[英]Create Observable from non-standard event (no EventArgs / EventHandler)
I would like to create an Observable for an event defined as follows:我想为如下定义的事件创建一个 Observable:
public event Func<Exception, Task> Closed;
The current code I have is this:我目前的代码是这样的:
Observable.FromEvent<Func<Exception, Task>, Unit>(h => hub.Closed += h, h=> hub.Closed -= h);
It compiles OK, but it throws this runtime exception:它编译正常,但它抛出这个运行时异常:
System.ArgumentException: 'Cannot bind to the target method because its signature or security transparency is not compatible with that of the delegate type.'
System.ArgumentException: '无法绑定到目标方法,因为其签名或安全透明度与委托类型不兼容。'
I feel that I'm doing it wrong.我觉得我做错了。 I'm not used to create observables from events that don't follow the EventArgs pattern 😔
我不习惯从不遵循 EventArgs 模式的事件中创建 observable 😔
EDIT: Just for clarification purposes, this is the complete code with how the classic event handling would look:编辑:为了澄清起见,这是经典事件处理的完整代码:
class Program
{
static async Task Main(string[] args)
{
var hub = new HubConnectionBuilder().WithUrl("http://localhost:49791/hubs/status")
.Build();
hub.On<Status>("SendAction", status => Console.WriteLine($"Altitude: {status.Altitude:F} m"));
await hub.StartAsync();
hub.Closed += HubOnClosed;
while (true)
{
}
}
private static Task HubOnClosed(Exception arg)
{
Console.WriteLine("The connection to the hub has been closed");
return Task.CompletedTask;
}
}
You need the conversion overload.您需要转换重载。 I shutter every time I look this thing up:
每次看这个东西我都会关门:
IObservable<TEventArgs> Observable.FromEvent<TDelegate, TEventArgs>(
Func<Action<TEventArgs>, TDelegate> conversion,
Action<TDelegate> addHandler,
Action<TDelegate> removeHandler>
)
So in our case, TEventArgs
is Exception
, and TDelegate
is Func<Exception, Task>
, so you need to convert Action<Exception>
to Func<Exception, Task>>
, in other words: Func<Action<Exception>, Func<Exception, Task>>
.所以在我们的例子中,
TEventArgs
是Exception
,而TDelegate
是Func<Exception, Task>
,所以你需要将Action<Exception>
转换为Func<Exception, Task>>
,换句话说: Func<Action<Exception>, Func<Exception, Task>>
。 I'm assuming that conversion looks like this: a => e => {a(e); return Task.CompletedTask; }
我假设转换看起来像这样:
a => e => {a(e); return Task.CompletedTask; }
a => e => {a(e); return Task.CompletedTask; }
a => e => {a(e); return Task.CompletedTask; }
. a => e => {a(e); return Task.CompletedTask; }
.
System.Reactive needs this conversion function because it needs to subscribe to the event with a proper delegate, and somehow hook in your code/RX Plumbing code. System.Reactive 需要这个转换函数,因为它需要使用适当的委托订阅事件,并以某种方式挂钩您的代码/RX Plumbing 代码。 In this case,
a(e)
is basically RX plumbing which then passes on the Exception to be handled later in the reactive pipeline.在这种情况下,
a(e)
基本上是 RX 管道,然后将异常传递到稍后在反应管道中处理。
Full code:完整代码:
class Program
{
static async Task Main(string[] args)
{
Program.Closed += Program.HubOnClosed;
Observable.FromEvent<Func<Exception, Task>, Exception>(
a => e => {a(e); return Task.CompletedTask; },
h => Program.Closed += h,
h => Program.Closed -= h
)
.Subscribe(e =>
{
Console.WriteLine("Rx: The connection to the hub has been closed");
});
Program.Closed.Invoke(null);
Program.Closed.Invoke(null);
}
private static Task HubOnClosed(Exception arg)
{
Console.WriteLine("The connection to the hub has been closed");
return Task.CompletedTask;
}
public static event Func<Exception, Task> Closed;
}
Does something like this do the trick?这样的事情有用吗?
class Program
{
public event Func<Exception, Task> Closed;
static void Main(string[] args)
{
Program p = new Program();
IObservable<Unit> closedObservable = Observable.Create<Unit>(
observer =>
{
Func<Exception, Task> handler = ex =>
{
observer.OnNext(Unit.Default);
return Task.CompletedTask;
};
p.Closed += handler;
return () => p.Closed -= handler;
});
}
}
Observable.Create()
is a useful fallback for unusual cases like this. Observable.Create()
是处理此类异常情况的有用回退方法。
As an aside, it's very strange to have an event with a non-void returning delegate, since the code that raises the event would only see the value of the last handler to run - unless it raises the event in some non-standard way.顺便说一句,具有非空返回委托的事件非常奇怪,因为引发事件的代码只会看到要运行的最后一个处理程序的值 - 除非它以某种非标准方式引发事件。 But, since it's library code, that's out of your hands!
但是,由于它是库代码,这超出了您的掌握!
Try the following, not using the signature you want but something to try:尝试以下操作,不要使用您想要的签名,而是尝试一些东西:
class Program
{
public delegate void ClosedEventHandler(object sender, Func<Exception, Task> e);
public ClosedEventHandler Closed { get; set; }
static void Main(string[] args)
{
Program hub = new Program();
hub.Closed = hub.SomethingToDoWhenClosed;
Observable
.FromEventPattern<ClosedEventHandler, Func<Exception, Task>>(
h => hub.Closed += h,
h => hub.Closed -= h)
.Subscribe(x =>
{
// this is hit
});
hub.Closed(hub, e => null);
}
public void SomethingToDoWhenClosed(object sender, Func<Exception, Task> e)
{
}
}
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