C＃中的参数超出范围异常错误＃

Question

我的方法看起来像这样。 (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; 
} 

的问题是，当应用程序执行这个应用程序挂约4-5秒

我错过之后得到这个屏幕？

Answer 1

缓冲区的大小是1024，但是你告诉Read它可以将10240（十倍大小）字节放入缓冲区。如文档所述，它会抛出，因为

偏移量和计数的总和大于缓冲区长度。

Answer 2

你在最后有一个额外的0。应该是

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

这就是为什么你在你的应用中使用常量，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。您可以考虑使用using语句来帮助管理流中的资源。

但是...这是我将如何做到这一点。

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(); 
    } 
}