pinvoke.net: Edit: user32.registerwindowmessage

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Summary: The RegisterWindowMessage API

!!!!C# Signature:
 /// <summary>
 /// Defines a new window message that is guaranteed to be unique throughout the system. The message value can be used
 /// when sending or posting messages.
 /// <para>
 /// Go to https://msdn.microsoft.com/en-us/library/windows/desktop/ms644947%28v=vs.85%29.aspx for more
 /// information.
 /// </para>
 /// </summary>
 /// <param name="msg">C++ ( lpString [in]. Type: LPCTSTR ) The message to be registered.</param>
 /// <returns>
 /// C++ ( Type: UINT ) If the message is successfully registered, the return value is a message identifier in the
 /// range 0xC000 through 0xFFFF. If the function fails, the return value is zero. To get extended error
 /// information, call GetLastError.
 /// </returns>
 /// <remarks>
 /// The <see cref="RegisterWindowMessage" /> function is typically used to register messages for communicating between
 /// two cooperating applications. If two different applications register the same message string, the applications
 /// return the same message value.The message remains registered until the session ends. Only use
 /// <see cref="RegisterWindowMessage" /> when more than one application must process the same message.For sending
 /// private messages within a window class, an application can use any integer in the range WM_USER through 0x7FFF.
 /// (Messages in this range are private to a window class, not to an application.For example, predefined control
 /// classes such as BUTTON, EDIT, LISTBOX, and COMBOBOX may use values in this range.)
 /// </remarks>
 /// <example>
 /// <code><![CDATA[
 /// //provide a private internal message id
 /// private UInt32 queryCancelAutoPlay = 0;
 /// 
 /// [DllImport("user32.dll", SetLastError=true, CharSet=CharSet.Auto)]
 /// static extern uint RegisterWindowMessage(string lpString);
 /// 
 /// /* only needed if your application is using a dialog box and needs to respond to a "QueryCancelAutoPlay" message, it cannot simply return TRUE or FALSE.
 /// [DllImport("user32.dll")]
 /// static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);
 /// */
 /// 
 /// protected override void WndProc(ref Message m)
 /// {
 /// //calling the base first is important, otherwise the values you set later will be lost
 /// base.WndProc(ref m);
 /// 
 /// //if the QueryCancelAutoPlay message id has not been registered...
 /// if (queryCancelAutoPlay == 0)
 /// queryCancelAutoPlay = RegisterWindowMessage("QueryCancelAutoPlay");
 /// 
 /// //if the window message id equals the QueryCancelAutoPlay message id
 /// if ((UInt32)m.Msg == queryCancelAutoPlay)
 /// {
 /// /* only needed if your application is using a dialog box and needs to
 /// * respond to a "QueryCancelAutoPlay" message, it cannot simply return TRUE or FALSE.
 /// SetWindowLong(this.Handle, 0, 1);
 /// */
 /// m.Result = (IntPtr)1;
 /// }
 /// }
 /// ]]></code>
 /// </example>
 [DllImport("user32.dll", SetLastError=true, CharSet=CharSet.Auto)]
 static extern uint RegisterWindowMessage(string lpString);
!!!!VB.NET Signature:
 <DllImport("user32.dll", CharSet:=CharSet.Auto)> _
 Private Shared Function RegisterWindowMessage( _
 ByVal lpString As String) As UInteger
 End Function
!!!!Oxygene.NET Signature:
 [DllImport("user32.dll", SetLastError := true, CharSet := CharSet.Auto)]
 class method RegisterWindowMessage(lpString: String): UInt32; external;
!!!!VB Signature:
 Declare Function RegisterWindowMessage Lib "user32.dll" (ByVal lpString As String) As Integer
!!!!User-Defined Types:
None.

!!!!Notes:

'''Unicode notification'''
        DllImport("user32.dll", EntryPoint = "RegisterWindowMessageW", SetLastError = true)]
        private static extern int RegisterWindowMessage(string lpString);

If you use the above notation, it will not be the Unicode call, Always add the CharSet=CharSet.Auto or CharSet.Unicode

In VB6 the definition for the API declaration should be:
Declare Function RegisterWindowMessage Lib "user32.dll" Alias "RegisterWindowMessageW" (ByVal lpString As long) As Integer

strMessageToRegister = "QueryCancelAutoPlay"
        lngWindowMsg = RegisterWindowMessage(StrPtr(strMessageToRegister))
If you use RegisterWindowMessage("QueryCancelAutoPlay") it will NOT work, put the "QueryCancelAutoPlay" in a variable or constant and use that one.

!!!!Tips & Tricks:
Please add some!

!!!!Sample Code:
'''VB.NET Sample Code'''
        Dim MessageID As Integer
        MessageID = RegisterWindowMessage("QueryCancelAutoPlay")

'''C# Sample Code'''
 //Register the message
 lMsg = Win32.RegisterWindowMessage("WM_HTML_GETOBJECT");
 //Get the object
 Win32.SendMessageTimeout(windowHandle, lMsg, IntPtr.Zero, IntPtr.Zero, SendMessageTimeoutFlags.SMTO_ABORT_IF_HUNG, 1000, out lRes);
 if(lRes != IntPtr.Zero)
 {
 	//Get the object from lRes
	htmlDoc= (mshtml.IHTMLDocument)Win32.ObjectFromLresult(lRes, IID_IHTMLDocument, IntPtr.Zero);
	return htmlDoc;
 }

'''C# Sample Code'''
 //provide a private internal message id
 private UInt32 queryCancelAutoPlay = 0;

[DllImport("user32.dll", SetLastError=true, CharSet=CharSet.Auto)]
 static extern uint RegisterWindowMessage(string lpString);

/* only needed if your application is using a dialog box and needs to 
 * respond to a "QueryCancelAutoPlay" message, it cannot simply return TRUE or FALSE.
 [DllImport("user32.dll")]
 static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);
 */

protected override void WndProc(ref Message m)
 {
 	//calling the base first is important, otherwise the values you set later will be lost
 	base.WndProc (ref m);
 
	//if the QueryCancelAutoPlay message id has not been registered...
 	if (queryCancelAutoPlay == 0)
 		queryCancelAutoPlay = RegisterWindowMessage("QueryCancelAutoPlay");
 
	//if the window message id equals the QueryCancelAutoPlay message id
 	if ((UInt32)m.Msg == queryCancelAutoPlay)
	{
		/* only needed if your application is using a dialog box and needs to
 		* respond to a "QueryCancelAutoPlay" message, it cannot simply return TRUE or FALSE.
 		SetWindowLong(this.Handle, 0, 1);
 		*/
 		m.Result = (IntPtr)1;
	}
 } //WndProc

!!!!Alternative Managed API:
Do you know one?  Please contribute it!

Documentation: RegisterWindowMessage@msdn on MSDN