Xamarin.Forms：ListView 未在 Xamarin.Droid 上显示

Question

我正在创建 Xamarin.Forms 便携式应用程序。我的 Visual Studio 中有一个数据库，我想将其中的数据显示到 Xamarin ListView。但是每当我这样做时，数据都不会显示在我的 Xamarin.Droid 上，只留下一个空白区域。我在 UWP 中尝试过，它有效。我将如何在我的 Xamarin.Droid 中做到这一点？

（我的 Xamarin.Droid 的屏幕截图）

请注意，即使没有显示所有记录，ListView 仍会占用空间。您认为这背后的原因是什么？如果正在检索数据并且确实如此，我什至会在我的 WEB API 中检查这一点。

意思是，真正的问题只发生在在 ListView 上显示记录。希望你能帮助我。

这是我尝试过的代码。

ClientList.xaml

<?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="XamarinFormsDemo.Views.ClientListPage"
         xmlns:ViewModels="clr-namespace:XamarinFormsDemo.ViewModels;assembly=XamarinFormsDemo"
         xmlns:controls="clr-namespace:ImageCircle.Forms.Plugin.Abstractions;assembly=ImageCircle.Forms.Plugin.Abstractions"
         BackgroundImage="bg3.jpg"
         Title="Client List">


  <ContentPage.BindingContext>
    <ViewModels:CustomerVM/>
  </ContentPage.BindingContext>
  <StackLayout Orientation="Vertical">

    <SearchBar Placeholder="Search" Text="{Binding Keyword}" SearchCommand="{Binding SearchCommand}" x:Name="txtSearch" />

    <ListView ItemsSource="{Binding CustomerList}"
          HasUnevenRows="True">
      <ListView.ItemTemplate>
    <DataTemplate>
      <ViewCell>
        <Grid Padding="10" RowSpacing="10" ColumnSpacing="5">
          <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
          </Grid.RowDefinitions>
          <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition Width="*"/>
          </Grid.ColumnDefinitions>

          <controls:CircleImage Source="icon.png"
                 HeightRequest="66"
                 HorizontalOptions="CenterAndExpand"
                 Aspect="AspectFill"
                 WidthRequest="66"
                 Grid.RowSpan="2"
               />


          <Label Grid.Column="1"
                 Text="{Binding CUSTOMER_NAME}"
                 TextColor="#24e97d"
                 FontSize="24"/>



          <Label Grid.Column="1"
                  Grid.Row="1"
                   Text="{Binding CUSTOMER_CODE}"
                   TextColor="White"
                   FontSize="18"
                   Opacity="0.6"/>


          <Label Grid.Column="1"
              Grid.Row="2"
              Text="{Binding CUSTOMER_CONTACT}"
               TextColor="White"
               FontSize="18"
               Opacity="0.6"/>



        </Grid>
      </ViewCell>
    </DataTemplate>
  </ListView.ItemTemplate>

</ListView>


    <StackLayout Orientation="Vertical"
         Padding="30,10,30,10"
         HeightRequest="20"
         BackgroundColor="#24e97d"
         VerticalOptions="Center"
         Opacity="0.5">
  <Label Text="© Copyright 2016   SMESOFT.COM.PH   All Rights Reserved "
         HorizontalTextAlignment="Center"
         VerticalOptions="Center"
         HorizontalOptions="Center" />
    </StackLayout>
  </StackLayout>

</ContentPage>

ClientListViewModel.cs

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.ComponentModel;
using System.Diagnostics;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Input;
using Xamarin.Forms;
using XamarinFormsDemo.Models;
using XamarinFormsDemo.Services;

namespace XamarinFormsDemo.ViewModels
{
    public class CustomerVM : INotifyPropertyChanged
    {


    private List<Customer> _customerList; // keep all customers
    private List<Customer> _searchedCustomerList; // keep a copy for searching
    private Customer _selectedCustomer = new Customer();

    private string _keyword = "";
    public string Keyword
    {
        get
        {
            return _keyword;
        }
        set
        {
            this._keyword = value;

            // while keyword changed we filter Employees
            //Filter();
        }
    }



    private void Filter()
    {
        if (string.IsNullOrWhiteSpace(_keyword))
        {
            CustomerList = _searchedCustomerList;

        }
        else
        {
            // var lowerKeyword = _keyword.ToLower();
            CustomerList = _searchedCustomerList.Where(r => r.CUSTOMER_NAME.ToLower().Contains(_keyword.ToLower())).ToList();
            //  EmployeesList = _searchedEmployeesList.Where(r => r.EMPLOYEE_NAME.Contains(_keyword)).ToList();


        }
    }




    public List<Customer> CustomerList
    {
        get
        {
            return _customerList;
        }
        set
        {
            _customerList = value;
            OnPropertyChanged();
        }
    }


    public ICommand SearchCommand
    {
        get
        {
            return new Command((sender) =>
            {
                //var searchBar = (SearchBar)sender;
                //this.Keyword = searchBar.Text;
                Filter();
            });
        }
    }



    public CustomerVM()
    {
        InitializeDataAsync();
    }

    private async Task InitializeDataAsync()
    {
        var customerServices = new CustomerServices();
        _searchedCustomerList = await customerServices.GetCustomerAsync();
        CustomerList = await customerServices.GetCustomerAsync();

    }


    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        var handler = PropertyChanged;
        if (handler != null) handler(this, new PropertyChangedEventArgs(propertyName));
    }


    }
}

CustomerService.cs

using Plugin.RestClient;
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using XamarinFormsDemo.Models;

namespace XamarinFormsDemo.Services
{
    public class CustomerServices
    {
    public async Task<List<Customer>> GetCustomerAsync()
    {
        RestClient_Customer<Customer> restClient = new RestClient_Customer<Customer>();

        var customerList = await restClient.GetCustomerAsync();//yung getasync ay pantawag as restclient

        return customerList;
        }


    }
}

RestClient.cs

  public class RestClient_Customer <T>
{


    private const string WebServiceUrl = "http://localhost:50857/api/Customer/";

    public async Task<List<T>> GetCustomerAsync()
    {
        var httpClient = new HttpClient();

        var json = await httpClient.GetStringAsync(WebServiceUrl);

        var taskModels = JsonConvert.DeserializeObject<List<T>>(json);

        return taskModels;
    }
 }

Answer 1

在您的 ViewModel 更改中

public List<Customer> CustomerList

到

public ObservableCollection<Customer> CustomerList

在你的 xaml 中，改变这个

 <ListView ItemsSource="{Binding CustomerList}"

到这里

 <ListView ItemsSource="{Binding CustomerList, Mode=TwoWay}"