Visual Basic

4-Mar-07 0:20

I've been messing around with CodeDom lately in an attempt to generate some data handling code for my latest project and run into a problem that has me stumped. It seems that when generating an If statement in VB .NET and calling the IdentityInequality operator you get different results when you would expect the operator to act in a consistent manner.

I have the following snippet of code:

Dim csIfStatement As CodeConditionStatement<br />
        Dim csDBNullIfStatement As CodeConditionStatement<br />
<br />
        ...<br />
<br />
            csIfStatement = New CodeConditionStatement(New CodeBinaryOperatorExpression(New CodeVariableReferenceExpression("drData"), CodeBinaryOperatorType.IdentityInequality, New CodePrimitiveExpression(Nothing)))<br />
<br />
            For Each row As DataRow In Me._Columns.Rows<br />
                strColumnName = row("COLUMN_NAME").ToString()<br />
<br />
                csDBNullIfStatement = New CodeConditionStatement(New CodeBinaryOperatorExpression(New CodeMethodInvokeExpression(New CodeVariableReferenceExpression("drData"), "Item", New CodePrimitiveExpression(strColumnName)), CodeBinaryOperatorType.IdentityInequality, New CodePropertyReferenceExpression(New CodeTypeReferenceExpression("DBNull"), "Value")))<br />
<br />
                csDBNullIfStatement.TrueStatements.Add(New CodeAssignStatement(New CodeVariableReferenceExpression("_" + strColumnName), New CodeMethodInvokeExpression(New CodeVariableReferenceExpression("drData"), "Item", New CodePrimitiveExpression(strColumnName))))<br />
<br />
                csIfStatement.TrueStatements.Add(csDBNullIfStatement)<br />
            Next<br />
<br />
            cmMethod.Statements.Add(csIfStatement)<br />
<br />
        ...

Which gives me the following output:

If (Not (drData) Is Nothing) Then<br />
    If (drData.Item("JobID") <> DBNull.Value) Then<br />
        _JobID = drData.Item("JobID")<br />
    End If<br />
End If

When I really want:

If (Not (drData) Is Nothing) Then<br />
    If (Not drData.Item("JobID") Is DBNull.Value) Then<br />
        _JobID = drData.Item("JobID")<br />
    End If<br />
End If

Has anyone been in the same situation or know how I get around this? I'm sure I'm just too much of a noob at this and have missed something very basic.

Thanks

Simon

Dave Kreskowiak4-Mar-07 3:33

Re: CodeDom IdentityInequality Problem [modified]

4-Mar-07 3:33

I may be wrong here, because I don't write this kind of code, but IIRC, the Is operator is a VB.NET shortcut for comparing the type references of two objects. I think you're missing getting the CodeTypeReference of both operands.

My confidence level on this answer is about 10%, so feel free to ignore this! :->

Dave Kreskowiak
Microsoft MVP - Visual Basic

simonh234-Mar-07 12:47

4-Mar-07 12:47

Hi Dave

Thanks for this.

I'll give it a go and see how it reacts, I think I might still have an issue though because when I change the operator from IdentityInEquality to IdentityEquality I do get an Is instead of an =. So the problem just seems to be isolated to the IdentityInEquality operator. I was thinking that it might have something to do with there not being a ValueInequality operator, maybe someone tried to get funky and combine the two with some smarts??

Simon

-- modified at 22:42 Sunday 4th March, 2007

Dave Kreskowiak5-Mar-07 3:23

5-Mar-07 3:23

I think you were on the right track with this one. Now all you have to do is get a Not operator in front of the binary expression and you should be OK.

Dave Kreskowiak
Microsoft MVP - Visual Basic

simonh235-Mar-07 22:40

5-Mar-07 22:40

Hi Dave

I know I can just "hard code" it in the generation methods to give me the VB syntax I want, but I was wondering if there was an answer that would allow me to port it to C# if I needed to in the future without having to recode that part... The more I look at it it seems to be a Microsoft quirk that you just have to put up with when you use their stuff.

Thanks for trying Smile | :)

Simon

simonh234-Mar-07 23:56

4-Mar-07 23:56

Just an update, I tried the above suggestion and have had no luck. The generated code now comes out as:

<br />
If (drData.Item("JobID").GetType <> GetType(DBNull)) Then<br />
     _JobID = drData.Item("JobID")<br />
End If

When it should be:

If (Not drData.Item("JobID").GetType Is GetType(DBNull)) Then<br />
     _JobID = drData.Item("JobID")<br />
End If

So no luck with that one... Thanks for the attempt though, thought you might have been on the right track there.

Simon

Usercontrol on MDI Form

jazzyjboombox3-Mar-07 22:18

jazzyjboombox

3-Mar-07 22:18

Hi,

Is it possible in VB.net to add a usercontrol onto a form that is set as IsMDIContainer? I can successfully add the control onto the MDI form but am having problems showing Child forms when the user clicks a button on the usercontrol.

The below code is run when the menu's button is clicked, basically creates and instance of the form, sets the size equal to a size area where I want child forms to take up, shows the form and brings it to front.

Private Sub Menu1_ButtonClicked(ByVal Index As Integer) Handles Menu1.ButtonClicked
Select Case Index
Case 1
Dim objForm As New frmClients
objForm.Size = Menu1.FormArea
objForm.Show()
objForm.BringToFront()
End Select
End Sub

In the New() method of the form being shown is the following code which assigns the mdiparent window property and adds the form into a collection so it does not go out of scope.

Me.MdiParent = Application.MainWindow
Application.Forms.Add(Me)

There isn't an issue with child forms showing as the application worked ok before, it is only since adding the usercontrol and trying to load forms via this control.

