使用where子句的XElement linq to XML查询的“上下文实例”

Question

I want to return a list of string values from an XElement collection and I get this error when constructing my code and don't see what I'm missing.

Here's a section of the class I've written concering the problem:

private XElement _viewConfig;

public ViewConfiguration(XElement vconfig)
{

    _viewConfig = vconfig;
}

public List<string> visibleSensors()
{

    IEnumerable<string> sensors = (from el in _viewConfig
                                   where el.Attribute("type").Value == "valueModule"
                                         && el.Element.Attribute("visible") = true
                                   select el.Element.Attribute("name").Value);

    return sensors.ToList<string>();
}

The XElement collection is of the form

<module name="temperature" type="valueModule" visible="true"></module>
<module name="lightIntensity" type="valueModule" visible="true"></module>
<module name="batteryCharge" type="valueModule" visible="true"></module>
<module name="VsolarCells" type="valueModule" visible="false"></module>

Answer 1

First of all XElement is not an IEnumerable therefore the first line from el in _viewConfig is not valid. If this is coming from a valid XML file, I presume the <module> elements are contained inside a parent element (eg, <modules> ). If you make _viewConfig to point to modules then the following will work:

IEnumerable<string> sensors = (
    from el in _viewConfig.Elements()
    where el.Attribute("type").Value == "valueModule"
          && el.Attribute("visible").Value == "true"
    select el.Attribute("name").Value);

Also note that type of el is XElement , therefore it doesn't have a property called Element which I also removed from above (along with a few syntax errors that I had to fix: usage of == instead of = for comparison, and using string literal "true" instead of boolean true to compare the value of an attribute textual value).