Check if XElement is null globally

Question

I have a class what takes care of reading and holding the XML file. Right now a simple version of it looks like this:

public class EstEIDPersoConfig
{
    public bool LaunchDebugger { get ; set; }
    public string Password { get; set; }
    public int Slot { get; set; }
    public string Reader { get; set; }
    public string TestInput { get; set; }
    public bool Logging { get; set; }

    public EstEIDPersoConfig()
    {
        XElement xml = XElement.Load(myxml.xml);
        XElement Configuration = xml.Element("Configuration");

        LaunchDebugger = Convert.ToBoolean(Configuration.Element("LaunchDebugger").Value);
        Password = Configuration.Element("Password").Value;
        Slot = Convert.ToInt32(Configuration.Element("Slot").Value);
        Reader = Configuration.Element("Reader").Value;
        TestInput = Configuration.Element("TestInput").Value;
        Logging = Convert.ToBoolean(Configuration.Element("Logging").Value);
     }
 }

And there will be more later. so the problem is that if some element does not exist in xml i get System.NullReferenceException. So i need to check if the element is null or not. Heres one way to do this:

var value = Configuration.Element("LaunchDebugger").Value;
if (value != null)
    LaunchDebugger = Convert.ToBoolean(value);
else
    throw new Exception("LaunchDebugger element missing from xml!");

But doing that for every element would be just too much. So i need some good ideas how to simplify this system so it wouldn't end up in 1000 lines of code.

EDIT: Edited the last code snippet, the idea was not to set a default value, idea was to notify the user that this element whats null is missing from the xml.

Answer 1

The idea here comes directly from abatischev's answer so he deserves the credit.

As perscribed by Microsoft here you can just cast the XElement to the type you desire.

LaunchDebugger = (bool?)Configuration.Element("LaunchDebugger");

if you want to handle the null case I guess you could do

LaunchDebugger = (bool)(Configuration.Element("LaunchDebugger") ?? true);

or perhaps

LaunchDebugger = (bool)(Configuration.Element("LaunchDebugger") ?? false);

depending on your business logic. If you do the same coalescene for a specific type it may be appropriate to wrap this one liner in a method, extension or otherwise but I'm uncertain it would add much.

Answer 2

(bool)Configuration.Element("LaunchDebugger")

or

(bool?)Configuration.Element("LaunchDebugger")

should not throw exception.

See MSDN:

• XElement Explicit Conversion (XElement to Boolean)
• XElement Explicit Conversion (XElement to Nullable<Boolean>)

Answer 3

I have an extension method that I use for just this kind of thing:

    public static T GetValue<T>(
            this XElement @this,
            XName name, 
            Func<XElement, T> cast, 
            Func<T> @default)
    {
        var e = @this.Element(name);
        return (e != null) ? cast(e) : @default();
    }

It gives you the casting required and also a default value factory.

Here's how you'd use it:

LaunchDebugger = Configuration.GetValue("LaunchDebugger",
    x => Convert.ToBoolean(x), () => false);
Password = Configuration.GetValue("CMKPassword", x => (string)x, () => "");
Slot = Configuration.GetValue("CMKSlot", x => (int)x, () => -1);
Reader = Configuration.GetValue("Reader", x => (string)x, () => "");
TestInput = Configuration.GetValue("TestInput", x => (string)x, () => "");
Logging = Configuration.GetValue("Logging",
    x => Convert.ToBoolean(x), () => false);

Answer 4

Extract the logic to a method and have overloaded methods for Int32,boolean and other data types conversion.

public static void GetElementValue(XElement xElement, string parameter, out bool value)
    {
        var stringValue = xElement.Element(parameter).Value;
        value = false;
        if (value != null)
            value = Convert.ToBoolean(stringValue);
    }

Answer 5

You can define a method to extract the value for you and do some checking on null there. So wrap the value retrieval in your own method like so:

public string GetXMLValue(XElement config, string elementName){
    var element = Configuration.Element(elementName);

    if(element == null)
        return String.Empty;

    return element.Value;
}

Of course you can extend this to work correctly with parsing to boolean etc.