Observable和Webclient获取CSV csv

Question

我在我的lightswitch应用程序中有一个函数，该函数从一个站点下载一个csv文件，我希望使用Rx框架重新编写这个文件并提供同步调用它的可能性。

以下提供了旧功能和新功能的代码片段。然而，新功能不起作用，对ParseCSV的调用从不发生。我想知道为什么，如果存在更好的解决方案，随时提供。

旧代码：

private void ObservableCollection<Data> collection; 
public ObservableCollection<Data> GetData(string url, ObservableCollection<Data> targetCollection) 
{ 

collection = targetCollection; 
if (!string.IsNullOrEmpty(url)) 
{ 
    WebClient wc = new WebClient(); 
    wc.OpenReadCompleted += new OpenReadCompletedEventHandler(OpenReadCompleted_ParseCSV); 
    wc.OpenReadAsync(new Uri(url)); 
} 
return collection; 
} 

private void OpenReadCompleted_ParseCSV(object sender, OpenReadCompletedEventArgs e) 
{ 

if (e.Error != null) return; 

var webClient = sender as WebClient; 
if (webClient == null) return; 

try 
{ 
    using (StreamReader reader = new StreamReader(e.Result)) 
    { 
     string contents = reader.ReadToEnd(); 
     ... 
    } 
} 
catch (Exception ex) 
{ 
    System.Diagnostics.Debug.WriteLine("Error parsing CSV!\n" + ex.Message); 
} 

}

新代码（其中Rx）：

private void ObservableCollection<Data> collection; 
public ObservableCollection<Data> GetData(string url, ObservableCollection<Data> targetCollection) 
{ 
collection = targetCollection; 
if (!string.IsNullOrEmpty(url)) 
{ 
    var result = Observable.FromEventPattern<OpenReadCompletedEventHandler, OpenReadCompletedEventArgs> 
       (
        ev => webClient.OpenReadCompleted += ev, 
        ev => webClient.OpenReadCompleted -= ev 
       ) 
       .Select(o => o.EventArgs.Result) 
       .FirstOrDefault() 
       .ParseCSV(); 

    // Call the Async method 
    webClient.OpenReadAsync(new Uri(url)); 
} 
return collection; 
} 

private void ParseCSV(this Stream stream) 
{ 
try 
{ 
    using (StreamReader reader = new StreamReader(e.Result)) 
    { 
     string contents = reader.ReadToEnd(); 
     ... 
    } 
} 
catch (Exception ex) 
{ 
    System.Diagnostics.Debug.WriteLine("Unable to get history data!\n" + ex.Message); 
} 
} 

Answer 1

这很难知道你要什么（我想你试图贬低在StackOverflow上发布的代码，并且在翻译中丢失了很多），但我认为几乎没有我会改变这一点。

我注意到的一件事是，你在主线程上解析结果。还有，你可以这样做的原因，但你可能会考虑这一点：

//Note the void here. Is your intention to return a new collection or contribute 
//to an existing one? I assumed the latter and changed the method to be more clear 
//that this method causes side effects. 
public void GetData(string url, ObservableCollection<Data> targetCollection) 
{ 
     var result = Observable 
      .FromEventPattern<OpenReadCompletedEventHandler, OpenReadCompletedEventArgs> 
      (
       ev => webClient.OpenReadCompleted += ev, 
       ev => webClient.OpenReadCompleted -= ev 
      ) 
      .Select(o => ParseCSV(o.EventArgs.Result)); 

    result.Subscribe(targetCollection.Add); 
    webClient.OpenReadAsync(new Uri(url)); 
} 

//This method now returns a Data object read from a Stream 
private static Data ParseCSV(Stream stream) 
{ 
    try 
    { 
     using (StreamReader reader = new StreamReader(stream)) 
     { 
      string contents = reader.ReadToEnd(); 
      //... 
      return data; 
     } 
    } 
    catch (Exception ex) 
    { 
     //Use Exception.ToString(). You get error and stack trace information 
     //For this error as well as any inner exceptions. Nice! 
     System.Diagnostics.Debug.WriteLine("Unable to get history data!\n" + ex.ToString()); 
    } 
    return null; 
} 

这里，对于回来从Web客户端请求（将只有一个），每个值，我们突出结果到您的Data类，而不是在可观察流之外进行转换。

我对你的方法做了一些小的修改。我并不特别喜欢这种副作用的代码（通过集合来贡献似乎是一个错误的向量），但我会允许它。除此之外，我认为这应该工作得很好。

Answer 2

一种用于WPF

改进回答创建一个新的项目，并在你的主窗口粘贴此代码。添加一个名为XBStart的按钮，如果您将点击处理程序连接到XBStart_Click，则您将全部设置。运行该项目并单击按钮！

public partial class MainWindow : Window 
{ 
    public MainWindow() 
    { 
     InitializeComponent(); 
     RX.DataReady += new RX.OnData(RX_DataReady); 
    } 

    private void RX_DataReady(ObservableCollection<string> Data) 
    { 
     Debugger.Break(); 
    } 

    private void XBStart_Click(object sender, RoutedEventArgs e) 
    { 
     RX.GetData("http://www.yahoo.com"); 
    } 
} 

public static class RX 
{ 
    public delegate void OnData(ObservableCollection<string> Data); 

    public static event OnData DataReady; 

    private static WebClient webClient; 

    private static ObservableCollection<string> TheData { get; set; } 

    private static void Notify() 
    { 
     if (DataReady != null) 
     { 
      DataReady(TheData); 
     } 
    } 

    public static void GetData(string url) 
    { 
     webClient = new WebClient(); 
     TheData = new ObservableCollection<string>(); 
     var result = Observable 
      .FromEventPattern<OpenReadCompletedEventHandler, 
           OpenReadCompletedEventArgs> 
      (
       ev => webClient.OpenReadCompleted += ev, 
       ev => webClient.OpenReadCompleted -= ev 
      ) 
      .Select(o => Parse.CSV(o.EventArgs.Result)); 

     result.Subscribe<string>(p => 
     { 
      TheData.Add(p); 
      Notify(); 
     }); 
     webClient.OpenReadAsync(new Uri(url)); 
    } 
} 

public static class Parse 
{ 
    //This method now returns a Data object read from a Stream 
    public static string CSV(Stream stream) 
    { 
     try 
     { 
      using (StreamReader reader = new StreamReader(stream)) 
      { 
       string contents = reader.ReadToEnd(); 
       //... 
       return contents; 
      } 
     } 
     catch (Exception ex) 
     { 
      //Use Exception.ToString(). 
      //You get error and stack trace information 
      //For this error as well as any inner exceptions. Nice! 
      System.Diagnostics.Debug.WriteLine("Unable to get history data!\n" + 
               ex.ToString()); 
     } 
     return null; 
    } 
}