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Question
Tuesday, November 13, 2007 11:00 PM
Hi there... I'd like to temporarily disable events for a given control. For example, the SelectionChanged event on a combobox might be used to update a display every time the user changes the combobox... but while I'm filling the combobox with values, I don't want the SelectionChanged event to be firing over and over... I need to disable events while the combobox is being populated. How do I do this?
WATYF
All replies (13)
Wednesday, November 14, 2007 7:58 PM ✅Answered
The best way I've found to do this is to use a class-scope flag variable that is checked at the start of every control event you want to keep from firing. It's kind of a pain but it does work well - especially when you are doing a cluster of settings like populating a form's controls with data. By not including the bypass then you can be sure that certain events do fire every time. Also, in teh case of teh combobox you can use the SelectionChangeCommitted event becuase it only fires off when the user selects an item from the list (not when you do it programmatically).
Code Block
Public Class Form1
Private ControlBypass As String = False
Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) _
Handles ComboBox1.SelectedIndexChanged
If ControlBypass Then Return
If ComboBox1.SelectedIndex > 0 Then
ControlBypass = True
ComboBox1.SelectedIndex -= 1
ControlBypass = False
End If
End Sub
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
For x As Int32 = 0 To 5
ComboBox1.Items.Add("Item " & x)
Next
End Sub
End Class
Tuesday, November 13, 2007 11:24 PM
This should work:
To lock the control.
ComboBox1.Enabled = False
To unlock it again.
ComboBox1.Enabled = True
hth,
Olice
Wednesday, November 14, 2007 6:06 PM
Really? I did not know that disabling a control turned off it's events. I will try that. Thanks.
WATYF
Wednesday, November 14, 2007 7:00 PM
***... that didn't work. The event still fires. Any other ideas?
WATYF
Wednesday, November 14, 2007 7:29 PM
I placed a combobox on a form and used ocertain's code like so, and it worked just fine:
Code Block
Public Class Form1
Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
MsgBox("changed")
End Sub
Private Sub LoadCombo()
For i As Integer = 0 To 9
Me.ComboBox1.Items.Add("Item " & i)
Next
End Sub
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
Me.ComboBox1.Enabled = False
LoadCombo()
Me.ComboBox1.Enabled = True
End Sub
End Class
could you post the code of what you're trying to do?
Wednesday, November 14, 2007 7:32 PM
Yeah, sorry... I said "load the combobox", but technically "loading" items into it isn't what fires the event. After the load is done, I select the topmost item in the combobox (so it's not set to nothing). When I do that, then the event fires.
WATYF
Thursday, November 15, 2007 6:49 PM
Yeah, I've always used a public variable to accomplish this type of thing... I was just wondering if there was a cleaner way to do it. It looks like there isn't, though, so I just went back to using a variable flag.
WATYF
Thursday, November 15, 2007 6:58 PM
I suppose if you were to use custom controls that implement an interface with a Bypass property or just plain have the property then you could use those controls instead of the standard ones. You should still be able to plop on to the designer as User Controls like any other control.
Wednesday, August 13, 2008 4:39 PM
Although using a public variable will solve custom issues, it won't help for generic solutions. For example if you have a combobox listing customers which is used in lots of different forms in a project and call a child form to allow user to change customer information and go back to parent form containing the combobox you'll need to clear and refill the contents of combobox as the user probably changes some data that will effect the appearance of data in combo. You need to exactly know which form the call was made and this is something messy. So you can try something else in these situations. You can use the TAG property of combobox to communicate with calling form with combobox so that when the tag property is set to true you can exit the SelectedIndexChanged subroutine. When the child form needs to refill the combobox all it has to do is setting the tag value to true during operation and false when done. Here is an example:
| If Not IsNothing(Me.Owner) Then |
| Dim tbMusteriler As DataTable, rowSatir As DataRow, foUstForm As Form, iKodMusteri As ComboBox, coKontrol As Control |
| Dim obEleman As clListeEleman |
| 'Open table - it uses a function i wrote, you can use your own method, it is irrelevant |
| tbMusteriler = TabloAc("SELECT * FROM tbMusteriler WHERE bTip=0 ORDER BY sUnvan", Me.Owner) |
| foUstForm = Me.Owner.ActiveMdiChild 'This code runs on a project with a main page of MDI parent. That's why it refers to ActiveMDIChild. You can change this according to your form hierarchy |
| coKontrol = foUstForm.Controls.Find("iKodMusteri", False)(0) 'Find the combobox to refill |
| iKodMusteri = CType(coKontrol, ComboBox) |
| iKodMusteri.Tag = True 'Set tag to true to stop SelectedIndexChangedEvent of combo |
| iKodMusteri.SuspendLayout() 'Optional, irrelevant |
| iKodMusteri.Items.Clear() |
| iKodMusteri.Text = "" |
| For Each rowSatir In tbMusteriler.Rows |
| obEleman = New clListeEleman(rowSatir("sUnvan"), rowSatir("aKod")) 'Use a class to add value-text members |
| iKodMusteri.Items.Add(obEleman) |
| If rowSatir("aKod") = vKodMusteri Then 'If current item is equal to the record currently being edited, select it. vKodMusteri is a public variable defined at top of that form's code and is set to combobox's selected value |
| iKodMusteri.SelectedIndex = iKodMusteri.Items.Count - 1 |
| iKodMusteri.Text = rowSatir("sUnvan") |
| End If |
| Next |
| iKodMusteri.ResumeLayout() |
| iKodMusteri.Tag = False 'Set tag to false to enable SelectedIndexChangedEvent |
| End If |
And here is the SelectedIndexChanged code of combo
| Private Sub iKodMusteri_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles iKodMusteri.SelectedIndexChanged |
| If iKodMusteri.Tag = True Then Exit Sub 'When tag property is set to true by the code above, this line will exit the sub without executing the code below |
| . |
| . Your code to be run when selected index is changed |
| . |
| End Sub |
Wednesday, August 13, 2008 4:58 PM
Hi
You can disable events to the combobox by doing the following; i presume you have a bindingsource bound to the combobox
Me
.bindinsource.RaiseListChangedEvents = false
then
Me**.bindinsource.RaiseListChangedEvents = TRUE
**
Thanks
G Rusher
Wednesday, August 13, 2008 8:11 PM
Good Idea G Rusher. For that matter you could use the SuspendBinding and resumeBinding properties on teh binding source to accomplish the same goal. I haven't tried it but it might work here.
Yalin: Using the Tag property is just a notch better than using a public variable -- at least it's tied to a specific control -- but it still falls in the category of what the OP was trying to avoid. This is why my original advice wasn't really the ideal solution either.
Monday, August 23, 2010 12:42 PM
Thanx,
You given a great solution.
Sunday, November 17, 2019 12:38 PM | 1 vote
Disabling ComboBox (see ocertain's post above) almost works.
The event will still fire, but nothing will happen if you wrap your code (in the sub that is called when the event fires) within an if clause:
If .ComboBox.Enabled then
End if
Kinda like the public variable or tag solutions, but cleaner.