C# 如果第一个IObservable为空,则切换到其他IObservable
我正在编写一个函数,用于检索有关主题的新闻,并通过IObservable返回值反馈该新闻 然而,我有几个新闻来源。我不想使用C# 如果第一个IObservable为空,则切换到其他IObservable,c#,.net,system.reactive,C#,.net,System.reactive,我正在编写一个函数,用于检索有关主题的新闻,并通过IObservable返回值反馈该新闻 然而,我有几个新闻来源。我不想使用Merge将这些源合并为一个。相反,我想做的是按优先级排序-- 调用my函数时,将查询第一个新闻源(这将生成表示该源的IObservable) 如果该新闻源的IObservable完成而未返回任何结果,则会查询下一个新闻源 如果第二个消息源完成而没有返回结果,则查询最终的新闻源 这整个行为被包装成一个可观察的我可以返回给用户 这种行为是使用内置Rx扩展方法可以实现的,还是需
Merge
将这些源合并为一个。相反,我想做的是按优先级排序--
///返回第一个序列的元素,如果第一个序列为空,则返回第二个序列中的值。
///第一个序列。
///第二个序列。
///序列中元素的类型。
///顺序。
公共静态IObservable DefaultIfEmpty(此IObservable第一个,IObservable第二个)
{
var signal=new AsyncSubject();
var source1=first.Do(item=>{signal.OnNext(Unit.Default);signal.OnCompleted();});
var source2=第二个.TakeUntil(信号);
返回source1.Concat(source2);//如果source2是冷的,则在source1完成之前不会调用它
}
原来的答案是:
这可能会奏效
var signal1 = new AsyncSubject<Unit>();
var signal2 = new AsyncSubject<Unit>();
var source1 = a.Do(item => { signal1.onNext(Unit.Default); signal1.onCompleted(); });
var source2 = b.Do(item => { signal2.onNext(Unit.Default); signal2.onCompleted(); })).TakeUntil(signal1);
var source3 = c.TakeUntil(signal2.Merge(signal1));
return Observable.Concat(source1, source2, source3);
var signal1=new AsyncSubject();
var signal2=新的AsyncSubject();
var source1=a.Do(item=>{signal1.onNext(Unit.Default);signal1.onCompleted();});
var source2=b.Do(item=>{signal2.onNext(Unit.Default);signal2.onCompleted();})).TakeUntil(signal1);
var source3=c.TakeUntil(signal2.Merge(signal1));
返回Observable.Concat(source1、source2、source3);
编辑:哎呀,第二个信号源需要一个单独的信号,第三个信号源不需要任何信号。
编辑2:哎呀……类型。我习惯了RxJs:)
另外,RX-y的方式也较少,这可能是因为打字少了一点:
var gotResult = false;
var source1 = a();
var source2 = Observable.Defer(() => return gotResult ? Observable.Empty<T>() : b());
var source3 = Observable.Defer(() => return gotResult ? Observable.Empty<T>() : c());
return Observable.Concat(source1, source2, source3).Do(_ => gotResult = true;);
var gotResult=false;
var source1=a();
var source2=Observable.Defer(()=>return-gotResult?Observable.Empty():b());
var source3=Observable.Defer(()=>return-gotResult?Observable.Empty():c());
返回Observable.Concat(source1,source2,source3).Do(=>gotreult=true;);
听起来您可以使用普通的Amb
查询
编辑:根据评论,Amb
不会这样做-对其进行重击:
public static IObservable<T> SwitchIfEmpty<T>(
this IObservable<T> first,
Func<IObservable<T>> second)
{
return first.IsEmpty().FirstOrDefault() ? second() : first;
}
编辑:
我想你也可以把它概括为:
public static IObservable<T> SwitchIf<T>(
this IObservable<T> first,
Func<IObservable<T>, IObservable<bool>> predicate,
Func<IObservable<T>> second)
{
return predicate(first).FirstOrDefault()
? second()
: first;
}
公共静态IObservable开关IF(
首先,这是可以观察到的,
Func谓词,
(第二)
{
返回谓词(first).FirstOrDefault()
?第二()
:第一;
}
另一种方法-与其他方法相比差异相当大,因此我将提出一个新的答案:
下面是各种有趣的调试行:
public static IObservable<T> FirstWithValues<T>(this IEnumerable<IObservable<T>> sources)
{
return Observable.Create<T>(obs =>
{
// these are neat - if you set it's .Disposable field, and it already
// had one in there, it'll auto-dispose it
