DataTable Events Working in VB.NET

In this article I will explain working with DataTable Events in ADO.NET.
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A DataTable represents a table of a dataset. DataTable provides many events that an application can track down (see Table 9-5).
 
Table 9-5. The DataTable Events
 

EVENT

DESCRIPTION

ColumnChanged

This event occurs when a value of a column has been changed.

ColumnChanging

This event occurs when a new value is being added to a column.

RowChanged

This event occurs when a value of a row in the table has been changed.

RowChanging

This event occurs when a row in a table has been changed.

RowDeleted

This event occurs when a row in a table has been deleted.

RowDeleting

This event occurs when a row is being deleted.


ColumnChangedEventHandler handles the ColumnChanged event; it's as follows:

Public Delegate Sub DataColumnChangeEventHandler(ByVal senderAs Object,ByVal e As DataColumnChangeEventArgs)Public Delegate Sub DataColumnChangeEventHandler(ByVal senderAs Object,ByVal e As DataColumnChangeEventArgs)
 
Where sender is the source of the event and e is DataColumnChangedEventArgs, which contains the event data.
 
ColumnChangingEventHandler handles the ColumnChanging Event; it's as follows:

Public delegate void DataColumnChangeEventHandler(Object sender,DataColumnChangeEventArgs e)

 
Where Sender is the source of the event and e is DataColumnChangingEventArgs, which contains the event data.

 
Similarly, to these two handlers, RowChangedEventHandler, RowChangingEventHandler, RowDeletingEventHandler, and RowDeletedEventHandler handle the RowChanged, RowChanging, RowDeleting, and RowDeleted events, respectively. Definitions of these event handlers are similar to DataColumnChangingEventHandler and DataColumnChangedEventHandler.
 
To test these I'll create a data table, add data rows to the table, and then update and delete rows from the table.
 
Listing 9-8 creates a data table, adds three columns (id, name, and address), adds data to the table, and changes the columns of the table. It also calls the ColumnChanged and ColumnChanging event handlers. You write the code for the ColumnChanged and ColumnChanging event handlers in the Column_Changed and Column_Changing methods. Specifically, you can write this code on a button-click event handler.
 
Listing 9-8. Writing the Column and ColumnChanged event handlers

    Private Sub ColumnChange_Click(ByVal sender As Object,ByVal e As System.EventArgs)
        Dim custTableAs New DataTable("Customers")

        ' add columns
        custTable.Columns.Add("id",GetType(Integer))
        custTable.Columns.Add("name",GetType(String))
        custTable.Columns.Add("address",GetType(String))

        ' Add ColumnChanging and ColumnChanged event handlers
        AddHandler custTable.ColumnChanging, AddressOf Column_Changing
        AddHandler custTable.ColumnChanged,AddressOf Column_Changed

        ' add Two rows
        custTable.Rows.Add(New Object() {1, "name1", "address1"})
        custTable.Rows.Add(New Object() {2, "name2", "address2"})
        custTable.AcceptChanges()

        ' Change the name column in all the rows
        For Each row As DataRowIn custTable.Rows
            row("name") ="new name"
        Next
    End Sub

    Private Shared Sub Column_Changed(ByVal senderAs Object,ByVal e As DataColumnChangeEventArgs)
        MessageBox.Show(((("Column_changed Event: " & " , ") + e.Row("name") & " ,") + e.Column.ColumnName &", ") + e.Row("name", DataRowVersion.Original))
    End Sub

    Private Shared Sub Column_Changing(ByVal senderAs Object,ByVal e As DataColumnChangeEventArgs)
        MessageBox.Show(((("Column_changing Event: " & " , ") + e.Row("name") & " ,") + e.Column.ColumnName &", ") + e.Row("name", DataRowVersion.Original))
    End Sub
 

Listing 9-9 creates a data table, adds three columns (id, name, and address), adds data to the table, and changes the columns of the table. It also calls the RowChanging and RowChanged event handlers.
 
Listing 9-9. Writing the RowChanging and RowChanged event handlers

    Private Sub UpdateRow_Click(ByVal sender As Object,ByVal e As System.EventArgs)
        Dim custTableAs New DataTable("Customers")

        ' add columns
        custTable.Columns.Add()
        custTable.Columns.Add("id",GetType(Integer))
        custTable.Columns.Add("name",GetType(String))
        custTable.Columns.Add("address",GetType(String))

        ' add Two rows
        custTable.Rows.Add(New Object() {1, "name1", "address1"})
        custTable.Rows.Add(New Object() {2, "name2", "address2"})
        custTable.AcceptChanges()

        For Each row As DataRow In custTable.Rows
            row("name") ="new name"

            ' Adding RowChanged and RowChanging event handlers
            AddHandler custTable.RowChanged, AddressOf Row_Changed
            AddHandler custTable.RowChanging,AddressOf Row_Changing
        Next
    End Sub

    Private Shared Sub Row_Changed(ByVal senderAs Object,ByVal e As DataRowChangeEventArgs)
        MessageBox.Show(("Row_Changed Event:" & e.Row("name", DataRowVersion.Original).ToString()) + e.Action.ToString())
    End Sub

    Private Shared Sub Row_Changing(ByVal senderAs Object,ByVal e As DataRowChangeEventArgs)
        MessageBox.Show(("Row_Changing Event:" & e.Row("name", DataRowVersion.Original).ToString()) + e.Action.ToString())
    End Sub

 

Listing 9-10 creates a data table, adds three columns (id, name, and address), adds data to the table, and changes the columns of the table. It also calls the RowDeleting and RowDeleted event handlers.
 
Listing 9-10. Writing the RowDeleting and RowDeleted event handlers

    Private Sub DeleteRow_Click(ByVal sender As Object,ByVal e As System.EventArgs)
        Dim custTableAs New DataTable("Customers")

        ' add columns
        custTable.Columns.Add()
        custTable.Columns.Add("id",GetType(Integer))
        custTable.Columns.Add("name",GetType(String))
        custTable.Columns.Add("address",GetType(String))

        ' Add RowDeleting and RowDeleted events
        AddHandler custTable.RowDeleting, AddressOf Row_Deleting
        AddHandler custTable.RowDeleted,AddressOf Row_Deleted

        ' add Two rows
        custTable.Rows.Add(New Object() {1, "name1", "address1"})
        custTable.Rows.Add(New Object() {2, "name2", "address2"})
        custTable.AcceptChanges()

        'Delete all the rows
        For Each row As DataRowIn custTable.Rows
            row.Delete()
        Next
    End Sub

    Private Shared Sub Row_Deleting(ByVal senderAs Object,ByVal e As DataRowChangeEventArgs)
        MessageBox.Show(("Row_ Deleting Event:" & e.Row("name", DataRowVersion.Original).ToString()) + e.Action.ToString())
    End Sub

    Private Shared Sub Row_Deleted(ByVal senderAs Object,ByVal e As DataRowChangeEventArgs)
        MessageBox.Show(("Row_Deleted Event:" & e.Row("name", DataRowVersion.Original).ToString()) + e.Action.ToString())
   End Sub
 

Conclusion
 
Hope this article would have helped you in understanding working with DataTable Events in ADO.NET. See other articles on the website also for further reference.

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