Visual Basic

26-Jul-09 10:18

I cannot figure out why this doesn't work. Everythign says it should... I'm trying to see if a datagridviewrow contains DBNUll

'first = IIf(TypeOf _row.Cells(1).Value Is DBNull, 0, CDec(_row.Cells(1).Value))
'second = IIf(TypeOf _row.Cells(2).Value Is DBNull, 0, CDec(_row.Cells(2).Value))
'final = IIf(TypeOf _row.Cells(3).Value Is DBNull, 0, CDec(_row.Cells(3).Value))

I GET ERRORS!!!

But if I do this, not only is it ugly as heck but it works!!

If (TypeOf _row.Cells(1).Value Is DBNull) Then
    first = 0
Else
    first = _row.Cells(1).Value
End If

If (TypeOf _row.Cells(2).Value Is DBNull) Then
    second = 0
Else
    second = _row.Cells(2).Value
End If

If (TypeOf _row.Cells(3).Value Is DBNull) Then
    final = 0
Else
    final = _row.Cells(3).Value
End If

Why?!?! I'm so angry. I have tried everything from

IsDBNull(value)

value Is DbNull
value Is DbNull.Value

value is typeof(DbNull)

Its just frustating.. am I doing something wrong here or is this just a flaw?

Mycroft Holmes26-Jul-09 12:24

Mycroft Holmes

26-Jul-09 12:24

Yah I knew I used it somewhere, try

mvLogID = IIf(IsDBNull(oRow("LogID")), 0, oRow("LogID"))

Never underestimate the power of human stupidity
RAH

Jacob Dixon26-Jul-09 14:51

26-Jul-09 14:51

No luck. I'm not trying to find if a row is null, just if a cell is null

first = IIf(IsDBNull(_row.Cells(1)), 0, CDec(_row.Cells(1).Value))
second = IIf(IsDBNull(_row.Cells(2)), 0, CDec(_row.Cells(2).Value))
final = IIf(IsDBNull(_row.Cells(3)), 0, CDec(_row.Cells(3).Value))

Using the name instead of the index doesn't work either.
Still get "Conversion from DBNull to type Decimal is not valid"

Mycroft Holmes26-Jul-09 14:59

Mycroft Holmes

26-Jul-09 14:59

Can I have my foot back now please Blush | :O

I was testing against a DATAROW.
Try, you are testing the cell, it will always be there. And here is your foot Big Grin | :-D

first = IIf(IsDBNull(_row.Cells(1).Value), 0, CDec(_row.Cells(1).Value))

Never underestimate the power of human stupidity
RAH

Jacob Dixon26-Jul-09 15:04

26-Jul-09 15:04

Lol

Still no luck though. Here it is:

(All of it)

For Each _row As DataGridViewRow In dgvGrades.Rows
                Dim first, second, final As Decimal

                ' ********* This doesnt not seem to work but technically it should **************
                ' ********* Must be a FLAW in VB.net :-) lol ************
                'first = IIf(TypeOf _row.Cells(1).Value Is DBNull, 0, CDec(_row.Cells(1).Value))
                'second = IIf(TypeOf _row.Cells(2).Value Is DBNull, 0, CDec(_row.Cells(2).Value))
                'final = IIf(TypeOf _row.Cells(3).Value Is DBNull, 0, CDec(_row.Cells(3).Value))

                first = IIf(IsDBNull(_row.Cells(1).Value), 0, CDec(_row.Cells(1).Value))
                second = IIf(IsDBNull(_row.Cells(2).Value), 0, CDec(_row.Cells(2).Value))
                final = IIf(IsDBNull(_row.Cells(2).Value), 0, CDec(_row.Cells(3).Value))

                Dim _average As Decimal = (first + second + 2 * final) / 4

                For Each _sRow As DataGridViewRow In dgvStudents.Rows
                    If _row.Cells(0).Value Is Nothing Then
                        Exit For
                    Else
                        If _row.Cells(0).Value = _sRow.Cells(0).Value Then
                            dgvAverage.Rows.Add(New Object() {_sRow.Cells(2).Value.ToString() + " " + _sRow.Cells(1).Value.ToString(), _average.ToString(), CalculateGrade(_average), IIf(_average > 59, True, False)})
                            Exit For
                        End If
                    End If
                Next
            Next

The funny thing is (well not so funny) is that I can do this:

If IsDBNull(_row.Cells(1).Value) Then
MessageBox.Show("IT IS NULL!")
End If

AND IT WORKS! its the same thing!

