Web服务：无法将类型'System.Xml.Linq.XElement'隐式转换为'System.Xml.XmlElement'

Question

I have a scenario where i have created a web service, which returns the first name and last name of the username passed through client(webservice consumer).

but im getting an error in 5th line :Cannot implicitly convert type 'System.Xml.Linq.XElement' to 'System.Xml.XmlElement'

Below is the code using to retrieve data

protected void BindUserDetails(string userName)
    {
        UserService.ServiceSoapClient client = new UserService.ServiceSoapClient();
        DataSet dsresult = new DataSet();
       XmlElement exelement = client.GetUserDetails(userName);
        if (exelement != null)
        {
            XmlNodeReader nodereader = new XmlNodeReader(exelement);
            dsresult.ReadXml(nodereader, XmlReadMode.Auto);
            gvUserDetails.DataSource = dsresult;
            gvUserDetails.DataBind();
        }
        else
        {
            gvUserDetails.DataSource = null;
            gvUserDetails.DataBind();
        }
    }

UserService is the Service reference which i have added. gvUserDetails is the gridview

[WebMethod]
    public XmlElement GetUserDetails(string username) {

        SqlConnection cn = new SqlConnection(ConfigurationManager.ConnectionStrings["TestingCS"].ConnectionString);
        cn.Open();
        SqlCommand cmd = new SqlCommand("select * from userInfo where username=@username", cn);
        cmd.Parameters.AddWithValue("@username", username);
        cmd.ExecuteNonQuery();
        SqlDataAdapter da = new SqlDataAdapter(cmd);
        DataSet ds = new DataSet();
        da.Fill(ds);
        cn.Close();
        XmlDataDocument xmldata = new XmlDataDocument(ds);
        XmlElement xmlElement = xmldata.DocumentElement;
        return xmlElement;



    } 

thanks

Answer 1

Well the error message seems reasonably clear - GetUserDetails is returning XElement (from LINQ to XML) rather than XmlDocument (from the older API).

This shouldn't be a problem though, as basically you just need to select an element and create an XmlReader from it. It looks like your code can just be changed to:

protected void BindUserDetails(string userName)
{
    UserService.ServiceSoapClient client = new UserService.ServiceSoapClient();
    XElement element = client.GetUserDetails(userName);
    if (element != null)
    {
        DataSet dsresult = new DataSet();
        XmlReader reader = element.CreateReader();
        dsresult.ReadXml(reader, XmlReadMode.Auto);
        gvUserDetails.DataSource = dsresult;
    }
    else
    {
        gvUserDetails.DataSource = null;
    }
    gvUserDetails.DataBind();
}

You could potentially refactor that further to extract the "convert XElement to DataSet " functionality:

// You could *consider* making this an extension method
public static DataSet ToDataSetOrNull(XElement source)
{
    if (source == null)
    {
        return null;
    }
    DataSet result = new DataSet();
    result.ReadXml(source.CreateReader(), XmlReadMode.Auto);
    return result;
}

Then your BindUserDetails code is just:

protected void BindUserDetails(string userName)
{
    UserService.ServiceSoapClient client = new UserService.ServiceSoapClient();
    gvUserDetails.DataSource = ToDataSetOrNull(client.GetUserDetails(userName));
    gvUserDetails.DataBind();
}

... and if you have other "BindXyzDetails" methods, they'll be similarly short.