在Xamarin.Forms中使用Rx.Net：OnNext事件未触发问题排查

问题场景 #

希望将Rx.Net的Subject封装在独立的RxNetHandler类中，实现多类共享，但MainPage中的订阅始终无法接收OnNext事件。若将Subject直接放在InfoStorageService类中则可正常工作，需要解决实例共享的问题。

代码示例 #

RxNetHandler类 #

public class RxNetHandler
{
    public readonly ReplaySubject<List<InfoDto>> InfoSubject = new(1);
}

InfoStorageService类 #

public class InfoStorageService
{
    private readonly RxNetHandler _rxNetHandler = new();
    private HttpClient _httpClient;
    private List<InfoDto> _infos = new();

    public InfoStorageService()
    {
        InitHttps();
    }

    public async Task GetInfosDetails()
    {
        var response = await _httpClient.GetAsync("https://jsonplaceholder.typicode.com/posts?userId=1");
        var content = response.Content;

        if (response.IsSuccessStatusCode)
        {
            var jsonResponse = await content.ReadAsStringAsync();
            _infos = JsonConvert.DeserializeObject<List<InfoDto>>(jsonResponse);
        }
        else
        {
            throw new Exception(((int)response.StatusCode).ToString() + " - " + response.ReasonPhrase);
        }

        _rxNetHandler.InfoSubject.OnNext(_infos);
    }
 }

MainPage类 #

public partial class MainPage : ContentPage
{
    private readonly RxNetHandler _rxNetHandler = new();
    private readonly InfoStorageService _infoStorage = new();
    private List<InfoDto> _infos = new();
    private IDisposable _disposed;

    public MainPage()
    {
        InitializeComponent();
        InitData();
    }

    protected override void OnAppearing()
    {
        _disposed = _rxNetHandler.InfoSubject.Subscribe(
            infos =>
            {
                _infos = infos;
            },
            () =>
            {
                Console.WriteLine("[ completed ]");
            }
        );
    }

    private async void InitData()
    {
        await _infoStorage.GetInfosDetails();
        InfoListView.ItemSelected += InfoListOnItemSelected;
    }
}

问题原因 #

核心问题是RxNetHandler实例不共享：
InfoStorageService和MainPage各自通过new()创建了独立的RxNetHandler对象，两者的InfoSubject是完全分离的实例。InfoStorageService调用OnNext时，是在自己的Subject上发送消息，而MainPage订阅的是另一个完全无关的Subject，因此无法接收到消息。

解决方案 #

方案1：单例模式确保实例唯一 #

修改RxNetHandler为单例，让所有类共享同一个实例：

public class RxNetHandler
{
    private RxNetHandler() {}
    public static RxNetHandler Instance { get; } = new RxNetHandler();
    public readonly ReplaySubject<List<InfoDto>> InfoSubject = new(1);
}

修改InfoStorageService和MainPage的引用方式：

• InfoStorageService中：private readonly RxNetHandler _rxNetHandler = RxNetHandler.Instance;
• MainPage中：private readonly RxNetHandler _rxNetHandler = RxNetHandler.Instance;

方案2：依赖注入传递实例 #

如果项目使用依赖注入（如.NET MAUI的内置DI），将RxNetHandler注册为单例：
在Program.cs中添加：

builder.Services.AddSingleton<RxNetHandler>();

修改类的构造函数实现注入：

// InfoStorageService构造函数
public InfoStorageService(RxNetHandler rxNetHandler)
{
    _rxNetHandler = rxNetHandler;
    InitHttps();
}

// MainPage构造函数
public MainPage(RxNetHandler rxNetHandler, InfoStorageService infoStorage)
{
    _rxNetHandler = rxNetHandler;
    _infoStorage = infoStorage;
    InitializeComponent();
    InitData();
}

方案3：手动传递同一实例 #

在MainPage中创建RxNetHandler实例，传递给InfoStorageService：

// MainPage构造函数
public MainPage()
{
    _rxNetHandler = new RxNetHandler();
    _infoStorage = new InfoStorageService(_rxNetHandler);
    InitializeComponent();
    InitData();
}

// InfoStorageService构造函数
public InfoStorageService(RxNetHandler rxNetHandler)
{
    _rxNetHandler = rxNetHandler;
    InitHttps();
}

内容的提问来源于stack exchange，提问作者JBD