Vanara/PInvoke/User32/BasicMessageWindow.cs

using System;
using System.Runtime.InteropServices;
using static Vanara.PInvoke.Kernel32;
using static Vanara.PInvoke.User32;

namespace Vanara.PInvoke
{
	/// <summary>A filter method that handles messages sent to a window.</summary>
	/// <param name="hwnd">A handle to the window.</param>
	/// <param name="msg">The MSG.</param>
	/// <param name="wParam">Additional message information. The contents of this parameter depend on the value of the uMsg parameter.</param>
	/// <param name="lParam">Additional message information. The contents of this parameter depend on the value of the uMsg parameter.</param>
	/// <param name="lReturn">The return value is the result of the message processing and depends on the message sent.</param>
	/// <returns>
	/// <see langword="true"/> if the message is handled and <see cref="DefWindowProc(HWND, uint, IntPtr, IntPtr)"/> should not be called;
	/// <see langword="false"/> otherwise.
	/// </returns>
	[UnmanagedFunctionPointer(CallingConvention.Winapi)]
	public delegate bool BasicMessageWindowFilter(HWND hwnd, uint msg, IntPtr wParam, IntPtr lParam, out IntPtr lReturn);

	/// <summary>Simple window to process messages.</summary>
	/// <seealso cref="System.MarshalByRefObject"/>
	/// <seealso cref="System.IDisposable"/>
	/// <seealso cref="Vanara.PInvoke.IHandle"/>
	public class BasicMessageWindow : MarshalByRefObject, IDisposable, IHandle
	{
		private readonly SafeHWND hwnd;
		private bool isDisposed;

		/// <summary>Initializes a new instance of the <see cref="BasicMessageWindow"/> class.</summary>
		/// <param name="callback">Specifies the callback method to use to process messages.</param>
		public BasicMessageWindow(BasicMessageWindowFilter callback = null)
		{
			MessageFilter = callback;
			ClassName = $"{GetType().Name}+{Guid.NewGuid()}";

			hwnd = CreateWindow();
		}

		/// <summary>Finalizes an instance of the <see cref="BasicMessageWindow"/> class.</summary>
		~BasicMessageWindow() => Dispose(false);

		/// <summary>Gets the name of the class.</summary>
		/// <value>The name of the class.</value>
		public string ClassName { get; private set; }

		/// <summary>Gets the handle.</summary>
		/// <value>The handle.</value>
		public HWND Handle => hwnd;

		/// <summary>Gets or sets the callback method used to filter window messages.</summary>
		/// <value>The callback method.</value>
		public BasicMessageWindowFilter MessageFilter { get; set; }

		/// <summary>Performs application-defined tasks associated with freeing, releasing, or resetting unmanaged resources.</summary>
		public void Dispose()
		{
			Dispose(true);
			System.GC.SuppressFinalize(this);
		}

		/// <summary>Returns the value of the handle field.</summary>
		/// <returns>An IntPtr representing the value of the handle field.</returns>
		IntPtr IHandle.DangerousGetHandle() => (IntPtr)Handle;

		/// <summary>
		/// Method used to create the window. When overriding, the <c>hWnd</c> field must be set to the handle of the created window.
		/// </summary>
		protected virtual SafeHWND CreateWindow()
		{
			var hInst = GetModuleHandle();
			var wcx = new WNDCLASSEX { cbSize = (uint)Marshal.SizeOf(typeof(WNDCLASSEX)), lpfnWndProc = WndProc, hInstance = hInst, lpszClassName = ClassName };
			var atom = Win32Error.ThrowLastErrorIfNull(Macros.MAKEINTATOM(RegisterClassEx(wcx)));
			return Win32Error.ThrowLastErrorIfInvalid(CreateWindowEx(lpClassName: atom, hWndParent: HWND.HWND_MESSAGE, hInstance: hInst));
		}

		/// <summary>Releases unmanaged and - optionally - managed resources.</summary>
		/// <param name="disposing">
		/// <see langword="true"/> to release both managed and unmanaged resources; <see langword="false"/> to release only unmanaged resources.
		/// </param>
		protected virtual void Dispose(bool disposing)
		{
			if (isDisposed)
				return;
			isDisposed = true;

			hwnd?.Dispose(); // Calls DestroyWindow
			UnregisterClass(ClassName, GetModuleHandle());
			ClassName = null;
		}

		private IntPtr WndProc(HWND hwnd, uint msg, IntPtr wParam, IntPtr lParam) =>
			MessageFilter is null || !MessageFilter.Invoke(hwnd, msg, wParam, lParam, out var lRet)
				? DefWindowProc(hwnd, msg, wParam, lParam)
				: lRet;
	}
}