Silverlight：如何在異步HttpWebRequest完成時更新UI？

Question

我寫的輔助類來檢索Web服務數據在Silverlight中使用：

public static class RequestMethod 
{ 
    public static string Get = "GET"; 
    public static string Post = "POST"; 


} 
public static class RequestDataType 
{ 
    public static string Xml = "Xml"; 
    public static string Json = "application/json"; 
} 
public class HttpWebRequestHelper<T> 
{ 

    private readonly SynchronizationContext _context; 


    private readonly ObservableCollection<T> _collection = 
      new ObservableCollection<T>(); 
    public ObservableCollection<T> Collection 
    { 
     get { return _collection; } 
    } 

    public HttpWebRequestHelper() 
    { 
     _context = SynchronizationContext.Current; 
    } 

    public ObservableCollection<T> GetCollection() 
    { 
     if (HttpWebRequest == null) throw new ArgumentNullException("request"); 
     HttpWebRequest.BeginGetResponse((result) => 
     { 
      var response = HttpWebRequest.EndGetResponse(result); 
      var stream = response.GetResponseStream(); 
      if (stream == null) return; 
      var reader = new StreamReader(stream, Encoding.UTF8); 
      var responseString = reader.ReadToEnd(); 
    var desirilizedObject = JsonConvert.DeserializeObject<IEnumerable<T>>(responseString); 
      _context.Post((state) => 
           { 
            Collection.Clear(); 
            foreach (var item in desirilizedObject) 
            { 
             Collection.Add(item); 
            } 
           }, null); 
     }, null); 
     return Collection; 
    } 

    private HttpWebRequest HttpWebRequest { get; set; } 
    public void CreateRequest (string url,string requestMethod, string requestDataType) 
    { 

     var uri = new Uri(url, UriKind.Absolute); 
     var request = (HttpWebRequest)WebRequest.Create(uri); 
     request.Method = requestMethod; 
     request.Accept = requestDataType; 
     HttpWebRequest= request; 
    } 


} 

這是我班的樣本用法：

var request = new HttpWebRequestHelper<DriverModel>(); 
     request.CreateRequest("http://localhost:11624/api/Drivers/", RequestMethod.Get, RequestDataType.Json); 
     request.GetCollection(); 
     this.DataContext = request; 

我想更新UI HttpWebRequest的完成時。 我該怎麼做？

Answer 1

我想當你的請求完成後，你會得到錯誤改變UI元素。如果是這種情況，你應該加入到當前的線程中;

Deployment.Current.Dispatcher.BeginInvoke(() => { this.Visibility = Visibility.Collapsed; });