Problem updating value in a DataGrid cell. [Resolved]

[albertlse]

I have a DataGrid, which has 3 columns:
- Net Price
- Quantity
- Total Price


I want the DataGrid to act like this:
- Net Price is set.
- User enter Quantity.
- Total Price is calculated automatically (Net Price * Quantity).
- Total Price column will be updated automatically.


So I wrote the code like this:

'Calculate total price
    Private Sub DataGrid_CurrentCellChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DataGrid.CurrentCellChanged
        Dim intPreviousRow As Integer
        Dim intColumn As Integer = DataGrid.CurrentCell.ColumnNumber

        If DataGrid.CurrentCell.RowNumber <> 0 Then
            intPreviousRow = DataGrid.CurrentCell.RowNumber - 1
        Else
            intPreviousRow = DataGrid.CurrentCell.RowNumber
        End If

        Dim intTaken As Integer = DataGrid.Item(intPreviousRow, intColumn)
        Dim dblNetPrice As Double = DataGrid.Item(intPreviousRow, intColumn + 1)
        Dim dblTotalPrice As Double = intTaken * dblNetPrice
        DataGrid.Item(intPreviousRow, intColumn + 2) = dblTotalPrice
    End Sub

Everytime I enter the Quantity, this error message pops up:

"An unhandled exception of type 'System.ArgumentException' occurred in system.windows.forms.dll

Additional information: The ListManager's position must be equal to rowNum."

The error occurs at the last line:

DataGrid.Item(intPreviousRow, intColumn + 2) = dblTotalPrice

Why? I can't solve this. I think the code I wrote cannot work.
Can anyone help me to solve, or write a new code for this situation?


Another question, after I have edited the DataGrid, if I want to save it to the database, I need to execute the DataAdapter's Update Command, right?
So how to code for this? Can anyone show me?

Please guide. Thank you.

[Lunatic3]

You dotn have to write thant bunch of code for this, just:
Imagine you have columns Net,Quantitiy,and total in mytable. you can use:
mytable.Columns("Total").Expression="Net * Quantity"

I attached a sample for you. put the database in C:\ to work.

[albertlse]

I follow exactly what you did, and I added this code:

DistributeDataSet.Tables(0).Columns(7).Expression = "Taken * NetPrice"

But I get this error:

An unhandled exception of type 'System.Data.EvaluateException' occurred in system.data.dll
Additional information: Cannot perform '*' operation on System.String and System.String.

why? is there any solution?

Please guide once again. Thank you.

[Lunatic3]

Its seems that you have defined those fields "Taken" and "NetPrice" as Text in your database. Either change their datatype to Number or try changing them to Number in the expression.

[albertlse]

I have modify my Access Database file. I changed the datatype from "Text" to "Number", and it is working fine now.

Can I do it in another way? where the datatype in Access Database file remain as "Text", and change the datatype through coding in VB?

In VB, I try to add this line of code:

DistributeDataSet.Tables(0).Columns("TotalPrice").DataType = System.Double

But the last part "System.Double" seems to generate error:

'Double' is a type in 'System' and cannot be used as an expression.

How to correct this code?

I want to use this method because, my DataGrid shows those number like 89.50 as 89.5, 95.00 as 95. I want it to be exactly 2 decimal point all the time. And I do not want to change the structure of my Access Database file.

Please guide. Thank you.

[Lunatic3]

To overcome that error this code:

DistributeDataSet.Tables(0).Columns("TotalPrice").DataType = GetType(System.Double)

That changes the datatype of your dataset and you can have the database type remained as text. But I am not sure that wont cause you a problem.
Try modifying your expression. Some functions are valid in the expression. Try to see if CInt, or Cdbl are valid in the expression or not.

[albertlse]

i think i will change the datatype in Access Database file. because my database has data in it. and VB .NET does not allow me to change via VB coding. anyway thanks for your guidance.