Question

I have a datagrid in VB.NET class. The cells are editable. Is there any way to trigger a function when each of the cells are edited?

Answer 1

Yes, the CellValueChanged Event:
http://msdn.microsoft.com/en-us/library/system.windows.forms.datagridview.cellvaluechanged.aspx

    Private Sub DataGridView1_CellValueChanged(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles DataGridView1.CellValueChanged
       'do something
    End Sub

EDIt as per your comment:
Yes you could save the current value to a class level variable on BeginEdit and retreieve it in the CellValueChanged event:

Private cellValue As String = String.Empty

Private Sub DataGridView1_CellBeginEdit(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewCellCancelEventArgs) Handles DataGridView1.CellBeginEdit
    cellValue = DataGridView1.Rows(e.RowIndex).Cells(e.ColumnIndex).Value.ToString
End Sub

Private Sub DataGridView1_CellValueChanged(ByVal sender As Object, ByVal e As System.Windows.Forms.DataGridViewCellEventArgs) Handles DataGridView1.CellValueChanged
    MessageBox.Show("row index: " & e.RowIndex & Environment.NewLine & "old value: " & cellValue)
End Sub