C#中的参数超出范围异常错误

Question

我的方法是这样的。 (Grabbed from here)

private void inetConvert() {
    byte[] buf = new byte[1024];
    string result;
    string xeString = String.Format("http://www.xe.com/ucc/convert.cgi?Amount=1&From={0}&To={1}", srcCurrency, dstCurrency);
    System.Net.WebRequest wreq = System.Net.WebRequest.Create(new Uri(xeString));
    System.Net.WebResponse wresp = wreq.GetResponse();
    Stream respstr = wresp.GetResponseStream();
    int read = respstr.Read(buf, 0, 10240); // Error
    result = Encoding.ASCII.GetString(buf, 0, read); 
    curRateLbl.Text= result;
}

问题是，当应用程序执行这个应用程序在挂起大约 4-5 秒后得到这个屏幕

我错过了什么？

Answer 1

缓冲区的大小是 1024，但您告诉 Read 它最多可以将 10240（大小的十倍）字节放入缓冲区。如文件所述，它抛出是因为

偏移量和计数之和大于缓冲区长度。

Answer 2

最后你有一个额外的 0。应该是

  int read = respstr.Read(buf, 0, 1024); // Error 

这就是您在应用程序中使用常量的原因，以避免那些胖乎乎的手指错误。

private void inetConvert() {  
    private const BUFFER_SIZE = 1024;
    byte[] buf = new byte[BUFFER_SIZE];  
    string result;  
    string xeString = String.Format("http://www.xe.com/ucc/convert.cgi?Amount=1&From={0}&To={1}", srcCurrency, dstCurrency);  
    System.Net.WebRequest wreq = System.Net.WebRequest.Create(new Uri(xeString));  

    // VERY IMPORTANT TO CLEAN UP RESOURCES FROM ANY OBJECT THAT IMPLEMENTS IDisposable

    using(System.Net.WebResponse wresp = wreq.GetResponse()) 
    using(Stream respstr = wresp.GetResponseStream())
    {
      int read = respstr.Read(buf, 0, BUFFER_SIZE); // Error  
      result = Encoding.ASCII.GetString(buf, 0, read);   
      curRateLbl.Text= result;  
    }
}  

另请注意，您没有正确关闭 Stream 对象。您可能会考虑使用 using 语句来帮助管理流中的资源。

但是...我会这样做。

private void inetConvert() 
{   
    string xeString= String.Format("http://www.xe.com/ucc/convert.cgi?Amount=1&From={0}&To={1}", srcCurrency, dstCurrency);  

    System.Net.WebRequest wreq = System.Net.WebRequest.Create(new Uri(xeString));  

    // VERY IMPORTANT TO CLEAN UP RESOURCES FROM ANY OBJECT THAT IMPLEMENTS IDisposable

    using(System.Net.WebResponse wresp = wreq.GetResponse()) 
    using (Stream stream = response.GetResponseStream()) 
    { 
        StreamReader reader = new StreamReader(stream, Encoding.UTF8); 
        curRateLbl.Text = reader.ReadToEnd(); 
    } 
}