使用类时未填充 Xamarin 列表视图

Question

我目前正在尝试学习 Xamarin.forms，但我被困在课程的当前部分。

我手动创建了一个列表视图，并被告知将其转换为单独类中的“远程服务”。

当我这样做时，列表不再填充，我无法弄清楚我做错了什么。编译时出现零错误。

放置在名为“SearchServices.cs”的类中的“远程服务”代码如下所示：

using System;
using System.Collections.Generic;
using System.Linq;
using ListExcercises.Models;

namespace ListExcercises.Services
{
    public class SearchServices
    {
        private List<Search> _searches = new List<Search>
        {
            new Search
            {
                Id=1,
                Location = "West Hollywood, CA, United States",
                CheckIn = new DateTime(2016, 9, 1),
                CheckOut = new DateTime(2016, 11, 1)
            },

            new Search
            {
                Id=2,
                Location ="Santa Monica, CA, United States",
                CheckIn = new DateTime(2016, 9, 1),
                CheckOut = new DateTime(2016, 11, 1)
            }
        };



        public IEnumerable<Search> GetRecentSearches(string filter = null)
        {
            if (String.IsNullOrWhiteSpace(filter))
                return _searches;
            return _searches.Where(s => s.Location.StartsWith(filter, StringComparison.CurrentCultureIgnoreCase));

        }


        public void DeleteSearch(int searchId){
            _searches.Remove(_searches.Single(s => s.Id == searchId));
        }
    

视图背后的代码如下所示：

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using ListExcercises.Models;
using ListExcercises.Services;
using Xamarin.Forms;

namespace ListExcercises
{

    public partial class ExcerciseListPage : ContentPage
    {
        private SearchServices _searchService;
        private List<SearchGroup> _searchGroups;

        public ExcerciseListPage()
        {
            _searchService = new SearchServices();

            InitializeComponent();

            PopulateListView(_searchService.GetRecentSearches());
            
        }
        //Create re-usable list grouping(populate list)
        private void PopulateListView(IEnumerable<Search> searches)
        {
            _searchGroups = new List<SearchGroup>
            {
                new SearchGroup("Recent Searches", searches)
            };

            listView.ItemsSource = _searchGroups;

        }
        void onItemTap(object sender, Xamarin.Forms.ItemTappedEventArgs e)
        {
            var search = e.Item as Search;
            DisplayAlert("Tapped",
                "Costumer visited " + search.Location + " at " + search.CheckIn + " and left at " + search.CheckOut,
                "OK");
        }

        void listView_ItemSelected(System.Object sender, Xamarin.Forms.SelectedItemChangedEventArgs e)
        {
            listView.SelectedItem = null;
        }

        void Delete_Clicked(System.Object sender, System.EventArgs e)
        {
            var search = (sender as MenuItem).CommandParameter as Search;

            //Delete local
            _searchGroups[0].Remove(search);

            //Update backend
            _searchService.DeleteSearch(search.Id);

        }

        void listView_Refreshing(System.Object sender, System.EventArgs e)
        {
            PopulateListView(_searchService.GetRecentSearches(searchBar.Text));

            listView.EndRefresh();
        }

        void searchBar_TextChanged(Object sender, Xamarin.Forms.TextChangedEventArgs e)
        {
            PopulateListView(_searchService.GetRecentSearches(e.NewTextValue));
            }

        
    }
}

XAML 代码如下所示：

<?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="ListExcercises.ExcerciseListPage">
<StackLayout Padding="0, 40, 0, 0">
    <SearchBar Placeholder="Search..."
               Margin="0"
               HorizontalOptions="Fill"
               x:Name="searchBar"
               TextChanged="searchBar_TextChanged"/>

    <StackLayout>
    <ListView x:Name="listView" IsGroupingEnabled="True" HasUnevenRows="True"
              GroupDisplayBinding="{Binding Title}"
              ItemTapped="onItemTap"
              ItemSelected="listView_ItemSelected"
              IsPullToRefreshEnabled="True"
              Refreshing="listView_Refreshing">
           

            <ListView.GroupHeaderTemplate>
                
                <DataTemplate>
                    <ViewCell>
                         

                        <Label Padding="20,0,0,0" Text="{Binding Title}"
                               FontSize="21"
                               HorizontalOptions="StartAndExpand"
                               VerticalOptions="Center"
                               FontAttributes="Bold"/>
                    </ViewCell>
                </DataTemplate>
            </ListView.GroupHeaderTemplate>


            

            <ListView.ItemTemplate>
                <DataTemplate>

                    <ViewCell>
                        <ViewCell.ContextActions>

                            <MenuItem Text="Delete" Clicked="Delete_Clicked"
                                      IsDestructive="True" />

                        </ViewCell.ContextActions>
                        <StackLayout Padding="20, 0, 0, 0">
                            <Label Text="{Binding Location}" FontSize="20"/>
                            <StackLayout Orientation="Horizontal">
                                <Label Text="{Binding CheckIn, StringFormat='{0:MMM d, yyyy}'}"
                                       TextColor="CornflowerBlue" FontSize="13"/>
                                <Label Text="-" TextColor="CornflowerBlue"
                                       FontSize="13"/>
                                <Label Text="{Binding CheckOut, StringFormat='{0:MMM d, yyyy}'}"
                                       TextColor="CornflowerBlue"  FontSize="13"/>
                            </StackLayout>


                        </StackLayout>


                    </ViewCell>
                </DataTemplate>

            </ListView.ItemTemplate>




        </ListView>
        </StackLayout>
</StackLayout>

除了上面发布的代码之外，我还找到了模型，一个叫做 Search.cs，一个叫做 SearchGroup.cs。两者都放在项目的Models文件夹中。

SearchGroup 中的代码如下所示：

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;

namespace ListExcercises.Models
{
    public class SearchGroup : ObservableCollection<Search> { 

        public string Title { get; set; }


        public SearchGroup(string title, IEnumerable<Search> searches)
        {
            Title = title;
        }
    }
}

最后搜索的代码是这样的：

using System;
namespace ListExcercises.Models
{
    public class Search
    {
        public int Id { get; set; }
        public string Location { get; set; }
        public DateTime CheckIn { get; set; }
        public DateTime CheckOut { get; set; }
        public string Period
        {
            get
            {
                return String.Format("{0} - {1}",
                    CheckIn.ToString("MMM d, yyyy"),
                    CheckOut.ToString("MMM d, yyyy"));
            }
        }
    }
}

我真的希望有人可以帮助我并给我一些指示。

TL;DR：
尝试将列表创建移动到单独的文档/类，现在我的列表视图没有填充信息。所以我可以看到大部分功能都在那里，但是所有行都是空的。

Answer 1

你的构造函数需要调用基础构造函数

public SearchGroup(string title, IEnumerable<Search> searches) : base(searches)
{
   Title = title;
}