> Hi!
>
> Scenario: A User deletes a row in a DataTable; a MessageBox comes up and
> asks if he/she really wants to delete the row; in case the answer is "no",
> the row deletion should be cancelled.
>
> There are straightforward solutions for this scenario when an intelligent
> control like the DataGridView is used, because such control exhibits a
> "UserDeletingRow" event that provides a CANCEL property to be set to TRUE.
>
> But in case no such control is used, I cannot see a clear solution. I have
> searched the newsgroups for this, and I find two proposals:
>
> 1) Use the RowDeleted event of the DataRow by calling
> DataRow.RejectChanges(). I admit this to be a feasible solution, but it
> has
> nasty side effects, like:
>
> - the row will first be deleted and only then be "un-deleted" - including
> possible child rows (possibly several generations of them), that also have
> to
> be un-deleted
>
> - after the delete, a lot of other actions occur, like position changes,
> for example, that also have to be undone
>
> I conclude that using RowDeleted is not a good a solution (and I guess
> that
> the architects of the DataGridView would agree, because they provided
> something better).
>
> 2) Use the RowDeleting event of the DataRow.
>
> This looks better, because the RowDeleting event is called before the row
> is
> actually deleted. But - helas - this event doesn't have a CANCEL property.
>
> In the newsgroups I found a solution based on this idea by David Sceppa
> (whom I truely admire), which goes like this (I cite):
>
> *******David Sceppa speaking******
>
>     You could trap for the RowDeleting event and call the
> DataRow's RejectChanges method if you do not want to allow the
> deletion.  You could also throw an exception if that's
> appropriate in your application.
>
>
>     Here's some sample code I used to accomplish this task:
>
>
>  DataTable tbl = new DataTable();
>  tbl.Columns.Add("CustomerID");
>  tbl.Columns.Add("CompanyName");
>  tbl.LoadDataRow(new object[] {"Comp1", "Company #1"}, true);
>
>
>  tbl.RowDeleting += new DataRowChangeEventHandler(DeleteHandler);
>  Console.WriteLine(tbl.Rows.Count);
>  try
>  {
>    tbl.Rows[0].Delete();
>  }
>  catch (Exception ex)
>  {
>    Console.WriteLine(ex.Message);
>  }
>  Console.WriteLine(tbl.Rows.Count);
>
>
>  static void DeleteHandler(object sender, DataRowChangeEventArgs
> e)
>  {
>    e.Row.RejectChanges();
>    throw new Exception("Deletion disallowed");
>  }
>
>
>     I hope this information proves helpful.
>
> *******End of Citation *******
>
> The point here seems to be to throw the exception. As far as I can see,
> RejectChanges() doesn't do anything, because at this point in time, the
> row
> to be deleted still has a RowState of "Unchanged" (this is what my
> debugger
> tells me), and you cannot reject a change that has not yet taken place.
>
> In David's example, to throw an exception does the job, because the row is
> deleted *programmatically*, and hence, there is a point where the
> exception
> thrown can be caught. But what can I do when the row is deleted by a user
> action, like, pressing the Delete button on a BindingNavigator? I have no
> idea where I could catch the exception thrown.
>
> Does anybody have an idea? Thanks for any hints.
>
> Axel Hecker
>

"Patrice" wrote:

> You could ask confirmation in your UI code before performing the actual
> deletion ? What is the control that triggers this ? A button ?
>
> --
> Patrice
>
> "AxelHecker" <AxelHec***@discussions.microsoft.com> a écrit dans le message
> de news: 15162EEC-4C2B-419E-A6C5-D3E4ED453***@microsoft.com...
> > Hi!
> >
> > Scenario: A User deletes a row in a DataTable; a MessageBox comes up and
> > asks if he/she really wants to delete the row; in case the answer is "no",
> > the row deletion should be cancelled.
> >
> > There are straightforward solutions for this scenario when an intelligent
> > control like the DataGridView is used, because such control exhibits a
> > "UserDeletingRow" event that provides a CANCEL property to be set to TRUE.