Cheers
Big Grin | :-D

Dave Kreskowiak4-Mar-07 3:18

4-Mar-07 3:18

Your usercontrol shouldn't be concerned with creating new forms and assigning them to a parent. This would tie your usercontrol to the form, and application, to the point where you couldn't possibly use the control in any other form or application.

There is no problem with putting a usercontrol on an MDIParent form, so long as you understand how an MDIParent form renders it's contents. In the client area of an MDIParent, it's the same as any other form. You drop controls on it and they'll show up. But, there is a control that takes up the entire client area of an MDIParent form, called the MdiClient control. This control is what your MDIChild forms get shown by.

The MdiClient control is normally sitting behind all the other controls on the MDIParent form. It'll appear as if all of your MDIParent controls are hovering over all of your MDIChild forms.

Now, as far as manage MDIChildren, the parent form should be doing that, not your usercontrol. You control should be written to expose an event that the MDIParent subscribes to and is told that a new MDIChild form should be created. Your MDIParent then has the option of ignoring this request or following through with it. Then, creating the child form is easy:

Dim newChild As New Form2
newChild.MdiParent = Me
newChild.Show()

Dave Kreskowiak
Microsoft MVP - Visual Basic

jazzyjboombox4-Mar-07 21:10

jazzyjboombox

4-Mar-07 21:10

Hi Dave,

Thanks for your reply.

My usercontrol doesn't actually create and load forms. It raises an event that passes and index representing the button that is clicked on the control. My problem seems to be that the usercontrol seems to stay at front and the forms that get loaded are hidden behind. After clicking the button which loads a form I hid the usercontrol and I could then see the form?

In the code I do try to bring the loaded form to front - objForm.BringToFront() but this doesn't seem to work.

Does anything obvious stand out in my logic?

Thanks again for your time.

Regards

David
Wink | ;)

;);)

Dave Kreskowiak5-Mar-07 3:21

5-Mar-07 3:21

You missed the point of my reply entirely. Your MDIChild IS in front...of all other MdiChildren.

The problem is that all MDIChildren are rendered by the MdiClient control, which is BEHIND your UserControl. Your MdiParent has TWO controls on it, not one. The MdiClient control (which hold all of your MdiChild forms) and your UserControl. Calling BringToFont on the MDIChild form only brings it to the front of the stack of MDIChild forms INSIDE the MdiClient control.

You have to call BringToFront on the MdiClient control, or call SendToBack on your UserControl. But, that'll make your UserControl appear to disappear, when really, it's behind the MdiClient control.

Dave Kreskowiak
Microsoft MVP - Visual Basic

jazzyjboombox5-Mar-07 10:27

jazzyjboombox

5-Mar-07 10:27

Thanks Dave, will try to come up with a better solution than creating a user control for my purposes.

Thanks again for your time.

Regards

David Smile | :)

data transfer into excel

amaneet3-Mar-07 19:04

Re: data transfer into excel

3-Mar-07 19:04

sir/madam,
i have data in the table and database(MS-Access) .Can i send the data into excel sheet.
please help.
thanks and regards
pankaj garg

Vasudevan Deepak Kumar4-Mar-07 17:12

Vasudevan Deepak Kumar

4-Mar-07 17:12

Did you try the DTS Wizard?

Vasudevan Deepak Kumar
Personal Homepage
Tech Gossips

Re: data transfer into excel

prakash J9-Mar-07 2:32

prakash J

9-Mar-07 2:32

just select the tabel tht u want in excel and u can see a icon called office links there will be 2 optons for word and excel just select excel
the total datas in that selectd tabel will display in excel

Cheers

Prakash

referential classes

amaneet3-Mar-07 19:00

3-Mar-07 19:00

sir/madam,
can i please get to know about the referential classes.
thanks and regards
pankaj garg

Guffa4-Mar-07 2:04

Guffa

4-Mar-07 2:04

Look under reference types:
http://www.devx.com/enterprise/Article/28246[^]

---
single minded; short sighted; long gone;

Christian Graus4-Mar-07 2:13

Christian Graus

4-Mar-07 2:13

All classes are passed by reference, structs are passed by value. Is this what you meant ?

Christian Graus - Microsoft MVP - C++
Metal Musings - Rex and my new metal blog
"I am working on a project that will convert a FORTRAN code to corresponding C++ code.I am not aware of FORTRAN syntax" ( spotted in the C++/CLI forum )

amaneet4-Mar-07 2:33

4-Mar-07 2:33

No Sir
I was trying the compression program
like in C++ storing the address of another variable.
I am now trying to store the address of another variable in vb.net
Please help.
Thanks and regards
Pan

Dave Kreskowiak4-Mar-07 3:09

4-Mar-07 3:09

amaneet wrote:
I am now trying to store the address of another variable in vb.net

In the world of Managed code, the address of a variable doesn't really exist the way it does in unmanaged C++. Any object or piece of code can be moved at any time, thereby invalidating any stored address you have on it. Addresses to code (function pointers) are handled by delegates in the .NET Framework. Variables are passed by reference, but that's not an address in the C++ sense of the word.

What are you trying to do with this?

Dave Kreskowiak
Microsoft MVP - Visual Basic

amaneet4-Mar-07 3:25

4-Mar-07 3:25

Sir
i meant that can i implement the double link list in vb.net
Please provide help.
Thanks and Regards
Pankaj

Dave Kreskowiak4-Mar-07 11:03

4-Mar-07 11:03

You can find a doubly-linked list implementation right here[^] on CP. It's written in C#, but is easily convertible to VB.NET if you want.

Dave Kreskowiak
Microsoft MVP - Visual Basic

interface problem

amaneet3-Mar-07 18:58