factory.cs

using System.Diagnostics;
using System.Runtime.InteropServices;

namespace TXTextControl.Diagnostics {

    /// <summary>
    /// Singleton factory class to return and manage ServerTextControl instances.
    /// </summary>
    public sealed class ServerTextControlFactory {

        // private fields
        private static readonly ServerTextControlFactory _instance =
            new ServerTextControlFactory();
        private List<ServerTextControl> _activeControls;

        [DllImport("User32")]
        extern public static int GetGuiResources(IntPtr hProcess, int uiFlags);

        private enum ResourceType {
            Gdi = 0,
            User = 1
        }

        static ServerTextControlFactory() {

        }

        private ServerTextControlFactory() {
            _activeControls = new List<ServerTextControl>();
        }

        /// <summary>
        /// Returns the singleton instance.
        /// </summary>
        public static ServerTextControlFactory Instance {
            get {
                return _instance;
            }
        }

        /// <summary>
        /// Returns the number of active ServerTextControls that are not disposed.
        /// </summary>
        public int Count {
            get {
                return _activeControls.Count;
            }
        }

        /// <summary>
        /// Returns the total number of USER handles in current process.
        /// </summary>
        public int UserHandles {
            get {
                var processHandle = Process.GetCurrentProcess().Handle;
                return GetGuiResources(processHandle, (int)ResourceType.User);
            }
        }

        /// <summary>
        /// Returns the total number of GDI handles in current process.
        /// </summary>
        public int GdiHandles {
            get {
                var processHandle = Process.GetCurrentProcess().Handle;
                return GetGuiResources(processHandle, (int)ResourceType.Gdi);
            }
        }

        /// <summary>
        /// Disposes all active ServerTextControl instances.
        /// </summary>
        public int DisposeAll() {

            int numControls = _activeControls.Count;
            int i;

            for (i = 0; i < numControls; i++) {
                _activeControls[0].Dispose();
            }

            return i;
        }

        /// <summary>
        /// Returns a new ServerTextControl instance and adds it to the list of
        /// active instances.
        /// Returns null in case a new ServerTextControl instance could not be created.
        /// </summary>
        public ServerTextControl? CreateServerTextControl() {

            // create a new ServerTextControl instance and listen for the disposal
            ServerTextControl serverTextControl = new ServerTextControl();

            // trying to create - if creation fails, dispose the object and return null
            if (serverTextControl.Create() == false) {
                serverTextControl.Dispose();
                return null;
            }

            // attached the Disposed event to clean up list of instances
            serverTextControl.Disposed += ServerTextControl_Disposed;

            // add to list of instances
            _activeControls.Add(serverTextControl);

            return serverTextControl;
        }

        private void ServerTextControl_Disposed(object sender, EventArgs e) {
            // remove from list of instances
            _activeControls.Remove((ServerTextControl)sender);
        }
    }
}