I have is that it would seem that if a user selects the desired outcome from the combobox but does NOT hit Enter, and simply mouses on to a different combobox to again select the outcome for a different row, the first eventhandler is not disconnected and thus the events fire multiple times. This then causes various default MsgBox errors and brings up problems when the user tries to commit all changes to the DB/exit program etc etc.
What do I need to do? Do I need to .EndEdit somewhere appropriate to force the row to save the changes? And where should I call this?
Thank you.
回答1:
A quick glance at the code brings up this question: If you create a new EventHandler when removing the existing one is it the same one?
回答2:
I have had a similar issue, add a handler for CellLeave if the cell being exited is the cell you are looking for (IE e.ColumnIndex = myEditableColumn.Index) then call gv.EndEdit()
Also I would recommend making the handlers member variables for assignment and removal because it seems nicer then always saying Remove New and Add New.
回答3:
CKRet/Quintin , thank you for the fast responses.
A quick try with this code seems better and breakpointing and stepping through the code seems to be firing the events correctly. I'm fairly new to .NET as the last real VB programming I did was VB6 so I'm not sure if this is the most elegant way to solve the problem.
Also a note that when LastEventHandler = Nothing, calling the RemoveHandler does not throw an exception, which is quite nice.
Maybe I should suggest to MS they should update that article.
Private Sub DGUserBets_EditingControlShowing(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewEditingControlShowingEventArgs) Handles DGUserBets.EditingControlShowing
Dim combo As ComboBox = CType(e.Control, ComboBox)
Static LastEventHandler As EventHandler
If (combo IsNot Nothing) Then
// Remove an existing event-handler, if present, to avoid
// adding multiple handlers when the editing control is reused.
RemoveHandler combo.SelectedIndexChanged, _
LastEventHandler
LastEventHandler = New EventHandler(AddressOf DGUBStake_SelectedIndexChanged)
// Add the event handler.
AddHandler combo.SelectedIndexChanged, _
LastEventHandler
End If
End Sub
回答4:
Simpler code which also appears to work well, as suggested by CKRet:
Dim combo As ComboBox = CType(e.Control, ComboBox)
If (combo IsNot Nothing) Then
RemoveHandler combo.SelectedIndexChanged, AddressOf DGUBStake_SelectedIndexChanged
AddHandler combo.SelectedIndexChanged, AddressOf DGUBStake_SelectedIndexChanged
End If
回答5:
I know this is an archaic post, but after buggering around with this same problem for half a day I've found a way to solve this another way, so I thought it would be worth sharing.
Adding a second handler to handle the leave event of the combobox which then removes the handler of selectedvalue changed. Appears to work quite slick, and unlike another option i found gives the desired resulting action (unlike removing the value changed handler on the actual handling event which then won't fire if you re-select from the same combobox)
Private LastEventHandler As EventHandler = AddressOf Me.ComboBoxValueChanged
Private Sub dgvThisDatagrid_EditingControlShowing(sender As Object, e As System.Windows.Forms.DataGridViewEditingControlShowingEventArgs) Handles dgvOutstandingReminders.EditingControlShowing
If TypeOf (e.Control) Is ComboBox Then
Dim cboThisComboBox = DirectCast(e.Control, ComboBox)
AddHandler cboThisComboBox.SelectedValueChanged, LastEventHandler
AddHandler cboThisComboBox.Leave, AddressOf RemoveValueChangedHandler
End If
End Sub
Private Sub ComboBoxValueChanged(ByVal sender As Object, ByVal e As System.EventArgs)
If TypeOf (sender) Is ComboBox Then
Dim cboThisComboBox = DirectCast(sender, ComboBox)
MessageBox.Show("Value = " & cboThisComboBox.SelectedValue.ToString() & Environment.NewLine & "Text = " & cboThisComboBox.Text) ' Display index
End If
End Sub
Private Sub RemoveValueChangedHandler(ByVal sender As Object, ByVal e As System.EventArgs)
If TypeOf (sender) Is ComboBox Then
Dim cboThisCombobox = DirectCast(sender, ComboBox)
RemoveHandler cboThisCombobox.SelectedValueChanged, LastEventHandler
End If
End Sub
来源：https://stackoverflow.com/questions/582625/editingcontrolshowing-events-firing-multiple-times