在Silverlight里面调用WebServices和WCF是一件麻烦的事，在开发的时候，如果IP更改了，总是需要重配或者更新。虽然可以动态绑定，但是IP还是要配吧，而且性能比写死的要慢很多。而且，还得在根目录加上跨域XML。那么有什么解决方案呢？
比如有这么一个需求，当用户选择文件后，需要查询数据库获取是否可上传，以及上传的最大限制。由于以上原因，不愿意使用WebServices或者WCF来获取数据，于是首先想到的是写在initParams参数里面，但是不够理想，如果设置比较多，或者有更多自定义的条件的话，不太好处理。接下来就想到了利用ASP.NET里面的一般处理程序，具体操作如下：
1）在initParams配置参数“UploadHandlerName=Ajax/HttpUploadHandler.ashx”。
2）在Silverlight程序中的添加文件的方法中编写请求代码。这块值得注意的，一是路径，二是获取到数据后，要使用this.Dispatcher.BeginInvoke来更新界面（否则会出异常）。具体代码如下：
public class RequestStates
{
/// <summary>
/// 当前请求
/// </summary>
public HttpWebRequest CurrentWebRequest { get; set; }
/// <summary>
/// 当前用户文件
/// </summary>
public UserFile CurrentUserFile { get; set; }
}
private void AddFile(FileInfo file)
{
string fileName = file.Name;
var userFile = new UserFile { FileName = file.Name, FileStream = file.OpenRead() };
if (!string.IsNullOrEmpty(Configuration.Instance.CheckExtensionsHandlerName))
{
//获取处理的Handler类的路径
UriBuilder httpHandlerUrlBuilder = new UriBuilder(new CustomUri(Configuration.Instance.CheckExtensionsHandlerName));
//设置请求的参数
httpHandlerUrlBuilder.Query = string.Format("{2}file={0}&Extension={1}", HttpUtility.UrlEncode(userFile.FileName), HttpUtility.UrlEncode(Path.GetExtension(userFile.FileName)), string.IsNullOrEmpty(httpHandlerUrlBuilder.Query) ? string.Empty : httpHandlerUrlBuilder.Query.Remove(0, 1) + "&");
//创建请求
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(httpHandlerUrlBuilder.Uri);
request.Method = "POST";
//设置自定义信息，用于异步请求
var requestStates = new RequestStates()
{
CurrentUserFile = userFile,
CurrentWebRequest = request
};
//开始异步请求
request.BeginGetRequestStream(new AsyncCallback(RequestReady), requestStates);
}
else
{
_files.Add(userFile);
}
}
private void RequestReady(IAsyncResult asynchronousResult)
{
var requestStates = (RequestStates)asynchronousResult.AsyncState;
HttpWebRequest webRequest = requestStates.CurrentWebRequest;
Stream requestStream = webRequest.EndGetRequestStream(asynchronousResult);
requestStream.Close();
webRequest.BeginGetResponse(new AsyncCallback(ResponseReady), requestStates);
}
void ResponseReady(IAsyncResult asyncResult)
{
var requestStates = (RequestStates)asyncResult.AsyncState;
HttpWebRequest webRequest = requestStates.CurrentWebRequest;
var userFile = requestStates.CurrentUserFile;
var webResponse = (HttpWebResponse)webRequest.EndGetResponse(asyncResult);
var reader = new StreamReader(webResponse.GetResponseStream());
//获取Httphandler类返回的数据
string responsestring = reader.ReadToEnd();
reader.Close();
decimal maxSize = Convert.ToDecimal(responsestring);
//Check for the file size limit (configurable)
if (maxSize == 0 || (userFile.FileStream.Length / 1024) <= maxSize)
{
this.Dispatcher.BeginInvoke(
() => _files.Add(userFile)
);
}
else if (maxSize < 0)
{
this.Dispatcher.BeginInvoke(
delegate()
{
var messageWindow = new MessageChildWindow
{
Message =
string.Format("不允许上传{0}类文件！",
Path.GetExtension(userFile.FileName))
};
messageWindow.Show();
if (MaximumFileSizeReached != null)
MaximumFileSizeReached(this, null);
});
}
else
{
this.Dispatcher.BeginInvoke(
() =>
{
var messageWindow = new MessageChildWindow
{
Message =
string.Format("{0}{1}{2}KB.",
Path.GetExtension(userFile.FileName),
UserMessages.MaxFileSize, (maxSize).ToString())
};
messageWindow.Show();
if (MaximumFileSizeReached != null)
MaximumFileSizeReached(this, null);
});
}
}
效果如下：
