从 ModalAsync 中更新 ObservableCollection

如何解决从 ModalAsync 中更新 ObservableCollection

我有一个需要从推送的 modalasync 更新的 observable 集合。可观察集合基本上是一个购物车。在主页 (MyHome.xaml.cs) 中，我有另一个 observable 集合，当单击项目时，会将模态异步推送到 selctionPage(SelectionPage.xaml.cs)。在此选择页面中，我将一个项目添加到位于 MyHome.xaml 的 Cart 可观察集合中。

我的问题是当我们回去查看购物车时，集合没有更新。我曾尝试在 pushModalAsync 期间发送 MyHomePage 和实际的 Cart ，但这些都不起作用。我还尝试从模态异步中调用 MyHome 函数，但也不起作用。

MyHome.xaml.cs

using System;
using System.Collections;
using System.Collections.Generic;
using HW3.viewmodel;
using HW3.Model;

using Xamarin.Forms;
using System.Collections.ObjectModel;

namespace HW3.Views
{
    public partial class MyHome : ContentPage
    {

       
        public ObservableCollection<Product> Cart { get; set; }
        
        Product jello = new ProductByQuantity(1.00,3,"Jello","Canned & Packaged Foods",0001);

        public MyHome()
        {
            InitializeComponent();
            BindingContext = new Productviewmodel();

            //Cart = new ObservableCollection<Product>();
            //Cart.Add(jello);
            //Cart.Add(jello);

            //add(jello);

        }

        private async void OnItemSelected(Object sender,ItemTappedEventArgs e)
        {
            
            //add(e.Item as Product);
            if (e.Item is ProductByWeight)
            {
                var extra = e.Item as ProductByWeight;
                var details = e.Item as Product;

                
                await Navigation.PushModalAsync(new SelectionPage(details.Name,details.Price,details.Description,details.ID,extra.getounces(),extra,Cart,this));
            }
            else if(e.Item is ProductByQuantity)
            {
                var extra = e.Item as ProductByQuantity;
                var details = e.Item as Product;

                //Navigation.PushModalAsync(new NavigationPage(new SelectionPage(details.Name,extra.getUnits(),this)));
                await Navigation.PushModalAsync(new SelectionPage(details.Name,this));
            }

        }

        public void add(Product p)
        {
            
            
        }

    };

}

SelectionPage.xaml.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using HW3.Model;
using HW3.viewmodel;
using Xamarin.Forms;

namespace HW3.Views
{
    public partial class SelectionPage : ContentPage
    {

        MyCartviewmodel myCartviewmodel = new MyCartviewmodel();
        ObservableCollection<Product> pr;
        MyHome Home;
        Product chicken = new ProductByWeight(12.50,75,"Chicken Breast","Produce",0016);
        public ObservableCollection<Product> Cart1 { get; set; }

        public SelectionPage(string Name,double Price,string Description,int ID,double units_ounces,Product product,ObservableCollection<Product> p,MyHome home)
        {
            InitializeComponent();

            //property equal cart here

            testName.Text = product.Name;
            testPrice.Text = "Price: $" + Price.ToString();
            testInventory.Text = "Inventory: " + units_ounces.ToString();
            testDescription.Text = Description;
            slider.Minimum = 1;
            slider.Maximum = units_ounces;
            sliderNumber.Text = "Value: 1";
            pr = p;
            Home = home;
            

        }

        private void slider_changed(object sender,ValueChangedEventArgs e)
        {
            var newStep = Math.Round(e.NewValue / 1.0);

            slider.Value = newStep * 1.0;
            sliderNumber.Text = "Value: " + slider.Value;
        }

        private async void addButton_clicked(Object sender,System.EventArgs e)
        {
            string str = sliderNumber.Text;
            var result = str.Substring(str.LastIndexOf(" ") + 1);
            
            var chicken = new ProductByWeight(12.50,0016);

            //Home.Cart.Add(chicken);
            //Home.add(chicken);
            //pr.Add(chicken);

            Cart1 = new ObservableCollection<Product>();
            Cart1.Add(chicken);
            
            Home.Cart = new ObservableCollection<Product>();
            Home.Cart = Cart1;
            foreach(Product x in Home.Cart)
            {
                Console.WriteLine("Hello " + x.Name);
            }

        }
        private async void backButton_clicked(Object sender,System.EventArgs e)
        {
            var chicken = new ProductByWeight(12.50,0016);
            //Home.add(chicken);
            //Home.Cart.Add(chicken);
            //pr.Add(chicken);
            Navigation.PopModalAsync();
        }
    }
}

MyCart.xaml.cs

using System;
using System.Collections.Generic;
using HW3.Model;
using HW3.viewmodel;

using Xamarin.Forms;

namespace HW3.Views
{
    public partial class MyCart : ContentPage
    {
        public List<Product> myCart1 = new List<Product>();

        public MyCart()
        {
            InitializeComponent();
            this.BindingContext = new MyHome();
            
        }

       
    }
}

在此先感谢所有提供帮助的人！我已经坚持了一段时间。

解决方法

在 SelectionPage 中，您传入对 Cart ObservableCollection 的引用，但您从未对它进行任何操作。您应该能够添加项目，它们将反映在 MyHome 中，因为它们引用相同的对象。在您的代码中还有几个地方可以创建新对象 - 任何时候您都会获得一个类的新副本，该副本与代码中其他地方使用的副本没有任何联系，并且不会更新该新副本反映在其他页面

更好的方法是将 Cart 创建为 App 类的属性，以便可以从应用的每个页面轻松访问它