Add dynamic Rows in GridView with TextBox and keep the edited GridViewRow Data on Post back in ASP.Net

I have 3 textboxes , 1 dropdown , 1 Button and 1 gridview .

Textboxes ID are : ACode , ADesc , ASeq

DropDown ID is : CPhase

Button ID is : AddRowBTN

GridView ID is : PhasesTempGrid

Now whats the story is ? After adding some data into textboxes , when a user clicks ADDRow BTN , that data gets saved into datatable , then that datatable gets binded to gridview and it shows my textboxes data in it .

What i want to achieve ? In my gridview i am use templateField and inside that template field there are textboxes ( Let the users edit the row without clicking any button ) .

Take an example of dummy data and problem persisting in there : for e.g i put some data in textboxes : ACode = "ABCD" ADesc = "EFGH" ASeq = "HIJK" Then i click Add BTN , it saves the data in datatable and show in gridview , now if i do this in gridview : ACode = "Edited ABCD" ADesc = "Edited EFGH too" ASeq = "WoW There" Then i click Add BTN , it removes the edited record in gridview and shows original data which had came earlier from textboxes : ACode = "ABCD" ADesc = "EFGH" ASeq = "HIJK" I don't want that to be done ... Simple is that user can enter data from textboxes , click the btn to submit into grid then he can edit the data like he want ... data must not get flashed , here's my coding i have done so far :  

 public void AddNewData()
    {
        var dt = new DataTable();
        if (ViewState["myDatatable"] != null)
        {
            dt = (DataTable) ViewState["myDatatable"];
        }
        else
        {
            dt.Columns.Add("CPhase");
            dt.Columns.Add("ACode");
            dt.Columns.Add("ADesc");
            dt.Columns.Add("ASeq");
        }

        DataRow drow = dt.NewRow();
        drow["CPhase"] = PhasesDrpDown.SelectedItem.Text;
        drow["ACode"] = ACode.Text;
        drow["ADesc"] = ADesc.Text.Trim();
        drow["ASeq"] = ActSeq.Value.Trim();
        dt.Rows.Add(drow);
        ViewState["myDatatable"] = dt;
        ACode.Text = string.Empty;
        ADesc.Text = string.Empty;
        ActSeq.Value = string.Empty;
    }

    public void BindMyGridview()
    {
        if (ViewState["myDatatable"] != null)
        {
            var dt = (DataTable) ViewState["myDatatable"];

            if ((dt != null) && (dt.Rows.Count > 0))
            {
                var dv = new DataView();
                dv = dt.DefaultView;
                dv.Sort = "CPhase,ASeq,ACode";
                PhasesTempGrid.DataSource = dt;
                PhasesTempGrid.DataBind();
                SearchPanel.Visible = true;
                int tb = dt.Rows.Count;
                TotalRows.Text = tb + " Activites";
            }
        }
    }
 

  protected void AddRowBTN_OnServerClick(object sender, EventArgs e)
    {
        AddNewData();
        BindMyGridview();
   }

and in code-behind code is :

 <asp:gridview ID="PhasesTempGrid" ClientIDMode="Static"   allowpaging="True" 
                                                                  OnPageIndexChanging="PhasesTempGrid_OnPageIndexChanging"   PageSize = "5"  PagerStyle-CssClass="custompaging" AllowSorting="True"
                                                                  runat="server" AutoGenerateColumns="False" CssClass="table table-bordered" BackColor="White" ForeColor="Black" BorderStyle="Groove" 
                                                                  ShowFooter="True">
                                                        <Columns>
                                                            <asp:TemplateField HeaderText="Activity Code">
                                                                <ItemTemplate>
                                                                    <asp:Label ID="ACodeLabel" runat="server" Text='<%#Eval("ACode") %>'></asp:Label>
                                                                </ItemTemplate>
                                                            </asp:TemplateField>
                                                            <asp:TemplateField HeaderText="Activity Sequence">
                                                                <ItemTemplate>
                                                                    <asp:Label ID="ASeqLabel" runat="server" Text='<%#Eval("ASeq") %>'></asp:Label>
                                                                </ItemTemplate>
                                                            </asp:TemplateField>
                                                            <asp:TemplateField HeaderText="Construction Phase">
                                                                <ItemTemplate>
                                                                    <asp:Label ID="CPhaseTempLabel" runat="server" Text='<%#Eval("CPhase") %>'></asp:Label>
                                                                </ItemTemplate>
                                                            </asp:TemplateField>
                                                            <asp:TemplateField HeaderText="Activity Description / Name">
                                                                <ItemTemplate>
                                                                    <asp:TextBox ID="ADescLabel" runat="server" Text='<%#Eval("ADesc") %>'></asp:TextBox>
                                                                </ItemTemplate>
                                                            </asp:TemplateField>

                                                            <asp:TemplateField>
                                                                <ItemTemplate>
                                                                    <asp:LinkButton ID="RemoveRow" CssClass="btn btn-danger btn-block" OnClick="RemoveRow_OnClick" runat="server" >Remove</asp:LinkButton>
                                                                </ItemTemplate>
                                                            </asp:TemplateField>
                                                        </Columns>
                                                        <FooterStyle CssClass="panel-heading" />
                                                        <PagerStyle BackColor="PaleGoldenrod" ForeColor="DarkSlateBlue" HorizontalAlign="Center" />
                                                        <HeaderStyle  CssClass="customGridViewHeader"  ForeColor="black"/>  
                                                    </asp:gridview>

here i havent added dropdown combo in gridview but you can do it so that it will save my time (Bind it just the way PhaseDropDown have bind)...