nlarson1126-Jul-09 16:24

nlarson11

26-Jul-09 16:24

you said "you get errors". what error are you getting?

btw...not sure if you meant to do this but you are testing cell 2 again and then useing cell 3

final = IIf(IsDBNull(_row.Cells(2).Value), 0, CDec(_row.Cells(3).Value))

'Never argue with an idiot; they'll drag you down to their level and beat you with experience.' ~ anonymous

'Life's real failure is when you do not realize how close you were to success when you gave up.' ~ anonymous

Jacob Dixon26-Jul-09 16:28

26-Jul-09 16:28

The error is it can't convert dbnull to decimal. It shouldn't be trying because it's supposed to make it 0 if it was dbnull. Yeah I didn't mean to do that I just changed it so much trying to get it to work I messed that up

nlarson1126-Jul-09 16:35

nlarson11

26-Jul-09 16:35

I have seen that somestimes checking for dbnull in an IIF doesn't always work. try breaking it out into a normal IF/Else statement.

Jacob Dixon26-Jul-09 17:15

26-Jul-09 17:15

Well I know that it works fine with a bunch of if then statements.

I was trying to figure out if it was something I was doing why the IIf wasn't working. But its starting to look more like a flaw with VB.net. Using the IIf statements looks much cleaner and less code to me. But if it just won't work with comparing DBNull values.. then what can I do lol

nlarson1127-Jul-09 3:03

nlarson11

27-Jul-09 3:03

ya it's a bug...

you can get the same effect by writing a function that will act like the IIF so you'll get the clean look but the function will use the full if/then/else...

't = true part of iif / e = else part of iif
public function MyIIF (b as boolean, t as object, e as object) as object

you can of course overload that to do type-safe checks

public function MyIIF (b as boolean, t as string, e as string) as object
public function MyIIF (b as boolean, t as integer, e as integer) as object

etc

Jacob Dixon27-Jul-09 3:07

27-Jul-09 3:07

Ok Thanks for your help Smile | :)

Jack Vanderhorst27-Jul-09 4:37

Jack Vanderhorst

27-Jul-09 4:37

If you're using VB9 there is an overload for the If keyword that solves this problem.

Instead of IIf try just using If

Dougie the P5-Aug-09 18:07

Dougie the P

5-Aug-09 18:07

When using IIF both the true and the false portions are evaluated before the IIF test is done.

using the If construct only the true portion is evaluated after the IF test is done and the false portion is never evaluated if the test is true.

which is faster?

TheMrProgrammer25-Jul-09 19:00

TheMrProgrammer

25-Jul-09 19:00

Hi
In my app i have to read thousands of lines of data written in a
text file.
I have saved the lines previously.
The size of text file is 50 MB.

My problem is that it takes a lot of time to read that.

If i save the lines in a database, would the 'reading' be faster?

TheMrProgrammer
http://www.icbse.com/2009/funny-exam-answers-school-students
http://download.cnet.com/TheCalcMan/3000-2094_4-10958266.html

Luc Pattyn25-Jul-09 22:34

Luc Pattyn

25-Jul-09 22:34

Hi,

I very much doubt reading 50MB of data is taking very long, it should be possible to do that in say 1 second. If your app is slower at it, it probably is due to what it is you do with the data, such as adding it to some of the GUI controls. Tell us more, and show some relevant code.

Smile | :)

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TheMrProgrammer26-Jul-09 5:08

TheMrProgrammer

26-Jul-09 5:08

Hi Luc,
Thanks for reply.

Yes I do more than reading.

I read the file.

Dim s$ = my...readalllines(myfile.txt)

There are sentences separated by # which I transfer in an array
so that one sentence get into one element of array
using simple code of 6 lines.
This operation I do in the variable s.

that's all I do.

The size of the testing file is 10 MB and it takes about 4 min and 24 s
The size of real file is nearly 50 MB.

So what do you suggest now?

TheMrProgrammer
http://www.icbse.com/2009/funny-exam-answers-school-students
http://download.cnet.com/TheCalcMan/3000-2094_4-10958266.html

Luc Pattyn26-Jul-09 8:41

Luc Pattyn

26-Jul-09 8:41

Prankur Rusia wrote:
So what do you suggest now?

Huh? The same as I suggested some 10 hours ago. You haven't given any new facts.

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

The quality and detail of your question reflects on the effectiveness of the help you are likely to get.
Show formatted code inside PRE tags, and give clear symptoms when describing a problem.