I have a class which needs to be a Singleton. It must also be able to load and save its field data in an xml file.
The following method will return a new instance,
I used to run into all sorts of bugs making an Xml Singleton class and ended up scrapping it as I had handles all over the place. I replaced it with using two ways. One a read-only version that was for reading data, and a second Using method/statement for writing changes.
This in general is the pattern I use:
public class Settings : IDisposable
{
string file = "my settings file";
XElement root;
private Settings()
{
root = XElement.Load(file);
}
private void Dispose()
{
root.Save(file);
}
public static Settings Read { get { return new Settings(); } } // return read-only version
public static void Write(Action<Settings> handler)
{
using(Setting settings = new Settings())
handler(settings);
}
// below here is implentation specific
public XElement Root { get { return root; } }
public string SettingA
{
get { return (string)(Root.Attribute("SettingA") ?? (object)string.Empty); }
set { Set(Root, "SettingsA", value, true); }
}
// I wrote this for another StackOverflow thread
/// <summary>
/// Set any value via its .ToString() method.
/// <para>Returns XElement of source or the new XElement if is an ELEMENT</para>
/// </summary>
/// <param name="isAttribute">true for ATTRIBUTE or false for ELEMENT</param>
/// <returns>source or XElement value</returns>
private XElement Set(XElement source, string name, object value, bool isAttribute)
{
string sValue = value.ToString();
XElement eValue = source.Element(name), result = source;
XAttribute aValue = source.Attribute(name);
if (null != eValue)
eValue.ReplaceWith(result = new XElement(name, sValue));
else if (null != aValue)
aValue.ReplaceWith(new XAttribute(name, sValue));
else if (isAttribute)
source.Add(new XAttribute(name, sValue));
else
source.Add(result = new XElement(name, sValue));
return result;
}
/// <summary>
/// Replace with for XAttribute
/// </summary>
/// <param name="source"></param>
/// <param name="value"></param>
/// <returns></returns>
public static XAttribute ReplaceWith(this XAttribute source, XAttribute value)
{
XElement parent = source.Parent;
if (null == parent)
throw new Exception("Source has no parent");
source.Remove();
parent.Add(value);
return value;
}
}
I've not used the serializer, so don't know if my pattern will fit for you. I prefer XElement.
So to use this you'd probably write a singleton class that makes use of your non-singleton XmlSerialize class. You'd only access it through the singleton.
But this is how I'd end up using it as is:
string settingA = Settings.Read.SettingA;
To save a value it would be:
Settings.Write(s => s.SettingA = "new value");
why dont you have something like
public Class TheClassHoldingYourObject
{
private static XmlSerializer _instance;
public static Settings Load()
{
if(_instance != null) return _instance
using (Stream stream = File.OpenRead(FileName))
{
XmlSerializer serializer = new XmlSerializer(typeof(Settings));
return (Settings)serializer.Deserialize(stream);
}
}
}
Now you will always get the same instance