Unable to update in first click of button in gridview

Question

I have a gridview control . I Have a Added edit, delete, update, insert button. but update button works only when i double click on it . and also i am unable to change the page index when i click on index number of gridview.
here is the code for gridview

<asp:GridView ID="gvDetails" runat="server" DataKeyNames="CategoryID,Name" AutoGenerateColumns="false"         AllowPaging="true" AllowSorting="true" HeaderStyle-BackColor="#61A6F8" HeaderStyle-ForeColor="White"         ShowFooter="true" Height="282px" OnRowCancelingEdit="gvDetails_RowCancelingEdit"         OnRowCommand="gvDetails_RowCommand" OnRowDeleting="gvDetails_RowDeleting" OnRowEditing="gvDetails_RowEditing"         OnRowUpdating="gvDetails_RowUpdating" Width="600px" PageSize="5" ForeColor="White"         OnPageIndexChanging="gvDetails_PageIndexChanging">         <Columns>             <asp:TemplateField>                 <EditItemTemplate>                     <asp:ImageButton ID="imgbtnUpdate" CommandName="Update" runat="server" ImageUrl="~/Images/update.jpg"                         ToolTip="Update" Height="20px" Width="20px" />                     <asp:ImageButton ID="imgbtnCancel" runat="server" CommandName="Cancel" ImageUrl="~/Images/Cancel.jpg"                         ToolTip="Cancel" Height="20px" Width="20px" />                 </EditItemTemplate>                 <ItemTemplate>                     <asp:ImageButton ID="imgbtnEdit" CommandName="Edit" runat="server" ImageUrl="~/Images/Edit.jpg"                         ToolTip="Edit" Height="20px" Width="20px" />                     <asp:ImageButton ID="imgbtnDelete" CommandName="Delete" runat="server" ImageUrl="~/Images/delete.jpg"                         ToolTip="Delete" Height="20px" Width="20px" />                 </ItemTemplate>                 <FooterTemplate>                     <asp:ImageButton ID="imgbtnAdd" runat="server" ImageUrl="~/Images/AddNewitem.jpg"                         CommandName="AddNew" Width="30px" Height="30px" ToolTip="Add new User" />                 </FooterTemplate>             </asp:TemplateField>             <asp:TemplateField HeaderText="CategoryID">                 <EditItemTemplate>                     <asp:TextBox ID="txtCatID" runat="server" Text='<%#Eval("CategoryID")%>'></asp:TextBox>                 </EditItemTemplate>                 <ItemTemplate>                     <asp:Label ID="lblCategoryID" runat="server" Text='<%#Eval("CategoryID") %>'></asp:Label>                 </ItemTemplate>                 <FooterTemplate>                     <asp:TextBox ID="txtfCategoryID" runat="server"></asp:TextBox>                 </FooterTemplate>             </asp:TemplateField>             <asp:TemplateField HeaderText="Name">                 <EditItemTemplate>                     <asp:TextBox ID="txtName" runat="server" Text='<%#Eval("Name")%>'></asp:TextBox>                 </EditItemTemplate>                 <ItemTemplate>                     <asp:Label ID="lblName" runat="server" Text='<%#Eval("Name") %>'></asp:Label>                 </ItemTemplate>                 <FooterTemplate>                     <asp:TextBox ID="txtfname" runat="server"></asp:TextBox>                 </FooterTemplate>             </asp:TemplateField>         </Columns>     </asp:GridView>     <asp:Label ID="Label1" runat="server" Font-Bold="true"></asp:Label>


this is the code for .aspx.cs file

public partial class AddItems : System.Web.UI.Page {     SqlConnection con;     SqlCommand ecmd, acmd, dcmd;     string str = ConfigurationManager.ConnectionStrings["connect"].ConnectionString;     LoginView lv;     protected void Page_Load(object sender, EventArgs e)     {         lv = (LoginView)Master.FindControl("HeadLoginView");         if (!lv.Page.User.Identity.IsAuthenticated)         {             Response.Redirect("~/Account/Login.aspx?ReturnUrl=~/AddItems.aspx");         }         else         {             string lname = lv.Page.User.Identity.Name;             if (!lname.Equals("amit"))             {                 Response.Redirect("Default.aspx");             }         }         if (!IsPostBack)         {             showDataItem();         }     }      protected void showDataItem()     {         con = new SqlConnection(str);         con.Open();         SqlCommand cmd = new SqlCommand("select * from Items", con);         SqlDataAdapter da = new SqlDataAdapter(cmd);         DataSet ds = new DataSet();         da.Fill(ds);         gvItems.DataSource = ds;         gvItems.DataBind();         con.Close();     }       protected void gvItems_RowCommand(object sender, GridViewCommandEventArgs e)     {         if (e.CommandName.Equals("AddNew"))         {             lblMsg.Text = "";             con = new SqlConnection(str);             con.Open();             int IcatID = Convert.ToInt32(((TextBox)gvItems.FooterRow.FindControl("txtfCategoryID")).Text);             string Iname = ((TextBox)gvItems.FooterRow.FindControl("txtfname")).Text;             FileUpload IImag = (FileUpload)gvItems.FooterRow.FindControl("fuAddImg");             if (IImag.HasFile)             {                 IImag.SaveAs(Server.MapPath("~/Images/Items/") + IImag.FileName);                 acmd = new SqlCommand("insert into Items(CategoryID,Name,ImageUrl) values (@a,@b,@g)", con);                 acmd.Parameters.AddWithValue("@a", IcatID);                 acmd.Parameters.AddWithValue("@b", Iname);                 acmd.Parameters.AddWithValue("@g", "~/Images/Items/" + IImag.FileName);                 acmd.ExecuteNonQuery();                 con.Close();             }             else             {                 lblMsg.Text = "Item category requires an Image";                 lblMsg.ForeColor = Color.Red;             }             showDataItem();         }       }     protected void gvItems_RowDeleting(object sender, GridViewDeleteEventArgs e)     {          int getItemID = Convert.ToInt32(gvItems.DataKeys[e.RowIndex].Values["ItemID"].ToString());         con = new SqlConnection(str);         con.Open();         dcmd = new SqlCommand("delete from Items where ItemID=@a", con);         dcmd.Parameters.AddWithValue("@a", getItemID);         int flag = dcmd.ExecuteNonQuery();         if (flag == 1)         {             lblMsg.Text = "Record Deleted Successfully";             lblMsg.ForeColor = Color.Green;         }         else         {             lblMsg.Text = "Deletion UnSuccessfull";             lblMsg.ForeColor = Color.Red;         }         con.Close();         showDataItem();     }     protected void gvItems_RowEditing(object sender, GridViewEditEventArgs e)     {         gvItems.EditIndex = e.NewEditIndex;     }     protected void gvItems_RowUpdating(object sender, GridViewUpdateEventArgs e)     {      }     protected void gvItems_RowCancelingEdit(object sender, GridViewCancelEditEventArgs e)     {         gvItems.EditIndex = -1;         showDataItem();     }     protected void gvItems_PageIndexChanging(object sender, GridViewPageEventArgs e)     {         gvItems.PageIndex = e.NewPageIndex;     } }