如何防止运行多次扫描？

Question

例如

var subject = new Subject<int>();
var test = subject.Scan(0, (x, y) => {
    Console.WriteLine("scan");
    return x + 1;
});
test.Subscribe(x => Console.WriteLine("subscribe1"));
//test.Subscribe(x => Console.WriteLine("subscribe2"));
Observable.Range(0, 1).Subscribe(subject);
Console.WriteLine("done");
Console.Read();

输出为

scan
subscribe1
done

但是如果你取消注释第二个订阅输出是

scan
subscribe1
scan
subscribe2
done

为什么扫描运行两次，我该如何预防？所以输出应该是

scan
subscribe1
subscribe2
done

我使用 Subject 来积累不同的 Observables。然后我使用 Scan 方法更新模型，然后我在不同的地方需要订阅模型更新。也许不使用 Subject 有更好的解决方案？

Answer 1

您看到的问题是 Subject 是一个热可观察对象，而 Scan 会在您每次订阅它时创建一个新的冷可观察对象。

尝试在主题之前移动扫描

var subject = new Subject<int>();
subject.Subscribe(x => Console.WriteLine("subscribe1"));
subject.Subscribe(x => Console.WriteLine("subscribe2"));
Observable.Range(0, 1).Scan(0, (x, y) => {
    Console.WriteLine("scan");
    return x + 1;
}).Subscribe(subject);
Console.WriteLine("done");
Console.Read();

你也可以不用 Subject:

var test = Observable.Range(0, 1).Scan(0, (x, y) => {
    Console.WriteLine("scan");
    return x + 1;
}).Publish();

test.Subscribe(x => Console.WriteLine("subscribe1"));
test.Subscribe(x => Console.WriteLine("subscribe2"));
test.Connect();

Console.WriteLine("done");
Console.Read();

Hot vs Cold Observables

Answer 2

尝试使用 Observable.Publish 获得 IConnectableObservable<T>。

var subject = new Subject<int>();
var test = subject
    .Scan(0, (x, y) => {
        Console.WriteLine("scan");
        return x + 1;
    })
    .Publish();
test.Subscribe(x => Console.WriteLine("subscribe1"));
test.Subscribe(x => Console.WriteLine("subscribe2"));
test.Connect();
Observable.Range(0, 1).Subscribe(subject);
Console.WriteLine("done");
Console.Read();

输出：

scan
subscribe1
subscribe2
done

Publish 将冷的 Scan observable 变成热的 observable，当调用 Connect 时开始发射值。

如何防止运行多次扫描？

How to prevent Scan from running multiple times?

.net

reactive-programming

system.reactive

如何防止 运行 多次扫描？

How to prevent Scan from running multiple times?

.net

reactive-programming

system.reactive

如何防止运行多次扫描？