Question

假设我有以下视图模型：

public class AddressViewModel : ReactiveObject
{
    private string line;

    public string Line
    {
        get { return this.line; }
        set { this.RaiseAndSetIfChanged(x => x.Line, ref this.line, value); }
    }
}

public class EmployeeViewModel : ReactiveObject
{
    private AddressViewModel address;

    public AddressViewModel Address
    {
        get { return this.address; }
        set { this.RaiseAndSetIfChanged(x => x.Address, ref this.address, value); }
    }
}

现在假设在EmployeeViewModel中我希望公开一个具有最新值Address.Line的属性：

public EmployeeViewModel()
{
    this.changes = this.ObservableForProperty(x => x.Address)
        .Select(x => x.Value.Line)
        .ToProperty(this, x => x.Changes);
}

private readonly ObservableAsPropertyHelper<string> changes;
public string Changes
{
    get { return this.changes.Value; }
}

只有在对Address属性进行更改时才会勾选，但在Line内发生Address更改时则不会。如果我这样做：

public EmployeeViewModel()
{
    this.changes = this.Address.Changed
        .Where(x => x.PropertyName == "Line")
        .Select(x => this.Address.Line)        // x.Value is null here, for some reason, so I use this.Address.Line instead
        .ToProperty(this, x => x.Changes);
}

仅当当前Line内的AddressViewModel发生更改时才会勾选，但不会考虑完全设置新的AddressViewModel（也不会容纳null 1}} Address）。

我正试图找到解决这个问题的正确方法。我是RxUI的新手，所以我可能会遗漏一些明显的东西。我可以手动挂钩地址更改并设置辅助订阅，但这看起来很丑陋且容易出错。

我应该使用标准模式或助手来实现这一目标吗？

以下是一些可以复制/粘贴的代码：

ViewModels.cs ：

namespace RxUITest
{
    using System;
    using System.Reactive.Linq;
    using System.Threading;
    using System.Windows.Input;
    using ReactiveUI;
    using ReactiveUI.Xaml;

    public class AddressViewModel : ReactiveObject
    {
        private string line1;

        public string Line1
        {
            get { return this.line1; }
            set { this.RaiseAndSetIfChanged(x => x.Line1, ref this.line1, value); }
        }
    }

    public class EmployeeViewModel : ReactiveObject
    {
        private readonly ReactiveCommand changeAddressCommand;
        private readonly ReactiveCommand changeAddressLineCommand;
        private readonly ObservableAsPropertyHelper<string> changes;
        private AddressViewModel address;
        private int changeCount;

        public EmployeeViewModel()
        {
            this.changeAddressCommand = new ReactiveCommand();
            this.changeAddressLineCommand = new ReactiveCommand();

            this.changeAddressCommand.Subscribe(x => this.Address = new AddressViewModel() { Line1 = "Line " + Interlocked.Increment(ref this.changeCount) });
            this.changeAddressLineCommand.Subscribe(x => this.Address.Line1 = "Line " + Interlocked.Increment(ref this.changeCount));

            this.Address = new AddressViewModel() { Line1 = "Default" };

            // Address-only changes
            this.changes = this.ObservableForProperty(x => x.Address)
                .Select(x => x.Value.Line1 + " CHANGE")
                .ToProperty(this, x => x.Changes);

            // Address.Line1-only changes
            //this.changes = this.Address.Changed
            //    .Where(x => x.PropertyName == "Line1")
            //    .Select(x => this.Address.Line1 + " CHANGE")        // x.Value is null here, for some reason, so I use this.Address.Line1 instead
            //    .ToProperty(this, x => x.Changes);
        }

        public ICommand ChangeAddressCommand
        {
            get { return this.changeAddressCommand; }
        }

        public ICommand ChangeAddressLineCommand
        {
            get { return this.changeAddressLineCommand; }
        }

        public AddressViewModel Address
        {
            get { return this.address; }
            set { this.RaiseAndSetIfChanged(x => x.Address, ref this.address, value); }
        }

        public string Changes
        {
            get { return this.changes.Value; }
        }
    }
}

MainWindow.cs ：

using System.Windows;

namespace RxUITest
{
    public partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();

            this.DataContext = new EmployeeViewModel();
        }
    }
}

MainWindow.xaml ：

<Window x:Class="RxUITest.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">
    <StackPanel>
        <TextBlock Text="{Binding Changes}"/>
        <Button Command="{Binding ChangeAddressCommand}">Change Address</Button>
        <Button Command="{Binding ChangeAddressLineCommand}">Change Address.Line1</Button>
    </StackPanel>
</Window>

Answer 1

不，有一种更简单的方法可以做到这一点：

this.WhenAny(x => x.Address.Line, x => x.Value)
    .Subscribe(x => Console.WriteLine("Either Address or Address.Line changed!"));

Answer 2

如果您认为您的地址可以是简单的行集合，即

class AddressViewModel 
 : ObservableCollection<LineViewModel>, INotifyPropertyChanged

然后您可能会附加一个事件处理程序来传播更改

this.CollectionChanged += this.NotifyPropertyChanged(...);

所以我会为ReactiveObject做同样的事情，但是使用Rx

public class EmployeeViewModel : ReactiveObject
{
private AddressViewModel address;
private IDisposable addressSubscription;

public AddressViewModel Address
{
    get { return this.address; }
    set 
    { 
        if (addressSubscription != null)
        {
            addressSubscription.Dispose();
            addressSubscription =null;
        }
        if (value != null)
        {
            addressSubscription = value.Subscribe(...);
        }
        this.RaiseAndSetIfChanged(x => x.Address, ref this.address, value); 
     }
}

}

是否存在使用Reactive UI订阅分层属性更改的模式？

2 个答案: