C# Silverlight：如何使用Webclient异步模式将数据从请求传递到响应？

如何在proxy_OpenReadCompleted方法中访问VIP

void method1() 
{ 
    String VIP = "test";
    WebClient proxy = new WebClient();
    proxy.OpenReadCompleted += new OpenReadCompletedEventHandler(proxy_OpenReadCompleted);
    String urlStr = "someurl/lookup?q=" + keyEntityName + "&fme=1&edo=1&edi=1";
}

void proxy_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
{ 

}

---

这有两种方法。第一个是将字符串作为第二个参数传递到

OpenReadAsync

调用中，此参数成为事件args的

UserState

属性的值

void method1() 
{ 
    String VIP = "test";
    WebClient proxy = new WebClient();
    proxy.OpenReadCompleted += proxy_OpenReadCompleted;
    String urlStr = "someurl/lookup?q=" + keyEntityName + "&fme=1&edo=1&edi=1";
    proxy.OpenReadAsync(new Uri(urlStr, UriKind.Relative), VIP);
}    

void proxy_OpenReadCompleted(object sender, OpenReadCompletedEventArgs e)
{ 
   String VIP = (string)e.UserState;
   // Do stuff that uses VIP.
}

另一种方法是使用闭包直接访问变量：-

void method1() 
{ 
    String VIP = "test";
    WebClient proxy = new WebClient();
    proxy.OpenReadCompleted += (s, args) =>
    {
         // Do stuff that uses VIP.
    }
    String urlStr = "someurl/lookup?q=" + keyEntityName + "&fme=1&edo=1&edi=1";
    proxy.OpenReadAsync(new Uri(urlStr, UriKind.Relative), VIP);
}    

---

请注意，如果异步回调方法写入数据绑定变量，则可能会出现跨线程异常。您需要使用BeginInvoke（）返回UI线程。下面是一个使用WCF服务的示例，但原理是相同的

public void examsCallback(IAsyncResult result)
{
    try
    {
        EntityList<ExamEntity> examList = ((IExamService) result.AsyncState).EndGetAllExams(result);
        Deployment.Current.Dispatcher.BeginInvoke(() =>
        {
            foreach (ExamEntity exam in examList)
            {
                Exams.Add(exam);
            }
            ItemCount = Exams.Count;
            TotalItemCount = Exams.ItemCount;
        });
    }
    catch (Exception ex)
    {
        ErrorHandler.Handle(ex);
    }
}

public void examCallback（IAsyncResult结果）
{
尝试
{
EntityList examList=（（IExamService）result.AsyncState）.EndGetAllExams（result）；
Deployment.Current.Dispatcher.BeginInvoke（（）=>
{
foreach（examList中的考试）
{
考试。添加（考试）；
}
ItemCount=考试数；
TotalItemCount=examies.ItemCount；
});
}
捕获（例外情况除外）
{
ErrorHandler.Handle（ex）；
}
}

public void examsCallback(IAsyncResult result)
{
    try
    {
        EntityList<ExamEntity> examList = ((IExamService) result.AsyncState).EndGetAllExams(result);
        Deployment.Current.Dispatcher.BeginInvoke(() =>
        {
            foreach (ExamEntity exam in examList)
            {
                Exams.Add(exam);
            }
            ItemCount = Exams.Count;
            TotalItemCount = Exams.ItemCount;
        });
    }
    catch (Exception ex)
    {
        ErrorHandler.Handle(ex);
    }
}