c# - 如何修复 xamarin.forms 移动应用程序页面中的空 ListView

Question

我正在学习将 Xamarin.Forms 与 prism 结合使用，我想用列表中每个对象的特定项目填充 ListView 。我的 ListView 显示为空，但我没有看到任何错误。

我已经尝试使用绑定(bind)来绑定(bind)到我的对象中的 Name 变量，在我的列表中。它显示为空，所以我尝试使用 Observable Collection 来获取我的列表并添加每个名称。

这是动物对象模型

using System;
namespace LearningPrism.Models
{
    class Animal
    {
        public string Name { get; set; }
        public int Age { get; set; }
        public decimal Happiness { get; set; }

        public void PrintBase()
        {
            Console.WriteLine($"Name: {Name}");
            Console.WriteLine($"Age: {Age}");
            Console.WriteLine($"Happy: {Happiness}");
            Console.WriteLine();
        }
    }
}

我使用 Breed 类作为对象创建我的列表，并有 3 个函数用于获取类型的过滤列表(未过滤以获取所有品种)。

namespace LearningPrism.Models
{
    class Breed
    {

        public static List<Animal> _breedList = new List<Animal>
            {
                new Animal
                {
                    Id = Guid.NewGuid().ToString(),
                    Name = "Greyhound",
                    Type = BreedType.Dog
                },

//There are 3 more Dog Animal breeds but I have removed them so it is easier to read

                new Animal
                {
                    Id = Guid.NewGuid().ToString(),
                    Name = "Bengal",
                    Type = BreedType.Cat
                }, 

//There are 3 more Cat Animal breeds but I have removed them so it is easier to read

                }
            };

        public static List<Animal> GetAllBreeds()
        {
            return _breedList;
        }

        public static List<Animal> GetBreedsByType(BreedType type)
        {

            switch (type)
            {
                case BreedType.Dog:
                    return (from Animal in _breedList where Animal.Type == BreedType.Dog select Animal).ToList();

                case BreedType.Cat:
                    return (from Animal in _breedList where Animal.Type == BreedType.Cat select Animal).ToList();

                default:
                    return _breedList;

            }
        }
    }
}

这是我的 View 模型:

namespace LearningPrism.ViewModels
{
    public class PageAViewModel : ViewModelBase
    {
        private List<Breed> MyList { get; set; }

        public PageAViewModel(INavigationService navigationService) : base(navigationService)
        {
            Title = "Hello Human";
        }

        private void LoadData()
        {

            ObservableCollection<Animal> myData = new ObservableCollection<Animal>(Breed.GetAllBreeds() as List<Animal>);

        }

        public override void OnNavigatingTo(INavigationParameters parameters)
        {
            base.OnNavigatingTo(parameters);

            LoadData();
        }
    }
}

这是页面的 XAML 代码

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:prism="clr-namespace:Prism.Mvvm;assembly=Prism.Forms"
             prism:ViewModelLocator.AutowireViewModel="True"
             x:Class="LearningPrism.Views.PageA" Title="{Binding Title}">

    <Label Text="{Binding Title}" HorizontalOptions="CenterAndExpand" VerticalOptions="CenterAndExpand" />

    <StackLayout>

        <ListView HorizontalOptions="FillAndExpand" 
                  VerticalOptions="FillAndExpand" 
                  ItemsSource="{Binding myData}">

            <ListView.ItemTemplate>
                <DataTemplate>
                    <StackLayout HorizontalOptions="CenterAndExpand">
                        <Label Text="{Binding Breed.Name}" TextColor="Black"></Label>
                    </StackLayout>
                </DataTemplate>
            </ListView.ItemTemplate>

        </ListView>

    </StackLayout>

</ContentPage>

Answer 1

首先，要将您的 ListView 绑定(bind)到 myData，myData 必须是公共(public)属性。

public ObservableCollection<Animal> myData { get; set; }

如果列表中的每一项都是Animal，那么您的绑定(bind)路径将为Text="{Binding Name}"，因为Name是 Animal 的属性。没有 Breed 属性。