简单的 Rx 示例要么阻塞要么有竞争条件

Question

观看后：Intro to Reactive Programming我正在尝试使用 C# 和reactiveX 复制示例。总之，它是一个货币转换器。用户指定他们想要的货币数量和类型。当前汇率是从服务器检索的，返回所需的时间不定。由于这个可变的服务器时间，旧的货币请求可能会在最近的请求之后进入。这个警告被用作使事情具有反应性以避免竞争条件错误的动机。我可以通过在代表货币汇率的任务上使用 Wait() 来避免我的反应代码中的竞争条件，但这会阻止 GUI。我应该如何接近这个？也许我应该取消其他任务？下面是我的代码，它不会阻塞但存在竞争条件问题。

public CurrencyWindow()

{

    InitializeComponent();

    var amount = Observable.FromEventPattern<TextChangedEventArgs>(

        txtAmount, "TextChanged").Select(t=>int.Parse(txtAmount.Text));

    var yen = Observable.FromEventPattern<RoutedEventArgs>(

        rdoYen, "Checked").Select(t => "Yen");

    var dollar = Observable.FromEventPattern<RoutedEventArgs>(

        rdoDollar, "Checked").Select(t => "Dollar");

    var pound = Observable.FromEventPattern<RoutedEventArgs>(

        rdoPound, "Checked").Select(t => "Pound");

    // merge the currency selection into one stream.

    var currencyType = yen.Merge(dollar).Merge(pound);

    // Lets now get a stream of currency rates.

    var exchangeRate = currencyType.Select(s => GetExchangeRate(s));

    amount.CombineLatest(exchangeRate, async (i, d) => i * await d).Subscribe(async v =>

    {

        var val = await v;

        txtCost.Text = val.ToString();

    });

}

private Task<double> GetExchangeRate(string currency)

{

    double exchange = 0;

    switch(currency)

    {

        case "Yen":

            exchange = 1;

            break;

        case "Pound":

            exchange = 2;

            break;

        case "Dollar":

            exchange = 3;

            break;

    }

    return Task.Factory.StartNew(() => 

    {

        System.Threading.Thread.Sleep((int)exchange * 3000);

        return exchange;

    });

}

Answer 1

试试这个代码，看看它是否有效：var exchangeRate = currencyType&nbsp; &nbsp; .Select(s => Observable.FromAsync(() => GetExchangeRate(s)))&nbsp; &nbsp; .Switch();amount&nbsp; &nbsp; .CombineLatest(exchangeRate, (i, d) => i * d)&nbsp; &nbsp; .Subscribe(v =>&nbsp; &nbsp; {&nbsp; &nbsp; &nbsp; &nbsp; var val = v;&nbsp; &nbsp; &nbsp; &nbsp; txtCost.Text = val.ToString();&nbsp; &nbsp; });此代码将确保只有最新currencyType生成的才会返回汇率。如果出现了一种新货币，那么所有先前的飞行调用都GetExchangeRate将被忽略（即使它们在当前调用之后出现）。