使用 Task.Factory 返回值以更新 UI

Question

这应该很容易，但我找不到合适的术语来搜索...好吧，我是 C# 新手，我正在尝试制作一个简单的应用程序来编写 web 服务的返回。

我遇到了使用线程的需要...向线程传递参数相当容易，我找不到从 Threaded 方法返回并更新我的 UI 以显示结果的方法（实际上没有现在的实际结果）

事件：

    private void TextBox_TextChanged_1(object sender, TextChangedEventArgs e)
    {
        minhaSigla = Sigla.Text;
        Task.Factory.StartNew(() => GetQuoteAndUpdateText(minhaSigla));
        tb1.Text = "UIElement-TO-UPDATE";

    }

然后是线程方法

    private string GetQuoteAndUpdateText(string sign)
    {
        string SoapEnvelope = "";
        SoapEnvelope = "<?xml version=\"1.0\" encoding=\"utf-8\"?>";
        SoapEnvelope += "<soap:Envelope ";
        SoapEnvelope += "xmlns:xsi = \"http://www.w3.org/2001/XMLSchema-instance\" ";
        SoapEnvelope += "xmlns:xsd= \"http://www.w3.org/2001/XMLSchema\" ";
        SoapEnvelope += "xmlns:soap= \"http://schemas.xmlsoap.org/soap/envelope/\">";
        SoapEnvelope += "<soap:Body>";
        SoapEnvelope += "   <GetQuote xmlns=\"http://www.webserviceX.NET/\"> ";
        SoapEnvelope += "       <symbol>" + sign + "</symbol> ";
        SoapEnvelope += "   </GetQuote> ";
        SoapEnvelope += "</soap:Body>";
        SoapEnvelope += "</soap:Envelope>";

        EndpointAddress endpoint = new EndpointAddress("http://www.webservicex.net/stockquote.asmx");
        BasicHttpBinding basicbinding = new BasicHttpBinding();
        basicbinding.SendTimeout = new TimeSpan(3000000000);
        basicbinding.OpenTimeout = new TimeSpan(3000000000);

        stockbyname.StockQuoteSoapClient sbn = new stockbyname.StockQuoteSoapClient(basicbinding, endpoint);

        XmlDocument xmlDocument = new XmlDocument();
        return sbn.GetQuote(SoapEnvelope);
    }

任何信息都将不胜感激，甚至是关于我的代码有多糟糕的信息：P

Answer 1

无需深入了解async/await 的所有乐趣，您可以使用Task 的ContinueWith 方法来处理返回的信息。

private void TextBox_TextChanged_1(object sender, TextChangedEventArgs e)
{
    minhaSigla = Sigla.Text;
    var quoteGetterTask = Task.Factory.StartNew(() => GetQuoteAndUpdateText(minhaSigla));
    quoteGetterTask.ContinueWith(task => 
    {
        var theResultOfYourServiceCall = task.Result;
        //You'll need to use a dispatcher here to set the value of the text box (see below)
        tb1.Text = theResultOfYourServiceCall;     //"UIElement-TO-UPDATE";
    });
}

正如我在上面的代码示例中提到的，根据您使用的 UI 技术，您需要使用调度程序来避免出现非法的跨线程访问异常。

.ContinueWith内的表达式的WinForms示例（使用Control的Invoke方法）

task =>
{
    var theResultOfYourServiceCall = task.Result;
    tb1.Invoke(new Action(() => tb1.Text = theResultOfYourServiceCall));
}

.ContinueWith里面的表达式的WPF例子（使用WPF的Dispatcher）

task =>
{
    var theResultOfYourServiceCall = task.Result;
    tb1.Dispatcher.Invoke(DispatcherPriority.Normal, 
                          new Action(() => tb1.Text = theResultOfYourServiceCall));
}

.ContinueWith 内的表达式的 Silverlight/Windows Phone 示例（使用 Silverlight 的 Dispatcher）

task =>
{
    var theResultOfYourServiceCall = task.Result;
    tb1.Dispatcher.BeginInvoke(() => tb1.Text = theResultOfYourServiceCall);
}

.ContinueWith 内表达式的 Windows Store 示例（使用 CoreDispatcher）

task =>
{
    var theResultOfYourServiceCall = task.Result;
    tb1.Dispatcher.RunAsync(CoreDispatcherPriority.Normal, () => tb1.Text = theResultOfYourServiceCall);
}

Answer 2

更常见的是，您需要 UI 线程上的任务，因为这可以让您更新您的控件。

Task<string>.Factory.StartNew(() => GetQuoteAndUpdateText(minhaSigla)).ContinueWith(s=>  tb1.Text = s, 
TaskScheduler.FromCurrentSynchronizationContext());

ps : 你也可以在 .net 4.5 中使用 await & async

Answer 3

其他人提到了async/await，但这里有一个简单的例子：

private async void TextBox_TextChanged_1(object sender, TextChangedEventArgs e)
{
    minhaSigla = Sigla.Text;
    string result = await GetQuoteAndUpdateTextAsync(minhaSigla);
    tb1.Text = "UIElement-TO-UPDATE";
}

private Task<string> GetQuoteAndUpdateTextAsync(string sign)
{
    string SoapEnvelope = "";
    SoapEnvelope = "<?xml version=\"1.0\" encoding=\"utf-8\"?>";
    SoapEnvelope += "<soap:Envelope ";
    SoapEnvelope += "xmlns:xsi = \"http://www.w3.org/2001/XMLSchema-instance\" ";
    SoapEnvelope += "xmlns:xsd= \"http://www.w3.org/2001/XMLSchema\" ";
    SoapEnvelope += "xmlns:soap= \"http://schemas.xmlsoap.org/soap/envelope/\">";
    SoapEnvelope += "<soap:Body>";
    SoapEnvelope += "   <GetQuote xmlns=\"http://www.webserviceX.NET/\"> ";
    SoapEnvelope += "       <symbol>" + sign + "</symbol> ";
    SoapEnvelope += "   </GetQuote> ";
    SoapEnvelope += "</soap:Body>";
    SoapEnvelope += "</soap:Envelope>";

    EndpointAddress endpoint = new EndpointAddress("http://www.webservicex.net/stockquote.asmx");
    BasicHttpBinding basicbinding = new BasicHttpBinding();
    basicbinding.SendTimeout = new TimeSpan(3000000000);
    basicbinding.OpenTimeout = new TimeSpan(3000000000);

    stockbyname.StockQuoteSoapClient sbn = new stockbyname.StockQuoteSoapClient(basicbinding, endpoint);

    XmlDocument xmlDocument = new XmlDocument();
    return sbn.GetQuoteAsync(SoapEnvelope);
}

请注意它与您现有的方法有多么相似。这就是async 的力量。