sender question

[kleinma]

I have a 3 checkboxes and a sub that handles all 3 of their CheckChanged events. Basically I need to prevent them from unchecking ALL as at least 1 needs to be checked. When they uncheck the lasted checked box it will give a messagebox stating they need to select at least 1, and i want it to recheck the one they just unchecked. I imagine I would be able to reference it via the sender object passed in, but I am having a hard time figuring out how to reference this to the checkbox itself?

I got this code to work, but im not sure if I NEED to actually create a new object to accomplish this

MessageBox.Show("At least 1 checkbox must be checked", "ERROR", MessageBoxButtons.OK, MessageBoxIcon.Error)
            Dim MyCheck As New CheckBox
            MyCheck = CType(sender, CheckBox)
            MyCheck.Checked = True
            MyCheck = Nothing

is this efficient?

[Mike Hildner]

I'm not smart enough to know whether this is more effecient or not, but you can also do it like this:

CType(sender, CheckBox).Checked = True

What I don't know is if that's any different or not. I mean, does that act on the sender object itself, or does CType create a new object. If it does, I guess it would not be more effecient than your code, but it is less typing.

Mike

[kleinma]

more importaintly, if it DOES create an instance... does it destroy it as well?

[Mike Hildner]

I *guess* it does create an object. MSDN says "Returns the result of explicitly converting an expression to a specified data type, object, structure, class, or interface".

Also guessing (big help here, huh?) that once it goes out of scope, it's eligible for GC. In that case, there's no variable to set to Nothing.

[Mike Hildner]

Not sure if this would be considered bad code or not, but this works just fine:

Private Sub CheckBox1_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CheckBox1.CheckedChanged
        sender.Checked = True
    End Sub

[TLord]

Try this:

Sub CheckedChanged(ByVal Sender As Object, ByVal e As System.EventArgs) Handles CBx1.CheckedChanged, CBx2.CheckedChanged, CBx3.CheckedChanged
  If Not (CBx1.Checked Or CBx2.Checked Or CBx3.Checked) Then
    MessageBox.Show("...")
    CType(sender, CheckBox).Checked = True
  End If
End Sub

Mike Hildner's first reply was good, but he went backwards at this last reply becsue Option Strickt On disallows late binding.

[nemaroller]

No need for expensive CTYPE operation. You will always be passed a checkbox, so
no need for Ctype.

'this only assigns a reference to 
'the sending object
'but lets the compiler
'know that it will always
'be a checkbox
 
Dim myCheckBox As CheckBox = DirectCast(sender, CheckBox)
 
'or
DirectCast(Sender,CheckBox).Checked=True

[kleinma]

Originally posted by nemaroller
No need for expensive CTYPE operation. You will always be passed a checkbox, so
no need for Ctype.

'this only assigns a reference to 
'the sending object
'but lets the compiler
'know that it will always
'be a checkbox
 
Dim myCheckBox As CheckBox = DirectCast(sender, CheckBox)
 
'or
DirectCast(Sender,CheckBox).Checked=True

thanks for the input, ill use the directcast method

[taxes]

Originally posted by Mike Hildner
Not sure if this would be considered bad code or not, but this works just fine:

Private Sub CheckBox1_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CheckBox1.CheckedChanged
        sender.Checked = True
    End Sub

This wont work with Option Strict On