题
我和我的第一个简单的“Hello World” RX应用挣扎。我使用VS2010 RC,再加上最新的RX下载。
以下是简单的控制台应用程序;
class Program
{
static void Main(string[] args)
{
var channel = new MessageChannel()
.Where(m => m.process)
.Subscribe((MyMessage m) => Console.WriteLine(m.subject));
//channel.GenerateMsgs();
}
}
public class MyMessage
{
public string subject;
public bool process;
}
public class MessageChannel: IObservable<MyMessage>
{
List<IObserver<MyMessage>> observers = new List<IObserver<MyMessage>>();
public IDisposable Subscribe(IObserver<MyMessage> observer)
{
observers.Add(observer);
return observer as IDisposable;
}
public void GenerateMsgs()
{
foreach (IObserver<MyMessage> observer in observers)
{
observer.OnNext(new MyMessage() {subject = "Hello!", process = true});
}
}
}
我在Where子句得到ArgumentNullException。这里的叠层;
System.ArgumentNullException was unhandled
Message=Value cannot be null.
Parameter name: disposable
Source=System.Reactive
ParamName=disposable
StackTrace:
at System.Collections.Generic.AnonymousObservable`1.Disposable.Set(IDisposable disposable)
at System.Collections.Generic.AnonymousObservable`1.<>c__DisplayClass1.<Subscribe>b__0()
at System.Threading.Scheduler.NowScheduler.Schedule(Action action)
at System.Collections.Generic.AnonymousObservable`1.Subscribe(IObserver`1 observer)
at ConsoleApplication1.Program.Main(String[] args) in C:\Users\Jason\documents\visual studio 2010\Projects\ConsoleApplication1\ConsoleApplication1\Program.cs:line 18
at System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[] args)
at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()
InnerException:
解决方案
此线似乎导致忙乱:
return observer as IDisposable;
您不应该假设观察者是一次性的,你应该返回知道一次性对象“退订”。
该方法返回到基准 IDisposable接口。这使 观察者退订(即 以停止接收通知) 之前,供应商已完成 派他们叫了 订户的OnCompleted方法。
您可以把它用做类似工作:
public class MessageChannel: IObservable<MyMessage>
{
class Subscription : IDisposable {
MessageChannel _c;
IObservable<MyMessage> _obs;
public Subscription(MessageChannel c, IObservable<MyMessage> obs) {
_c = c; _obs = obs;
}
public void Dispose() {
_c.Unsubscribe(_obs);
}
}
public IDisposable Subscribe(IObserver<MyMessage> observer)
{
observers.Add(observer);
return new Subscription(this, observer);
}
void Unsubscribe(IObservable<MyMessage> obs) {
observers.Remove(obs);
}
}
其他提示
<强> !!红旗!! 强>
我强烈建议您不要执行IObserver<T>
或IObservable<T>
自己。赞成使用Observable.Create<T>
或作为最后手段使用Subject
类型。有很多你需要考虑要正确实现这些接口是由正确的Rx类型和运算符为你处理事情。
在这个例子中我将敦促用户删除该MessageChannel类型和交换它
class Program
{
static void Main(string[] args)
{
var channel = GenerateMsgs()
.Where(m => m.process)
.Subscribe((MyMessage m) => Console.WriteLine(m.subject));
}
public IObservable<MyMessage> GenerateMsgs()
{
return Observable.Create<MyMessage>(observer=>
{
observer.OnNext(new MyMessage() {subject = "Hello!", process = true});
});
}
}
public class MyMessage
{
public string subject;
public bool process;
}
在一个系统设计的进一步的检查可能有某种暴露“通道”作为观察序列服务。
public interface OrderService
{
IObservable<OrderRequest> OrderRequests();
IObservable<Order> ProcessedOrders();
IObservable<OrderRejection> OrdersRejections();
}
因此否定了IObserver<T>
或IObservable<T>
的这些自定义实现的需要。
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