datagridview bound to bindingsource: displaying both old values and the new values

[tutus]

Hi,

I bound datagridview to bindingsource. The bindingsource has its datasource a collection Called Rates which is a collection of Rate items.

The rate object has a property called VALUE. I need the user to be able to edit different values for the collection; However, on the datagridview, i need to keep displaying on one column called OldValue the existing Rate value before the change while allowing the user to edit that value in a second column called NewValue.

In other terms, One colum OldValue will keep the existing values from the DB before being edited by the user, this column OldValue is readonly. Another column NewValue will display, the 1st time, the old value from the DB (similar to OldValue when we do the Fetch from the DB), but it`s editable column, so the user can modify each value in the column NewValue without overriding OldValue cells.

For now, I bound both columns OldValue and NewValue to the same property VALUE of the Rate object,

The problem I am having now is: when the user edits NewValue column, the same newvalue is copied to the first column : OldValue. I want the OldValue column to keep displaying the oldvalues instead of the new ones.

Do you know pls how I can do that ?

Thank you

[stanav]

1. You may want to set the LastValue" column in the datagridview to readonly (so that the user can't change it)
2. After you populate the datatable and right before you bind it to your datagridview, you use addhandler to add the datatable.columnchanging event handler to it.

3. Handle the datatable.columnchanging event of the datatable bound to your datagridview

Private Sub dt_ColumnChanging(ByVal sender As Object, ByVal e As System.Data.DataColumnChangeEventArgs)
        If e.Column.ColumnName = "CurrentValue" Then
            e.Row("LastValue") = e.Row("CurrentValue")
        End If
    End Sub

Upon re-reading your post, I have a question: What type is the Rate object?
If it's a datatable, you need to add another column to it to store the OldValue, and then proceed as posted above.

If it's a custom type, you need to add another property to it for the OldValue. In the setter of the NewValue property, you simply assign the current value to OldValue before setting the passed in value to NewValue variable.

private _OldValue as sometype
Public ReadOnly Property OldValue() as sometype
      Get    
           Return _OldValue
      End Get
End Property
  

Private _NewValue as sometype
Public Property NewValue() as sometype
    Get
         return _NewValue
    End Get
    Set(Byval value as sometype)
         OldValue = _NewValue
        _NewValue = value
    End Set
End Property

[tutus]

Thank u,

The reason I did not use newvalue, oldvalue properties in my Rate object is there is another requirement where the number of columns for which we need to keep oldvalue and newvalue is about 5 or 6 columns. I mean we would ve: oldValue1, NewValue1, oldValue2, NewValue2....oldValue6, NewValue6.



This solution does not seem to me as a best practice, I mean we can t alter the Rate object and design it to fit and accomodate the look of the UI, it should be the other way around, right ?

Anyway, here is what I did for now as a solution:

I create the column OldValue which is UNBOUND to the bindingsource. The column NewValue is BOUND to the binding source.

During the 1st load of the page: after databindingcomplete, I copy the value of the column NewValue into the unbound column OldValue, that s done only during the first load of the form, this way, subsequent changes of the column NewValue does not affect the readonly OldValue.



I hope this is good solution, let me know if u have other solutions

Thank u

[stanav]

So let's say when the form starts, the oldvalue = newvalue = 100 for example. The user changes the newvalue to 200. At this point, the oldvalue is still 100 and newvalue is 200. All is good. And then the user later changes his mind again and wants to make the newvalue = 300. Shouldn't the oldvalue now is 200 instead of staying fixed at 100 regardless of how many times newvalue gets changed?