> >
> > But in case no such control is used, I cannot see a clear solution. I have
> > searched the newsgroups for this, and I find two proposals:
> >
> > 1) Use the RowDeleted event of the DataRow by calling
> > DataRow.RejectChanges(). I admit this to be a feasible solution, but it
> > has
> > nasty side effects, like:
> >
> > - the row will first be deleted and only then be "un-deleted" - including
> > possible child rows (possibly several generations of them), that also have
> > to
> > be un-deleted
> >
> > - after the delete, a lot of other actions occur, like position changes,
> > for example, that also have to be undone
> >
> > I conclude that using RowDeleted is not a good a solution (and I guess
> > that
> > the architects of the DataGridView would agree, because they provided
> > something better).
> >
> > 2) Use the RowDeleting event of the DataRow.
> >
> > This looks better, because the RowDeleting event is called before the row
> > is
> > actually deleted. But - helas - this event doesn't have a CANCEL property.
> >
> > In the newsgroups I found a solution based on this idea by David Sceppa
> > (whom I truely admire), which goes like this (I cite):
> >
> > *******David Sceppa speaking******
> >
> >     You could trap for the RowDeleting event and call the
> > DataRow's RejectChanges method if you do not want to allow the
> > deletion.  You could also throw an exception if that's
> > appropriate in your application.
> >
> >
> >     Here's some sample code I used to accomplish this task:
> >
> >
> >  DataTable tbl = new DataTable();
> >  tbl.Columns.Add("CustomerID");
> >  tbl.Columns.Add("CompanyName");
> >  tbl.LoadDataRow(new object[] {"Comp1", "Company #1"}, true);
> >
> >
> >  tbl.RowDeleting += new DataRowChangeEventHandler(DeleteHandler);
> >  Console.WriteLine(tbl.Rows.Count);
> >  try
> >  {
> >    tbl.Rows[0].Delete();
> >  }
> >  catch (Exception ex)
> >  {
> >    Console.WriteLine(ex.Message);
> >  }
> >  Console.WriteLine(tbl.Rows.Count);
> >
> >
> >  static void DeleteHandler(object sender, DataRowChangeEventArgs
> > e)
> >  {
> >    e.Row.RejectChanges();
> >    throw new Exception("Deletion disallowed");
> >  }
> >
> >
> >     I hope this information proves helpful.
> >
> > *******End of Citation *******
> >
> > The point here seems to be to throw the exception. As far as I can see,
> > RejectChanges() doesn't do anything, because at this point in time, the
> > row
> > to be deleted still has a RowState of "Unchanged" (this is what my
> > debugger
> > tells me), and you cannot reject a change that has not yet taken place.
> >
> > In David's example, to throw an exception does the job, because the row is
> > deleted *programmatically*, and hence, there is a point where the
> > exception
> > thrown can be caught. But what can I do when the row is deleted by a user
> > action, like, pressing the Delete button on a BindingNavigator? I have no
> > idea where I could catch the exception thrown.
> >
> > Does anybody have an idea? Thanks for any hints.
> >
> > Axel Hecker
> >
>
>
>

"AxelHecker" wrote:

> Hi Patrice. As I said in my example, the control that triggers this is the
> "Delete"-button in a BindingNavigator. Actually, this button does have a
> Click event, but unfortunately, this event only fires when the RowDelete has
> already completed (both RowDeleting and RowDeleted events of the DataRow come
> before the Click event of the Delete-button of the BindingNavigator).
> Consequently, to do anything in the Click event of the Delete-button is of no
> use.
>
> Thanks for your comment anyway. Axel.
>
>
> --
> Axel Hecker
>
>
>
> "Patrice" wrote:
>
> > You could ask confirmation in your UI code before performing the actual
> > deletion ? What is the control that triggers this ? A button ?
