如何使用 ReactiveList 以便在添加新项目时更新 UI

Question

我正在创建一个带有列表的 Xamarin.Forms 应用程序。 itemSource 是一个响应式列表。但是，将新项目添加到列表不会更新 UI。这样做的正确方法是什么？

列表定义

_listView = new ListView();
var cell = new DataTemplate(typeof(TextCell));
cell.SetBinding(TextCell.TextProperty, "name");
cell.SetBinding(TextCell.DetailProperty, "location");
_listView.ItemTemplate = cell;

绑定

this.OneWayBind(ViewModel, x => x.monkeys, x => x._listView.ItemsSource);
this.OneWayBind(ViewModel, x => x.save, x => x._button.Command); //save adds new items

查看模型

public class MyPageModel : ReactiveObject
{
    public MyPageModel()
    {
        var canSave = this.WhenAny(x => x.username, x => !String.IsNullOrWhiteSpace(x.Value) && x.Value.Length>5);
        save = ReactiveCommand.CreateAsyncTask(canSave, async _ =>
        {
            var monkey = new Monkey { name = username, location = "@ " + DateTime.Now.Ticks.ToString("X"), details = "More here" };
            monkeys.Add(monkey);
            username = "";
        });
        monkeys = new ReactiveList<Monkey>{
            new Monkey { name="Baboon", location="Africa & Asia", details = "Baboons are Africian and Arabian Old World..." }
        };
        _monkeys.ChangeTrackingEnabled = true;
    }
    private string _username = "";
    public string username
    {
        get { return _username; }
        set { this.RaiseAndSetIfChanged(ref _username, value); }
    }
    private double _value = 0;
    public double value
    {
        get { return _value; }
        set { this.RaiseAndSetIfChanged(ref _value, value); }
    }
    public ReactiveCommand<Unit> save { get; set; }
    public ReactiveList<Monkey> _monkeys;
    public ReactiveList<Monkey> monkeys
    {
        get { return _monkeys; }
        set { this.RaiseAndSetIfChanged(ref _monkeys, value); }
    }
}
public class Monkey
{
    public string name { get; set; }
    public string location { get; set; }
    public string details { get; set; }
}

尝试将 ReactiveList 属性作为正常的自动属性以及上面代码中我使用 RaiseAndSetIfChanged 方法的属性。

Answer 1

您的问题是您在非 UI 线程上更改 monkeys。在其他框架中，这会抛出异常，但在 AppKit / UIKit 中，这只是做奇怪的事情（通常什么都没有）。

    save = ReactiveCommand.Create(canSave);
    save.Subscribe(_ =>
    {
        // Do the part that modifies UI elements (or things bound to them)
        // in the RxCmd's Subscribe. This is guaranteed to run on the UI thread
        var monkey = new Monkey { name = username, location = "@ " + DateTime.Now.Ticks.ToString("X"), details = "More here" };
        monkeys.Add(monkey);
        username = "";
    });

Answer 2

这种技术看起来非常复杂。这让我觉得你想做一些我认为更复杂的事情。

这是一个干净的解决方案，通过以纯 MVVM 方式绑定到 ReactiveList<T>，将对象添加到列表框。

首先，xaml

<Window x:Class="ReactiveUIListBox.View.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:viewModel="clr-namespace:ReactiveUIListBox.ViewModel"
        Title="MainWindow" Height="350" Width="525">

    <Window.Resources>
        <viewModel:MainWindowViewModel x:Key="MainWindowViewModel"/>    
    </Window.Resources>

    <Window.DataContext>
        <StaticResource ResourceKey="MainWindowViewModel"/>
    </Window.DataContext>

    <Grid DataContext="{StaticResource MainWindowViewModel}">
        <Grid.ColumnDefinitions>
            <ColumnDefinition/>
            <ColumnDefinition/>
        </Grid.ColumnDefinitions>

        <Grid Grid.Column="0" Background="Azure">
            <ListBox ItemsSource="{Binding Model.TestReactiveList}"></ListBox>
        </Grid>

        <Grid Grid.Column="1">
            <Button x:Name="button" Command="{Binding TestCommand}" Content="Button" HorizontalAlignment="Left" Margin="78,89,0,0" VerticalAlignment="Top" Width="75"/>
        </Grid>

    </Grid>
</Window>

这是视图模型

using System.Windows.Input;
using ReactiveUIListBox.Model;
using SecretSauce.Mvvm.ViewModelBase;

namespace ReactiveUIListBox.ViewModel
{
    public class MainWindowViewModel : ViewModelBase
    {
        public MainWindowViewModel()
        {
            Model = new ReactiveModel<string>();
        }
        public ReactiveModel<string> Model
        {
            get;
            set;
        }

        public ICommand TestCommand
        {
            get { return new RelayCommand(ExecuteTestCommand); }
        }

        private void ExecuteTestCommand(object obj)
        {
            Model.TestReactiveList.Add("test string");
        }
    }
}

最后，这是模型。

using ReactiveUI;

namespace ReactiveUIListBox.Model
{
    public class ReactiveModel<T> : ReactiveObject
    {
        public ReactiveModel()
        {
            TestReactiveList= new ReactiveList<T>();
        }

        public ReactiveList<T> TestReactiveList
        {
            get;
            set;
        }
    }
}

按下按钮将填充列表框。希望我没有完全简化您尝试做的事情，但是您的代码似乎到处都是。

我无法区分适合视图、模型或视图模型的代码。

干杯。