c# - 反应式扩展处置事件处理程序

Question

大家好，我有一个 ExternalDataService 不断发射实时数据，它包含在一个库中。

我有一个包装类，它订阅并将更新放在 Observable 上。

   public class MyService
    {
        private ExternalDataService _externalDataService;

    public MyService()
    {
        _externalDataService= new ExternalDataService ();
    }


    public IObservable<double> GetData()
    {
        return Observable.Create<double>(i => 
        {   
            _externalPriceService.OnDataChanged += (s, e) => { i.OnNext(e); };


            return () => 
            {
              //  what do I do here?
            };
        });
    }    

}

作为消费...

var p = new MyService();

var disposable = p.GetData().Subscribe(i => Console.WriteLine(i));

_externalPriceService.OnDataChanged当Dispose调用一次性时，我将如何取消订阅 ？

Answer 1

使用 Observable.FromEvent 或 Observable.FromEventPattern，而不是 Observable.Create。然后你只需 Dispose 订阅。

根据您的 EventHandler 定义，它会是这样的：

public class ExternalDataService {
    public EventHandler<DataChangedEventArgs> OnDataChanged;    
}

public class DataChangedEventArgs : EventArgs {
    public Double Data {
        get; set;
    }
}

public class MyService {
    private ExternalDataService _externalDataService;
    public MyService()
    {
        _externalDataService= new ExternalDataService ();
    }
    public IObservable<double> GetData()
    {
        return Observable.FromEventPattern<DataChangedEventArgs>(eh => _externalDataService.OnDataChanged += eh, eh => _externalDataService.OnDataChanged -= eh)
            .Select(e => e.EventArgs.Data);
    }       
}

Answer 2

你也可以这样做：

public IObservable<double> GetData()
{
    Action<object, double> dataHandler = null;
    return Observable.Create<double>(i => 
    {   
        dataHandler = (s, e) => { i.OnNext(e); };;
        _externalDataService.OnDataChanged += dataHandler;
        return Disposable.Create(() => 
        {
            _externalDataService.OnDataChanged -= dataHandler;
        });
    });
}    

编辑：愚蠢的错别字