Q:

How to programmatically modify assemblyBinding in app.config?

I am trying to change the bindingRedirect element at install time by using the XmlDocument class and modifying the value directly. Here is what my app.config looks like:
<configuration>
    <configSections>
        <sectionGroup name="applicationSettings" type="System.Configuration.ApplicationSettingsGroup, System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">            
            ...
        </sectionGroup>      
    </configSections>
    <runtime>
      <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
        <dependentAssembly>
          <assemblyIdentity name="MyDll" publicKeyToken="31bfe856bd364e35"/>
          <bindingRedirect oldVersion="0.7" newVersion="1.0"/>
        </dependentAssembly>
     </assemblyBinding>
    </runtime>    
...
</configuration>

I then try to use the following code to change 1.0 to 2.0
private void SetRuntimeBinding(string path, string value)
{
    XmlDocument xml = new XmlDocument();

    xml.Load(Path.Combine(path, "MyApp.exe.config"));
    XmlNode root = xml.DocumentElement;

    if (root == null)
    {
        return;
    }

    XmlNode node = root.SelectSingleNode("/configuration/runtime/assemblyBinding/dependentAssembly/bindingRedirect/@newVersion");

    if (node == null)
    {
        throw (new Exception("not found"));
    }

    node.Value = value;

    xml.Save(Path.Combine(path, "MyApp.exe.config"));
}

However, it throws the 'not found' exception. If I back the path up to /configuration/runtime it works. However once I add assemblyBinding, it does not find the node. Possibly this has something to do with the xmlns? Any idea how I can modify this? ConfigurationManager also does not have access to this section.

A:

I found what I needed. The XmlNamespaceManager is required as the assemblyBinding node contains the xmlns attribute. I modified the code to use this and it works:
    private void SetRuntimeBinding(string path, string value)
    {
        XmlDocument doc = new XmlDocument();

        try
        {
            doc.Load(Path.Combine(path, "MyApp.exe.config"));
        }
        catch (FileNotFoundException)
        {
            return;
        }

        XmlNamespaceManager manager = new XmlNamespaceManager(doc.NameTable);
        manager.AddNamespace("bindings", "urn:schemas-microsoft-com:asm.v1");

        XmlNode root = doc.DocumentElement;

        XmlNode node = root.SelectSingleNode("//bindings:bindingRedirect", manager);

        if (node == null)
        {
            throw (new Exception("Invalid Configuration File"));
        }

        node = node.SelectSingleNode("@newVersion");

        if (node == null)
        {
            throw (new Exception("Invalid Configuration File"));
        }

        node.Value = value;

        doc.Save(Path.Combine(path, "MyApp.exe.config"));
    }

A:

Sounds like you've got your configuration file tweak working now, but I thought you might still be interested in how to adjust binding redirects at run time. The key is to use the AppDomain.AssemblyResolve event, and the details are in this answer. I prefer it over using the configuration file, because my version number comparison can be a bit more sophisticated and I don't have to tweak the configuration file during every build.

