Shopping Cart Quantity not getting incremented - xamarin.ios

Question

We are developing an iOS shopping cart application in c# and visual studio for xamarin we are using listview for displaying items and quantity text box, next to the quantity entry box we placed two button plus and minus to increase and decrease the quantity.
We are able to see the quantity and the button in the listview, but when we click on + button quantity is not getting incremented and same with - button.
Request you to help us to resolve this issue and we are pasting code below
c# code
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Xamarin.Forms;
using Xamarin.Forms.Xaml;
using System.Collections.ObjectModel;
using ShopApp.Models;
using System.Reflection;
using System.IO;
using ShopApp.Views;
using Newtonsoft.Json;
using System.Diagnostics;
using System.Windows.Input;
namespace ShopApp.SalesOrderPages
{
[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class AllItems : ContentPage
{
ObservableCollection<Catalogcls> employees = new ObservableCollection<Catalogcls>();
public AllItems()
{
InitializeComponent();
var assembly = typeof(LoadResourceText).GetTypeInfo().Assembly;
Stream stream = assembly.GetManifestResourceStream("ShopApp.Catalog_Master.json");
Catalogcls[] CatalogObj;
using (var reader = new StreamReader(stream))
{
var json = reader.ReadToEnd();
var jsondeserilize = JsonConvert.DeserializeObject<RootObject2>(json);
CatalogObj = jsondeserilize.Catalog;
}
for (int i = 0; i < CatalogObj.Length; i++)
{
employees.Add(new Catalogcls
{
Image = CatalogObj[i].Image,
Name = CatalogObj[i].Name,
Pack = CatalogObj[i].Pack,
Price = CatalogObj[i].Price,
UnitPrice = CatalogObj[i].UnitPrice
});
lstView.ItemsSource = employees;
}
}
}
}
Models
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ShopApp.Models
{
public class Catalogcls
{
public string Type { get; set; }
public string Image { get; set; }
public string Name { get; set; }
public double UnitPrice { get; set; }
public string Price { get; set; }
public string Pack { get; set; }
}
public class RootObject2
{
public Catalogcls[] Catalog { get; set; }
}
}
Xaml code
<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
x:Class="ShopApp.SalesOrderPages.AllItems">
<StackLayout Orientation="Vertical">
<Label Text="ListView" FontSize="60" ></Label>
<ListView x:Name="lstView" HasUnevenRows="True" >
<ListView.Header>
<StackLayout Orientation="Horizontal" HorizontalOptions="FillAndExpand" >
<StackLayout Orientation="Vertical" HorizontalOptions="EndAndExpand" >
<Label Text="Total:" FontSize="15" TextColor="Black" />
</StackLayout>
<StackLayout Orientation="Vertical" HorizontalOptions="EndAndExpand" Padding="0,0,20,0">
<Image Source="cart.png" x:Name="CartImage" Opacity="0.5" AnchorX="0.5" AnchorY="0.5" HeightRequest="40">
</Image>
<Button WidthRequest="100" HeightRequest="20" Text="Nextpage"></Button>
</StackLayout>
</StackLayout>
</ListView.Header>
<ListView.ItemTemplate>
<DataTemplate>
<ViewCell>
<StackLayout Orientation="Horizontal" >
<Grid Padding="20">
<Image Source="{Binding Image}" WidthRequest="100" HeightRequest="100"/>
</Grid>
<StackLayout Orientation="Vertical" Padding="20" >
<StackLayout>
<Label Text="{Binding Name}" FontSize="15" TextColor="Black" />
<Label Text="{Binding Price}" FontSize="15" TextColor="Black" />
<Label Text="{Binding Pack}" FontSize="15" TextColor="Black" />
<Label Text="{Binding UnitPrice}" FontSize="15" TextColor="Black" />
</StackLayout>
<StackLayout Orientation="Horizontal" HorizontalOptions="FillAndExpand" VerticalOptions="Center">
<StackLayout Orientation="Vertical">
<Button WidthRequest="60" HeightRequest="20" Text="-" Command="{Binding DecreaseQuantityCommand}" TextColor="Black"></Button>// on click of - button not able bind value for entrybox
</StackLayout>
<StackLayout Orientation="Vertical" >
<Entry WidthRequest="40" HeightRequest="20" Text="{Binding Quantity, Mode=TwoWay}" ></Entry>
</StackLayout>
<StackLayout Orientation="Vertical">
<Button WidthRequest="60" HeightRequest="20" Text="+" Command="{Binding IncreaseQuantityCommand}" TextColor="Black" ></Button>
</StackLayout>
</StackLayout>
</StackLayout>
</StackLayout>
</ViewCell>
</DataTemplate>
</ListView.ItemTemplate>
</ListView>
</StackLayout>
</ContentPage>