> >
> > --
> > Patrice
> >
> > "AxelHecker" <AxelHec***@discussions.microsoft.com> a écrit dans le message
> > de news: 15162EEC-4C2B-419E-A6C5-D3E4ED453***@microsoft.com...
> > > Hi!
> > >
> > > Scenario: A User deletes a row in a DataTable; a MessageBox comes up and
> > > asks if he/she really wants to delete the row; in case the answer is "no",
> > > the row deletion should be cancelled.
> > >
> > > There are straightforward solutions for this scenario when an intelligent
> > > control like the DataGridView is used, because such control exhibits a
> > > "UserDeletingRow" event that provides a CANCEL property to be set to TRUE.
> > >
> > > But in case no such control is used, I cannot see a clear solution. I have
> > > searched the newsgroups for this, and I find two proposals:
> > >
> > > 1) Use the RowDeleted event of the DataRow by calling
> > > DataRow.RejectChanges(). I admit this to be a feasible solution, but it
> > > has
> > > nasty side effects, like:
> > >
> > > - the row will first be deleted and only then be "un-deleted" - including
> > > possible child rows (possibly several generations of them), that also have
> > > to
> > > be un-deleted
> > >
> > > - after the delete, a lot of other actions occur, like position changes,
> > > for example, that also have to be undone
> > >
> > > I conclude that using RowDeleted is not a good a solution (and I guess
> > > that
> > > the architects of the DataGridView would agree, because they provided
> > > something better).
> > >
> > > 2) Use the RowDeleting event of the DataRow.
> > >
> > > This looks better, because the RowDeleting event is called before the row
> > > is
> > > actually deleted. But - helas - this event doesn't have a CANCEL property.
> > >
> > > In the newsgroups I found a solution based on this idea by David Sceppa
> > > (whom I truely admire), which goes like this (I cite):
> > >
> > > *******David Sceppa speaking******
> > >
> > >     You could trap for the RowDeleting event and call the
> > > DataRow's RejectChanges method if you do not want to allow the
> > > deletion.  You could also throw an exception if that's
> > > appropriate in your application.
> > >
> > >
> > >     Here's some sample code I used to accomplish this task:
> > >
> > >
> > >  DataTable tbl = new DataTable();
> > >  tbl.Columns.Add("CustomerID");
> > >  tbl.Columns.Add("CompanyName");
> > >  tbl.LoadDataRow(new object[] {"Comp1", "Company #1"}, true);
> > >
> > >
> > >  tbl.RowDeleting += new DataRowChangeEventHandler(DeleteHandler);
> > >  Console.WriteLine(tbl.Rows.Count);
> > >  try
> > >  {
> > >    tbl.Rows[0].Delete();
> > >  }
> > >  catch (Exception ex)
> > >  {
> > >    Console.WriteLine(ex.Message);
> > >  }
> > >  Console.WriteLine(tbl.Rows.Count);
> > >
> > >
> > >  static void DeleteHandler(object sender, DataRowChangeEventArgs
> > > e)
> > >  {
> > >    e.Row.RejectChanges();
> > >    throw new Exception("Deletion disallowed");
> > >  }
> > >
> > >
> > >     I hope this information proves helpful.
> > >
> > > *******End of Citation *******
> > >
> > > The point here seems to be to throw the exception. As far as I can see,
> > > RejectChanges() doesn't do anything, because at this point in time, the
> > > row
> > > to be deleted still has a RowState of "Unchanged" (this is what my
> > > debugger
> > > tells me), and you cannot reject a change that has not yet taken place.
> > >
> > > In David's example, to throw an exception does the job, because the row is
> > > deleted *programmatically*, and hence, there is a point where the
> > > exception
> > > thrown can be caught. But what can I do when the row is deleted by a user
> > > action, like, pressing the Delete button on a BindingNavigator? I have no
> > > idea where I could catch the exception thrown.
> > >
> > > Does anybody have an idea? Thanks for any hints.
> > >
> > > Axel Hecker
> > >
> >
> >
> >