Problem writing self closing null value to SettingElement in app.config

Question

I am using the following code to write/edit the app.config file at runtime that allows the user to change ApplicationSettings however, I have a problem when writing pr saving null values.

Here is the code:

            Dim config As Configuration = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None)  
            Dim applicationSectionGroup As ConfigurationSectionGroup = config.GetSectionGroup("applicationSettings")  
  
            Dim strAppName As String = System.Reflection.Assembly.GetExecutingAssembly.GetName().Name  
            Dim applicationConfigSection As ConfigurationSection = applicationSectionGroup.Sections(strAppName & ".My.MySettings")  
            Dim clientSection As ClientSettingsSection = CType(applicationConfigSection, ClientSettingsSection)  
  
            ' set a value to that specific property  
            Dim applicationSetting As SettingElement  
  
            applicationSetting = clientSection.Settings.Get("Testsetting")  
            applicationSetting.Value.ValueXml.InnerText = Nothing  
            
            ' without this, saving won't work  
            applicationConfigSection.SectionInformation.ForceSave = True  
            ' save  
            config.Save()  

The problem is, when I save null values with this code, the Value tag is not written correctly. It's writing the tag as follows:

The problem is, when I read the tag using My.Settings.Testsetting, it's being read by vb.net as multiple spaces instead of a null or empty string. I know I can use a trim statement to read the settings and clear the spaces but, I would rather find a way to save the empty value correctly instead of working around the problem.

In my production code, I am passing the Value in as a string but for testing purposes above, I have been trying to find a way to save it as a self-closing value like
<value />

That's how visual studio saves the tag with a null value when saved from the Project Property Settings screen.

Any help would be really appreciated.

Thanks

Answer 1

I wrote the following in C#, converted to VB.

My.Settings.Default.Testsetting = ""
My.Settings.Default.Save()
Dim config As Configuration = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None)
config.AppSettings.Settings.Remove("Testsetting")
config.Save()

Result

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <userSettings>
        <DataBindValidate.Properties.Settings>
            <setting name="Testsetting" serializeAs="String">
                <value />
            </setting>
        </DataBindValidate.Properties.Settings>
    </userSettings>
</configuration>

Answer 2

After a LOT of late nights and unpaid OT this weekend, I found the solution.

The following code allows me to change how the Value Node is written in the app.config (.exe.config) file when the value is null or an empty string.

Public Function WriteApplicationSettingValue(strSetting As String, strValue As String) As Boolean

        Try
            ' this gets the applicationSettings section (and the inner section 'inoBIBooks.My.MySettings')
            Dim config As Configuration = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None)
            Dim applicationSectionGroup As ConfigurationSectionGroup = config.GetSectionGroup("applicationSettings")

            Dim strAppName As String = System.Reflection.Assembly.GetExecutingAssembly.GetName().Name
            Dim applicationConfigSection As ConfigurationSection = applicationSectionGroup.Sections(strAppName & ".My.MySettings")
            Dim clientSection As ClientSettingsSection = CType(applicationConfigSection, ClientSettingsSection)

            ' set a value to that specific property
            Dim applicationSetting As SettingElement = clientSection.Settings.Get(strSetting)

            If Not IsNothing(applicationSetting) Then
                'saving empty strings causes the <VALUE> node/tag to be written incorrectly in the app.config file incorrently
                'The <Value> and <Value /> are written on 2 different lines which when read back through My.Settings causes
                'the vealue appears as "       " instead of "".  To overcome this problem, we have to create our own
                'XML node and override the XMLValue node in the SettingElement
                If String.IsNullOrEmpty(strValue) Then
                    Dim doc As New XmlDocument()
                    doc.LoadXml("<value />")

                    Dim SelfClosingValueNode As System.Xml.XmlNode = doc.SelectSingleNode("value")
                    applicationSetting.Value.ValueXml = SelfClosingValueNode
                Else
                    applicationSetting.Value.ValueXml.InnerText = strValue
                End If

                ' without this, saving won't work
                applicationConfigSection.SectionInformation.ForceSave = True
                ' save
                config.Save()

                Return True
            Else
                Return False
            End If

        Catch ex As Exception
            MsgBox("The following error occurred while attempting to write to the application settings file." & vbCrLf & vbCrLf & ex.Message, MsgBoxStyle.Exclamation)
            Return False
        End Try

    End Function