SerialDisposable disp = new SerialDisposable();
// this will trigger our exit condition
bool hadValues = false;
// start on the first source (assumed to be in order of importance)
var sourceWalker = sources.GetEnumerator();
sourceWalker.MoveNext();
IObserver<T> checker = null;
checker = Observer.Create<T>(v =>
{
// Hey, we got a value - pass to the "real" observer and note we
// got values on the current source
Console.WriteLine("Got value on source:" + v.ToString());
hadValues = true;
obs.OnNext(v);
},
ex => {
// pass any errors immediately back to the real observer
Console.WriteLine("Error on source, passing to observer");
obs.OnError(ex);
},
() => {
// A source completed; if it generated any values, we're done;
if(hadValues)
{
Console.WriteLine("Source completed, had values, so ending");
obs.OnCompleted();
}
// Otherwise, we need to check the next source in line...
else
{
Console.WriteLine("Source completed, no values, so moving to next source");
sourceWalker.MoveNext();
disp.Disposable = sourceWalker.Current.Subscribe(checker);
}
});
// kick it off by subscribing our..."walker?" to the first source
disp.Disposable = sourceWalker.Current.Subscribe(checker);
return disp.Disposable;
});
}
输出:
Source A invoked
Got value on source:Article from A
Article from A
Source completed, had values, so ending
Source A invoked
Source completed, no values, so moving to next source
Source B invoked
Got value on source:Article from B
Article from B
Source completed, had values, so ending
Source A invoked
Source completed, no values, so moving to next source
Source B invoked
Source completed, no values, so moving to next source
Source C invoked
Got value on source:Article from C
Article from C
Source completed, had values, so ending
在我看来,接受的答案是不可取的,因为它使用了
Subject
,Do
,并且在第一个序列不是空的情况下仍然订阅第二个序列。如果第二个可观察对象调用任何非平凡的东西,那么后者可能是一个大问题。我提出了以下解决方案:
public static IObservable<T> SwitchIfEmpty<T>(this IObservable<T> @this, IObservable<T> switchTo)
{
if (@this == null) throw new ArgumentNullException(nameof(@this));
if (switchTo == null) throw new ArgumentNullException(nameof(switchTo));
return Observable.Create<T>(obs =>
{
var source = @this.Replay(1);
var switched = source.Any().SelectMany(any => any ? Observable.Empty<T>() : switchTo);
return new CompositeDisposable(source.Concat(switched).Subscribe(obs), source.Connect());
});
}
public static IObservable SwitchIfEmpty(this IObservable@this,IObservable switchTo)
{
如果(@this==null)抛出新的ArgumentNullException(nameof(@this));
如果(switchTo==null)抛出新的ArgumentNullException(nameof(switchTo));
返回可观察的。创建(obs=>
{
var source=@this.Replay(1);
var switched=source.Any().SelectMany(Any=>Any?Observable.Empty():switcheto);
返回新的CompositeDisposable(source.Concat(switched.Subscribe(obs),source.Connect());
});
}
名称SwitchIfEmpty
与。是关于将一些RxJava操作符合并到RxNET中的持续讨论
我确信一个定制的
IObservable
实现将比我的实现更高效。您可以找到一个由ReactiveX成员编写的。它也可以在上找到。这里是JerKimball运算符的非阻塞版本
/// <summary>Returns the elements of the first sequence, or the elements of the
