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 )<br /> The message to be registered.</param>
/// <returns>
///     C++ ( Type: UINT )<br /> 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.<br /><br /> 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.
///     <br />(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!

Please edit this page!

Do you have...

• helpful tips or sample code to share for using this API in managed code?
• corrections to the existing content?
• variations of the signature you want to share?
• additional languages you want to include?

Select "Edit This Page" on the right hand toolbar and edit it! Or add new pages containing supporting types needed for this API (structures, delegates, and more).