Problem with DataGrid

[mjb3030]

I am completely stumped.

 

I have a datagrid that is acting very strangely. The following method handles the ColumnChanging event of the underlying table:

 

   Private Sub tbl_ColumnChanging(ByVal sender As Object, _
        ByVal e As System.Data.DataColumnChangeEventArgs) Handles _
        tbl.ColumnChanging

       If Not IsNumeric(e.ProposedValue) Then
           e.Row.SetColumnError(e.Column, "You must enter a number")
           Exit Sub
       End If
       If AlreadyChecked(dgrData.CurrentCell.RowNumber, dgrData.CurrentCell.ColumnNumber) Then
           Exit Sub
       End If
       AlreadyChecked(dgrData.CurrentCell.RowNumber, dgrData.CurrentCell.ColumnNumber) = True
       Dim LastPoint As Int16

       ' The TreadData class simply returns an OLEDBDataReader
       ' when I pass it an SQL statement. It works fine throughout
       ' the rest of my program.
       Dim tdMaxPoints As TreadData = New TreadData("SELECT MAX(Point_ID) AS MaxPointID " & _
           "FROM Points INNER JOIN " & _
           "(Grooves INNER JOIN (Tires INNER JOIN Tests ON Tires.Test_ID = " & _
           "Tests.Test_ID) ON Grooves.Tire_ID = Tires.Tire_ID) ON Points.Groove_ID " & _
           "= Grooves.Groove_ID WHERE GrooveNumber = " & dgrData.CurrentCell.RowNumber - 1 & " AND " & _
           "PointNumber = " & dgrData.CurrentCell.ColumnNumber)
       While tdMaxPoints.TreadReader.Read
           Dim tdPoints As TreadData = New TreadData("SELECT Measure FROM Points " & _
               "WHERE Point_ID = " & tdMaxPoints.TreadReader("MaxPointID"))

           ' Right after the previous line, before the next line, my code
           ' jumps back to the beginning of this method.

           While tdPoints.TreadReader.Read
                'Do Stuff
           End While
   End Sub

 

At the point I indicated in the code, my app jumps back to the beginning of that method. Apparently, the underlying table changes in the middle of the ColumnChanging event?! When I check the proposedvalue on the second pass through, it shows an empty string instead of the value that had been entered.

 

The only thing I could think of was another thread changing something. I have one other thread running which is listening for input from the serial port. But, I tried disabling that thread, and I got the same behavior.

 

I also am experiencing strange behavior with the method that is handling the Enter event for all of the textboxes on my datagrid. I think this may be related. If I put an 'Exit Sub' at the beginning of the ColumnChanging event so as to bypass it, the TextBox_Enter method exhibits the following behavior: It will perform the method twice for each textbox. But, only if I have changed a value in the previous textbox. In other words, only when the ColumnChanging event occurs. If I tab to another textbox without changing the value, the Enter event only happens once.

 

   Private Sub dgrData_TextBox_Enter(ByVal sender As Object, ByVal e As _ EventArgs)
       If dgrData.CurrentCell.ColumnNumber = dsMeasures.Tables(0).Columns.Count - 2 And _
           dgrData.CurrentCell.RowNumber = dsMeasures.Tables(0).Rows.Count - 1 Then
           btnDone.Focus()
           Exit Sub
       ElseIf dgrData.CurrentCell.ColumnNumber = dsMeasures.Tables(0).Columns.Count - 2 Or _
           dgrData.CurrentCell.ColumnNumber = dsMeasures.Tables(0).Columns.Count - 1 Then
           Dim r As Int16 = dgrData.CurrentCell.RowNumber
           dgrData.CurrentCell = New DataGridCell(r + 1, 1)
       ElseIf dgrData.CurrentCell.ColumnNumber = 0 Then
           Dim r As Int16 = dgrData.CurrentCell.RowNumber
           dgrData.CurrentCell = New DataGridCell(r, 1)
       ElseIf dgrData.CurrentCell.RowNumber > NumGrooves - 1 Then
           dgrData.CurrentCell = New DataGridCell(dsMeasures.Tables(0).Rows.Count - 1, 1)
       End If
   End Sub

 

Any thoughts?

[AlexCode]

Damn dude... too many lines at this point for me to evaluate... sorry.

 

What I have to say to you is:

 

Your thread header: "Problem with DataGrid"

- No man... that's wrong... the Datagrid itself is a/the problem... throw it off for god sake... :D

Your first statement: "I am completely stumped."

Yeah ... you and a few more milions programmers that're still using datagrid...

 

:D I'm joking but... saying the truth...

 

As a helper for you it would worth a look at http://dotnet.leadit.be/extendeddatagrid/

This is a nice, free, DataGrid extension if you don't want to spend some money on something good... (I can't open it, don't know if it's only down or actually gonne! :( still I leave you my last download of it...)

 

Alex :p

Leadit.ExtendedDataGrid_0_1_2_2_for_1_0.zip

[mjb3030]

Thanks. I appreciate it. I will check this out.

 

I decided to use textboxes for my current problem instead of a datagrid because I have a fixed number of rows and columns. I was just hoping the datagrid would make things a little easier. I still haven't figured out why the column data would change in the middle of the ColumnChanging event handler.

 

Maybe the .NET 2.0 datagrid will be the cure for our ailments.

[samsmithnz]

What does your alreadychecked function do? If you update your column in the middle of a column_changed event, you could be spawning another column change event....

[AlexCode]

Hi again...

 

I still haven't figured out why the column data would change in the middle of the ColumnChanging event handler.

I don't know either since I don't use the datagrid, but when something like that occurs we can set a flag to protect howr evet code.

This means that you can create a boolean var that states if the code is to be runned or not... something like:

 

dim flag as boolean = true 'True = Run code / False = Don't Run Code

...

Private sub myEvent...

If flag then

flag = false

 

'*** your code ***

 

flag = true

end if

End Sub

 

This way, even if the same event is called while it's running it doesn't repeat the same code...

 

This isn't even a bad practice... it's something worst but... what a heck! :)

 

Alex :p

[mjb3030]

What does your alreadychecked function do?

 

AlreadyChecked is just an array of Boolean values that indicates whether a particular cell has already been validated. It does not change or even access any table data.