/// second sequence if the first sequence is empty.</summary>
public static IObservable<T> SwitchIfEmpty<T>(this IObservable<T> first,
IObservable<T> second)
{
return Observable.Defer(() =>
{
bool isEmpty = true;
return first
.Do(_ => isEmpty = false)
.Concat(Observable.If(() => isEmpty, second));
});
}
///返回第一个序列的元素或
///如果第一个序列为空,则为第二个序列。
公共静态IObservable SwitchIfEmpty(此IObservable优先,
IObservable(秒)
{
返回可观察的延迟(()=>
{
bool isEmpty=true;
先返回
.Do(=>isEmpty=false)
.Concat(可观察。如果(()=>为空,则为秒));
});
}
这是同一个操作符的一个版本,它接受多个序列,并返回第一个非空序列的元素:
/// <summary>Returns the elements of the first non-empty sequence.</summary>
public static IObservable<T> SwitchIfEmpty<T>(params IObservable<T>[] sequences)
{
return Observable.Defer(() =>
{
bool isEmpty = true;
return sequences
.Select(s => s.Do(_ => isEmpty = false))
.Select(s => Observable.If(() => isEmpty, s))
.Concat();
});
}
///返回第一个非空序列的元素。
公共静态IObservable SwitchIfEmpty(参数IObservable[]序列)
{
返回可观察的延迟(()=>
{
bool isEmpty=true;
返回序列
.Select(s=>s.Do(=>isEmpty=false))
.选择(s=>Observable.If(()=>isEmpty,s))
.Concat();
});
}
Observable.Defer
操作符用于防止多个订阅共享相同的bool isEmpty
状态(有关此操作的更多信息).如果您能帮助我重新编写这个问题,我也将不胜感激——我已经尽了最大的努力,但这个问题很难用语言表达出来。如果源A返回结果,然后完成,会发生什么?转到来源B?还有,“新闻查询者”电话的签名是什么?它是否已经返回IObservable
?@JerKimball如果A返回结果,我们不关心abo
Source A invoked
Got value on source:Article from A
Article from A
Source completed, had values, so ending
Source A invoked
Source completed, no values, so moving to next source
Source B invoked
Got value on source:Article from B
Article from B
Source completed, had values, so ending
Source A invoked
Source completed, no values, so moving to next source
Source B invoked
Source completed, no values, so moving to next source
Source C invoked
Got value on source:Article from C
Article from C
Source completed, had values, so ending
public static IObservable<T> SwitchIfEmpty<T>(this IObservable<T> @this, IObservable<T> switchTo)
{
if (@this == null) throw new ArgumentNullException(nameof(@this));
if (switchTo == null) throw new ArgumentNullException(nameof(switchTo));
return Observable.Create<T>(obs =>
{
var source = @this.Replay(1);
var switched = source.Any().SelectMany(any => any ? Observable.Empty<T>() : switchTo);
return new CompositeDisposable(source.Concat(switched).Subscribe(obs), source.Connect());
});
}
/// <summary>Returns the elements of the first sequence, or the elements of the
/// second sequence if the first sequence is empty.</summary>
public static IObservable<T> SwitchIfEmpty<T>(this IObservable<T> first,
IObservable<T> second)
{
return Observable.Defer(() =>
{
bool isEmpty = true;
return first
.Do(_ => isEmpty = false)
.Concat(Observable.If(() => isEmpty, second));
});
}
/// <summary>Returns the elements of the first non-empty sequence.</summary>
public static IObservable<T> SwitchIfEmpty<T>(params IObservable<T>[] sequences)
{
return Observable.Defer(() =>
{
bool isEmpty = true;
return sequences
.Select(s => s.Do(_ => isEmpty = false))
.Select(s => Observable.If(() => isEmpty, s))
.Concat();
});
}