How to prevent Checkbox Checkchanged event from firing in VB.Net - vb.net

Question

I have this code in my one function
If DataServices.IsGroupByMe(test) = True Then
chkGroup.Visible = True
chkGroup.Checked = True
Else
chkGroup.Checked = False
chkGroup.Visible = False
End If
Upon going through this line
chkGroup.Checked = True
It automatically calls my checkchanged event for that checkbox
Private Sub chkGroupByMe_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles chkGroupOper.CheckedChanged
LoadFilteredData()
End Sub
Which then distrupts the usual sequence of action to perform. Are there ways to prevent triggering the checkchanged event?
Please note that the first function in the base form. and the checkchanged event in a different child form inheriting the base.

Answer 1

You can simply use a variable to block the update:
private bool PreventUpdate;
// your function
If DataServices.IsGroupByMe(test) = True Then
PreventUpdate = true;
// ... all tasks
PreventUpdate = false;
// handler
Private Sub chkGroupByMe_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles chkGroupOper.CheckedChanged
if not PreventUpdate Then
LoadFilteredData()
End Sub

Answer 2

A simple method would be to remove the Event Handler before settings its value and then re-assigning it.
Before setting the checked value (or at the start of the function):
RemoveHandler chkGroup.CheckedChanged, AddressOf chkGroupByMe_CheckedChanged
And after setting the checked value (or at the end of the function):
AddHandler chkGroup.CheckedChanged, AddressOf chkGroupByMe_CheckedChanged
Note: Anytime you add an EventHandler using the method above, always make sure there is a corresponding RemoveHandler called before it. Calling RemoveHandler too many times won't be a problem, but having your events handled too many times will cause you a few headaches wondering what is going on.

Answer 3

This is tough to answer since we don't really know the structure of your forms, in which form each piece of code reside nor how you interact with them.
However, one option is that you create a Shared property in the base form that indicates when LoadFilterData() should be bypassed.
Put this in your base form:
Protected Shared Property BypassDataLoad As Boolean = False
Then in your function do:
If DataServices.IsGroupByMe(test) = True Then
BaseForm.BypassDataLoad = True
chkGroup.Visible = True
chkGroup.Checked = True
BaseForm.BypassDataLoad = False
Else
BaseForm.BypassDataLoad = True
chkGroup.Checked = False
chkGroup.Visible = False
BaseForm.BypassDataLoad = False
End If
...and in your event handler:
Private Sub chkGroupByMe_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles chkGroupOper.CheckedChanged
If Not BaseForm.BypassDataLoad Then
LoadFilteredData()
End If
End Sub
Replace BaseForm with the actual name of your base form class.

Answer 4

you can remove the event handler using RemoveHandler before setting the Checked property to true. Then in the else case where you set the Checked property to false you can add the eventhandler back using the AddHandler. so that whenever it is checked the actual event will fire.

Answer 5

You can use the "Tag" property of the checkbox in order to control the "CheckChanged" event instead of removing and re-adding the handler again.
Please try the following code:
If DataServices.IsGroupByMe(test) Then
chkGroup.Tag = "0"
chkGroup.Visible = True
chkGroup.Checked = True
Else
chkGroup.Tag = "0"
chkGroup.Checked = False
chkGroup.Visible = False
End If
Private Sub chkGroupByMe_CheckedChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles chkGroupOper.CheckedChanged
If chkGroup.Tag <> "0" Then
LoadFilteredData()
End If
chkGroup.Tag = ""
End Sub