C#

// Create the new node. 
TreeNode newNode = new TreeNode();
newNode.Text = row["CategoryName"].ToString(); 
newNode.Value = row["CategoryID"].ToString();        

// Set the PopulateOnDemand property to true so that the child nodes can be 
// dynamically populated.
newNode.PopulateOnDemand = true;

// Set additional properties for the node.
newNode.SelectAction = TreeNodeSelectAction.Expand;

// Add the new node to the ChildNodes collection of the parent node.
node.ChildNodes.Add(newNode);

private _myClass;
public void SetupDomain(string configFile, string domainName)
{
  AppDomainSetup setup = new AppDomainSetup();
  setup.ConfigurationFile = configFile;
  AppDomain domain = AppDomain.CreateDomain(domainName, null, setup);

  _myClass = (MyDllClass)domain.CreateInstanceAndUnwrap("MyDll", "MyDll.MyDllClass");
}

 SetupDomain("MyDll.Dll.Config", "My domain");
int value = _myClass.GetConfigItem();

public class MyLibClass
{
	private string m_configName = "MyLib.dll.config";
	private string keyName = "APP_CONFIG_FILE";

	public MyLibClass()
	{
		Reload();
	}

	public void Reload()
	{
		// build the path to the config file
		string configPath = System.IO.Path.Combine(Environment.CurrentDirectory, m_configName);

		// get the name of the hosting application's config file (so we can reset it later)
		string appConfigFile = AppDomain.CurrentDomain.GetData(keyName).ToString();

		// plug in the DLL's config file path/name
		AppDomain.CurrentDomain.SetData(keyName, configPath);

		// load some app settings using the ConfigurationManager class
		string xyz = ConfigurationManager.AppSettings["mySetting"];

		// reset the current config file to the hosting app's config file
		AppDomain.CurrentDomain.SetData(keyName, appConfigFile);
	}
}

[System.Runtime.InteropServices.DllImport ( "Winmm" , SetLastError=true , EntryPoint="PlaySound" )]
private static extern bool
API_PlaySound
(
    string        pszSound
,
    System.IntPtr hmod
,
    uint          fdwSound
) ;