Using arrows to change the order in which things are displayed in a GridView in ASP.NET

Question

I am trying to use images representing arrows to allow the user to change the order in which items appear in a list in a grid view in ASP.NET.

I have a class which has a value named "position", the class is displayed inside the GridView and is ordered by position. In each of the rows of the gridview are an up and down arrow which i want to change the value of "position" for the object represent by the row of the gridview. Whats the easiest way to do this?

ASP -

<br /><strong>Previous Employment: </strong> <br />
                Pick one of your previous employers listed below to update/delete or <asp:HyperLink ID="PreviousEmploymentLink" runat="server" />.
                <asp:GridView runat="server" ID="EmploymentDataGrid" AutoGenerateColumns="false" OnRowDeleting="EmploymentDataGrid_onDeleting" 
                DataKeyNames="EmployerId" SkinID="FullWidthGrid" >
                <EmptyDataTemplate>
                <p>No Previous Employment added yet</p>
                </EmptyDataTemplate>
                    <Columns>
                            <asp:BoundField HeaderText="Dates" DataField="Dates" />
                            <asp:BoundField HeaderText="Employer's Name" DataField="EmployerName" />
                            <asp:BoundField HeaderText="Job Description" DataField="JobDescription" />
                            <asp:BoundField HeaderText="Job Title" DataField="JobTitle" />
                            <asp:HyperLinkField HeaderStyle-Width="30px" DataNavigateUrlFields="EmployerId"
                            HeaderText="Edit" Text="<img src='../../../Images/edit.gif' alt='Edit Employment' border='0'/>"
                            DataNavigateUrlFormatString="UpdatePreviousEmployment.aspx?PreviousEmploymentId={0}" />
                            <asp:TemplateField HeaderText="Delete" ItemStyle-HorizontalAlign="Center" HeaderStyle-Width="45px">
                                <ItemTemplate>
                                    <asp:ImageButton AlternateText="Delete User" ID="DeleteButton" runat="server" CommandName="Delete" ImageUrl="~/Images/delete.gif" />
                                </ItemTemplate>
                            </asp:TemplateField>
                            <asp:TemplateField HeaderText="Position" ItemStyle-HorizontalAlign="Center" HeaderStyle-Width="45px">
                                <ItemTemplate>
                                    <asp:ImageButton AlternateText="Move Up" ID="UpPositionButton" runat="server" CommandName="MoveEmploymentUp" OnClick="MoveEmploymentUp" ImageUrl="~/Images/arrow_up_green.gif" />
                                    <asp:ImageButton AlternateText="Move Down" ID="DownPositionButton" runat="server" CommandName="MoveEmploymentDown" ImageUrl="~/Images/arrow_down_green.gif" />
                                </ItemTemplate>
                            </asp:TemplateField>
                    </Columns>
                </asp:GridView>

Answer 1

I have a few small remarks:

Nitpicking: movingEmployment whould be movingEmployee

//the following assignement is not used.
Employer emp = (Employer)g.DataItem;    

//This object should not be constructed by default.
Employer otherEmployment = new Employer();  

eDao.SaveOrUpdate(movingEmployment); 
//eDao.CommitChanges(); 
//I did not commit because if something went wrong right now,
//then the data for one would be updated but the other not.
eDao.SaveOrUpdate(otherEmployment); 
eDao.CommitChanges(); 

The revised code (slightly tweaked for performance) could be.

protected void MoveEmploymentUp(object sender, ImageClickEventArgs e) 
{ 
   ICVDao cvdao = DaoFactory.GetCVDao();
   CV currentCv = cvdao.GetById(Int32.Parse(Request.Params["CVID"]), false); 

   //Can only work with at least two items in the list.
   if(currentCv.Employment.Count > 1)
   {
     #region Get to the selected Employee reference
     IEmployerDao eDao = DaoFactory.GetEmployerDao(); 
     ImageButton i = (ImageButton)sender; 
     GridViewRow g = (GridViewRow)i.Parent.Parent;          
     EmploymentDataGrid.SelectedIndex = g.RowIndex;          
     Employer selectedEmployee = eDao.GetById(int.ParseEmploymentDataGrid.SelectedDataKey.Value.ToString()), false);      
     #endregion 

     int selectedPosition = selectedEmployee.Position;
     if (selectedPosition != 1)          
     {          
       #region find employee to swap with
       Employer swapWithEmployee = null;
       //I assume currentCv.Employment is only an IEnumerable.
       //If it was an Collection we would not have to loop.
       foreach (Employer findSwapEmployee in currentCv.Employment)          
       {          
           if (findSwapEmployee.Position == selectedPosition- 1) 
           {         
               swapWithEmployee= findSwapEmployee;          
               break;
           }          
       }
       #endregion 

       #region perform and commit swap
       if(swapWithEmployee != null)
       {
         selectedEmployee.Position -= 1;          
         swapWithEmployee.Position = selectedPosition;          

         eDao.SaveOrUpdate(selectedEmployee);          
         eDao.SaveOrUpdate(swapWithEmployee);          
         eDao.CommitChanges();          
         EmploymentGridBind();          
      }          
      #endregion 
   }      
}   

Answer 2

protected void MoveEmploymentUp(object sender, ImageClickEventArgs e)
{
    ICVDao cvdao = DaoFactory.GetCVDao();        

    CV currentCv = cvdao.GetById(Int32.Parse(Request.Params["CVID"]), false);

    IEmployerDao eDao = DaoFactory.GetEmployerDao();


    ImageButton i = (ImageButton)sender;

    /*
     * if chap above
     * Swap numbers with chap above
     * if not
     * dont swap
     */

    GridViewRow g = (GridViewRow)i.Parent.Parent;

    Employer emp = (Employer)g.DataItem;

    EmploymentDataGrid.SelectedIndex = g.RowIndex;
    Employer movingEmployment = eDao.GetById(int.Parse(EmploymentDataGrid.SelectedDataKey.Value.ToString()), false);

    Employer otherEmployment = new Employer();

    if (movingEmployment.Position != 1 && currentCv.Employment.Count > 1)
    {
        foreach (Employer em in currentCv.Employment)
        {
            if (em.Position == movingEmployment.Position - 1)
                otherEmployment = em;
        }

        movingEmployment.Position -= 1;
        otherEmployment.Position += 1;

        eDao.SaveOrUpdate(movingEmployment);
        eDao.CommitChanges();
        eDao.SaveOrUpdate(otherEmployment);
        eDao.CommitChanges();

        EmploymentGridBind();

        //InstructionsLabel.Text = "Mover Dates:" +movingEmployment.Dates+ " ID:" + movingEmployment.EmployerId + " Position:" + movingEmployment.Position +
        //    "<br />Other Dates:" + otherEmployment.Dates + " ID:" + otherEmployment.EmployerId + " Position:" + otherEmployment.Position;
    }

}

Had to get the datakey value via the gridview object as opposed to the gridviewrow, using that, the rest was easy