跨域访问策略文件在silverlight2 beta2中的变化

今天将silverlight2 beta1的程序转换成silverlight2 beta2的程序后，发现以前的wcf无法正常调用，vs.net2008 的提示如下：
"An exception of type 'System.ServiceModel.ProtocolException' occurred in System.ServiceModel.dll but was not handled in user code
Additional information: The remote server returned an unexpected response: (404) Not Found."
当直接在网页中输入.svc文件的连接地址的时候发现服务是可用的，于是怀疑是客户端跨域访问策略文件（clientaccesspolicy.xml ）产生的问题，查了下资料，原来是在beta2版本中，策略文件的写法有所改变

Cross-domain restrictions still apply within beta 2 and the same rules apply.  There is one subtle change that is required to your clientaccesspolicy.xml file that is required.  In the allow-from node of the policy file, the attribute http-request-headers is now required.  If your service is an open/public one then specifying “*” is probably acceptable (you’ll have to be the judge of that.  If you only wanted to allow specific headers (besides the blacklisted ones) you can provide those in a comma-separated list and can use wildcards as well.  For example you could use X-MyApp-* if you wanted.

Another thing to note about the support for Adobe’s crossdomain.xml policy file is one thing we found in interpretation of the policy template.  Previously Flash was a Macromedia product and as such that file is adorned with a DOCTYPE that represents a schema with macromedia in it.  Well, Adobe has changed the schema a little bit and also updated the DOCTYPE to reflect Adobe as the authority.  Right now, Silverlight still expects to validate the macromedia declaration.

于是将clientaccesspolicy.xml 的内容修改成如下

<?xml version="1.0" encoding="utf-8"?>
<access-policy>
  <cross-domain-access>
    <policy>
      <allow-from http-request-headers="*">
        <domain uri="*"/>
      </allow-from>
      <grant-to>
        <resource path="/" include-subpaths="true"/>
      </grant-to>
    </policy>
  </cross-domain-access>
</access-policy>

保存修改，重新编译了一下wcf service，在silverlight 的客户端程序中更新对wcf service的引用，运行成功