The name does not exist in current context [error]

I have a custom cell with a stack layout [with a label and a image button] in a list view when im trying to change the isVisibility of image button iam getting this error.
<?xml version="1.0" encoding="UTF-8"?>

<MasterDetailPage.Master>

        <ContentPage.Content >

               <ListView x:Name="list_menuPage" >
                    <ListView.ItemTemplate>
                        <DataTemplate>                            
                           <ViewCell>
                                <StackLayout x:Name="ChildItems" Orientation="Horizontal">
                                    <Label Text="{Binding NAME}" TextColor="Navy" HorizontalOptions="StartAndExpand"/>
                                    <ImageButton Source="right_arrow.png" IsVisible="{Binding IsSelected}" x:Name="subListButton" HorizontalOptions="EndAndExpand" Margin="5,10" Clicked="Handle_Clicked"/>
                                </StackLayout>
                            </ViewCell>
                        </DataTemplate>
                    </ListView.ItemTemplate>
                  </ListView>

            </ContentPage.Content>

        </ContentPage>
    </MasterDetailPage.Master>

<MasterDetailPage.Detail >
    <ContentPage Padding="10" BackgroundColor="Green">


        </ContentPage>
    </MasterDetailPage.Detail>

using System;
using System.Collections;
using System.Collections.Generic;
using Newtonsoft.Json;
using Xamarin.Forms;

namespace LoginPage
{
public partial class Menu : MasterDetailPage
{
private const string Url = "http://techportsolutions.myddns.me:45152/eKontenService/RestServiceImpl.svc/getServiceData?InputData={0}";
private System.Net.Http.HttpClient client = new System.Net.Http.HttpClient();

    public Menu()
    {
        InitializeComponent();
        getMenu();
        //list_menuPage.ItemTemplate = new DataTemplate(typeof(Models.SubListCell));


    }
    public List<Models.MenuDetails> originalList;
    public List<Models.MenuDetails> topMenuItems;


    async public void getMenu()
    {
        var parameters = new Dictionary<String, String>();
        parameters["iFKCompanyID"] = "20";
        parameters["iFKUserID"] = "55";
        parameters["FK_DOCUMENT_TYPE_ID"] = "0";
        parameters["iFKSalesmanID"] = "0";
        parameters["iFKActorTypeID"] = "0";
        parameters["sAPITemplate"] = "GETROLEMENUS";
        parameters["sAPIValues"] = "|||";
        var menuArray = new List<Dictionary<string, string>>
        {
            parameters
        };
        string obj = JsonConvert.SerializeObject(menuArray, Formatting.Indented);
        var content = await client.GetStringAsync(string.Format(Url, obj));
        originalList = JsonConvert.DeserializeObject <List<Models.MenuDetails>> (content);

        if(originalList!=null)
        {
           topMenuItems = originalList.FindAll(s => s.IS_TOP_MENU == true && s.FK_PARENT_MENU_ID == null);
            list_menuPage.ItemsSource = topMenuItems;
        }


    }

    void Handle_Clicked(object sender, System.EventArgs e)
    {
        if (subListButton.IsVisible == true) // here im trying to use that and facing issue
        {

        }

    }
}

}