c# asp.net wie kann ich die Bild-url " - Taste (es-Typ-Bild ) wenn ich auf die Schaltfläche in der gridview

Erstellte ich eine gridview es hat Favoriten-button und ich möchte die url ändern, wenn ich drauf klicke. wie kann ich es tun?

  <asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" 
            DataSourceID="SqlDataSource1" Width="446px" AllowPaging="True" 
            onrowcommand="GridView1_RowCommand1" 
            onselectedindexchanged="GridView1_SelectedIndexChanged">
                <Columns>
                    <asp:ImageField AlternateText="Add To Favorites" Visible=false 
                        DataImageUrlFormatString="&quot;~/images/favorites.png&quot;" 
                        FooterText="Add To Favorites" HeaderText="Add To Favorites">
                        <FooterStyle Width="10px" />
                    </asp:ImageField>
                    <asp:ButtonField CommandName="AddComment" ButtonType="Image" HeaderText="Comment" ImageUrl="~/images/commentt.png" Text="Comment" ItemStyle-HorizontalAlign="Center" >
                     <ItemStyle HorizontalAlign="Center"></ItemStyle>
                    </asp:ButtonField>
                    <asp:ButtonField CommandName="Share"  ButtonType="Image" HeaderText="Share with Friends" ImageUrl="~/images/openshare.png" ItemStyle-HorizontalAlign="Center" Text="Share" >
                    <ItemStyle HorizontalAlign="Center"></ItemStyle>
                    </asp:ButtonField>
                     <asp:ButtonField CommandName="ShareGroups"  ButtonType="Image" HeaderText="Share with Groups"   ImageUrl="~/images/openshare.png" ItemStyle-HorizontalAlign="Center" Text="Share" >
                    <ItemStyle HorizontalAlign="Center"></ItemStyle>
                    </asp:ButtonField>
                  <asp:ButtonField ButtonType="Image" HeaderText="Favorites" 
                        ImageUrl="~/images/StarEmpty.png" CommandName="Favorite" 
                        Text="Add to Favorites" ItemStyle-HorizontalAlign="Center">
                    <FooterStyle Height="20px" />
                    <HeaderStyle Width="3px" />
                    <ItemStyle HorizontalAlign="Center"></ItemStyle>
                    </asp:ButtonField>
                    <asp:ButtonField  ButtonType="Image"  CommandName="Mail" HeaderText="Send Mail" 
                        ImageUrl="~/images/email-icon.png.jpg" Text="Send Mail" 
                        ItemStyle-HorizontalAlign="Center" InsertVisible="False" >

                            <ItemStyle HorizontalAlign="Center"></ItemStyle>

                    </asp:ButtonField>
                    <asp:ButtonField CommandName="View" Text="View Rss" 
                        HeaderText="View Rss" ItemStyle-HorizontalAlign="Center" >
                    <HeaderStyle Width="50px" />
                    <ItemStyle Width="15px" />

                    </asp:ButtonField>
                     <asp:BoundField DataField="RSS_Title" HeaderText="RSS_Title"
                        SortExpression="RSS_Title" />
                   <asp:TemplateField>
            <ItemTemplate>
                <asp:HiddenField ID="HiddenField1" runat="server" 
                    Value='<%#Eval("RSS_ID")%>'/>

            </ItemTemplate>

            </asp:TemplateField>
                </Columns>
            </asp:GridView>

Mein c# - codes sind unten

  if (e.CommandName == "Favorite")
        {
           //GridView1.Rows[rowIndex].Cells[2].

            string sValue = ((HiddenField)GridView1.Rows[rowIndex].FindControl("HiddenField1")).Value;
            int id = Convert.ToInt32(sValue);
            Session["SelectedRSS"] = sValue;

            DBConnection db = new DBConnection();
            bool res = db.CheckFavorites(id, User_Name);

            //if favorite rss  doesnot exist
            if (!res)
            {
                Boolean result = db.addFavorite(id, User_Name);

        DataSet selectedRSS = db.getRSS(id);
        DataTable dt = selectedRSS.Tables[0];
        DataRow row = null;

        for (int i = 0; i < dt.Rows.Count; i++)
        {
            row = dt.Rows[i];
            countOfFavorite = Convert.ToInt32(row[3].ToString());

        }
        countOfFavorite++;

                Boolean result1 = db.increaseFavoriteCount(id, countOfFavorite);

                //rssi favori olarak user dosyasına kaydet;


            }


        }