XMLSerializer writes invalid XML when serializing a class (Sometimes)

Question

My goal is to be able to share configration settings amongst apps. For example I want to be able to use a WinForm app to set and save the settings and have a console app be able to read those settings and run as a scheduled task. The approach I tried is to create a SharedSettings class that is referenced by both the Winform app and the Console app. In this class there is nothing but public string properties like so.

public class SharedSettings
{
    public string URL { get; set; }
    public string DestUser { get; set; }
    public string RelScript { get; set; }
}

I am using the following to serialize the instance of the SharedSettings class

SharedSettings settings = new SharedSettings();

settings.RelScript = this.txtRelScript.Text;
settings.URL = this.txtURL.Text;
settings.DestUser = this.txtDestUser.Text;

XmlSerializer dehydrator = new XmlSerializer(settings.GetType());
System.IO.FileStream fs = new FileStream(this.configFilePath, FileMode.OpenOrCreate);
dehydrator.Serialize(fs, settings); 

and this to Deserialize it and populate the fields in the Form

SharedSettings settings = new SharedSettings();
XmlSerializer dehydrator = new XmlSerializer(settings.GetType());
System.IO.FileStream fs = new FileStream(this.configFile, FileMode.Open);
settings = (SharedSettings)dehydrator.Deserialize(fs);

this.txtRelScript.Text = settings.RelScript;
this.txtURL.Text = settings.URL;
this.DestUser.Text = settings.DestUser;

Every once in a while maybe one out of every five times I run it the XML file that is created in not valid XML. Here is an example

<?xml version="1.0"?>
<SharedSettings xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"     xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<ProjectName>test2</ProjectName>
<URL />
<DestUser>test3</DestUser>
<RelScript>D:\Events.dll</ReleaseScript>
</SharedSettings>ttings>

Notice the last line. ttings> What am I doing wrong in Serializing my class?

Answer 1

It looks like the previous run through wrote out a longer file. The use of FileMode.OpenOrCreate in your serialization code doesn't truncate the previous file, so it is partly overwritten.

Use FileMode.Create instead.

See the documentation here.