dropdownlist does not retain values after communicating with masterpage

i have a filter option in a table


so the filter works


but when i click the edit icon on the right then it hits the master page and does a postback and reloads the dropdownlist vales again that resets it back to selected index = 0, how can i avoid this postback to retain the filter values?

so this is how i initally populate the dropdown list on page_load

 if (amiadmin == "YES" || amiadmin == "NO")
                    {
                        if (!IsPostBack)
                        {
                            headervaluess.Items.Clear();
                            for (int i = 0; i < GridView1s.Columns.Count; i++)
                            {
                                if (GridView1s.Columns[i].HeaderText != "MultipleApproval" && GridView1s.Columns[i].HeaderText != "" && GridView1s.Columns[i].HeaderText != "Date" && GridView1s.Columns[i].HeaderText != "TimeStamp" && GridView1s.Columns[i].HeaderText != "Explanation_Details")
                                {
                                    if (GridView1s.Columns[i].HeaderText == "Item Code")
                                    {
                                        headervaluess.Items.Add(GridView1s.Columns[i].HeaderText.Replace("Item Code", "Item_Code"));
                                    }
                                    else if (GridView1s.Columns[i].HeaderText == "Item Description")
                                    {
                                        headervaluess.Items.Add(GridView1s.Columns[i].HeaderText.Replace("Item Description", "Item_Desc"));
                                    }
                                    else if (GridView1s.Columns[i].HeaderText == "FirstQual")
                                    {
                                        headervaluess.Items.Add(GridView1s.Columns[i].HeaderText.Replace("FirstQual", "[1st_Quality]"));
                                    }
                                    else if (GridView1s.Columns[i].HeaderText == "uncoated")
                                    {
                                        headervaluess.Items.Add(GridView1s.Columns[i].HeaderText.Replace("uncoated", "Un_coated_rework"));
                                    }
                                    else if (GridView1s.Columns[i].HeaderText == "coatedrework")
                                    {
                                        headervaluess.Items.Add(GridView1s.Columns[i].HeaderText.Replace("coatedrework", "CoatedRework"));
                                    }
                                    else if (GridView1s.Columns[i].HeaderText == "purgeout")
                                    {
                                        headervaluess.Items.Add(GridView1s.Columns[i].HeaderText.Replace("purgeout", "Purge_Out_UC_Rework"));
                                    }
                                    else if (GridView1s.Columns[i].HeaderText == "FloorWaste")
                                    {
                                        headervaluess.Items.Add(GridView1s.Columns[i].HeaderText.Replace("FloorWaste", "Floor_Waste"));
                                    }
                                    else if (GridView1s.Columns[i].HeaderText == "MachineWaste")
                                    {
                                        headervaluess.Items.Add(GridView1s.Columns[i].HeaderText.Replace("MachineWaste", "Machine_Waste"));
                                    }
                                    else if (GridView1s.Columns[i].HeaderText == "purgeouts")
                                    {
                                        headervaluess.Items.Add(GridView1s.Columns[i].HeaderText.Replace("purgeouts", "Purge_Out"));
                                    }
                                    else if (GridView1s.Columns[i].HeaderText == "rsw")
                                    {
                                        headervaluess.Items.Add(GridView1s.Columns[i].HeaderText.Replace("rsw", "Roller_Scraper_Waste"));
                                    }
                                    else if (GridView1s.Columns[i].HeaderText == "EW")
                                    {
                                        headervaluess.Items.Add(GridView1s.Columns[i].HeaderText.Replace("EW", "Extraordinary_Waste"));
                                    }
                                    else if (GridView1s.Columns[i].HeaderText == "NoFCR")
                                    {
                                        headervaluess.Items.Add(GridView1s.Columns[i].HeaderText.Replace("NoFCR", "NOFCR"));
                                    }
                                    else if (GridView1s.Columns[i].HeaderText == "ActualWasteShipments")
                                    {
                                        headervaluess.Items.Add(GridView1s.Columns[i].HeaderText.Replace("ActualWasteShipments", "[Actual_Waste_Shipment]"));
                                    }
                                    else
                                    {
                                        headervaluess.Items.Add(GridView1s.Columns[i].HeaderText);
                                    }
                                }
                                else
                                {

                                }

                            }
                        }//AvailableLinesQuery = "SELECT TOP (100) PERCENT Line FROM dbo.General WITH (nolock) WHERE  ((VStatus < 2) AND (plant = @Plant) and  (DateEntered >= @DDate) and (WhichMenuItem = @WhichMenuItem)) OR   ((VStatus = 0) AND (Plant = @Plant) AND (WhichMenuItem = @WhichMenuItem)) GROUP BY Line";
                        //AvailableMachinesQuery = "SELECT TOP (100) PERCENT Machine FROM dbo.General WITH (nolock) WHERE  ((VStatus < 2) AND (plant = @Plant) and  (DateEntered >= @DDate) and (WhichMenuItem = @WhichMenuItem)) OR   ((VStatus = 0) AND (Plant = @Plant) AND (WhichMenuItem = @WhichMenuItem)) GROUP BY Machine";
                       // headervaluess.Items.Insert(0, new ListItem(String.Empty, String.Empty));
                        //headervaluess.SelectedIndex = 0;
                    }

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the above code should only run initially when its not postback because i want the drop down list to retain the values but what happens is  the content page goes to Master page and when it returns back to content page again it runs the page load as non postback runs populating the drop downlist values. <- this happens when i click on the edit button.

any help is appreciated.

Thanks