How to change the MessageBox window (Add controls and change texts)?

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Introduction

In this article we will learn how to add controls to a MessageBox or how to change its button texts. You can use this method to create (full) Multilanguage programs (Just a suggestion!). There are some ways to do this and I chose the hooking method.

Steps of Hooking a MessageBox

To hook a MessageBox:

• Use SetWindowsHookEx () function with WH_CALLWIND and pass it to a hookproc.
• Declare a hook procedure.
• In the hookproc use the SetWindowLong () function to handle the MessageBox window Creation process (Maybe it is a good name for this).
• Declare a CALLBACK function to handle the MessageBox window creation process.
• Pass the CALLBACK function as the new long parameter in the SetWindowLong () function.
• And at the end, place your codes in the CALLBACK function (codes for window creation).

SetWindowsHookEx () function

This function installs a hook procedure. Using this function you can hook windows events. In other words when you install a hook procedure you tell the system to notify you when the wanted event is called.

As MSDN says: The SetWindowsHookEx function installs an application-defined hook procedure into a hook chain. You would install a hook procedure to monitor the system for certain types of events. These events are associated either with a specific thread or with all threads in the same desktop as the calling thread.

How to Install a hook procedure using SetWindowsHookEx () function?

g_hHook = SetWindowsHookEx (WH_CALLWNDPROC,
                               (HOOKPROC)SetHook,
                               NULL,
                               GetCurrentThreadId ());

Where g_hHook is a global variable and the SetHook is my HookProc;

What is WH_CALLWNDPROC?

Use this parameter to install a hook procedure that monitors messages before the system sends them to the destination window procedure (MSDN).

Declaring a HookProcedure

Use the following declarations in your header file:

LRESULT CALLBACK SetHook(int nCode,WPARAM wParam,LPARAM lParam);

This will declare a hook procedure by name SetHook. See this code snippet:

LRESULT CALLBACK SetHook(int nCode,WPARAM wParam,LPARAM lParam)
{
if (nCode==HC_ACTION)
{
    CWPSTRUCT* pwp = (CWPSTRUCT*)lParam;
    
    if (pwp->message==WM_INITDIALOG)
        
    oldProc=(WNDPROC)SetWindowLong(pwp>hwnd,
GWL_WNDPROC,(LONG)HookWndProc); 
}
return CallNextHookEx(g_hHook,nCode,wParam,lParam);
}

This code snippet is my SetHook procedure.

What is GWL_WNDPROC?

This parameter sets a new address for the window procedure. (I think it is enough).

What is CWPSTRUCT?

This is a structure that contains information about window messages like a handle to that window (hwnd). We pass a pointer of this structure to use the hwnd member in the callback function.

And the HookWndProc is a function that processes the window creation codes.

Handling the window creation process

To do this, you must declare a CALLBACK function.

LRESULT CALLBACK HookWndProc(HWND hWnd,UINT uMsg,WPARAM wParam,LPARAM lParam);

This is my HookWndProc procedure.

LRESULT CALLBACK HookWndProc(HWND hWnd,UINT uMsg,WPARAM wParam,LPARAM lParam)
{
    //Let OS to perform basic operation
    LRESULT rc = CallWindowProc( oldProc, hWnd, uMsg, wParam, lParam );

    //If MessageBox wanted to initialized, do something
    if (uMsg==WM_INITDIALOG)
    {
        if (m_hIcon)
            SetIcon(hWnd,m_hIcon);
            CreateButton(hWnd);    

        if (m_strCaption)
            SetCaption(hWnd);
    }
    if (uMsg==WM_COMMAND&&wParam==IDC_CHECKBOX)
        //If user clicked the check box handle it!
        SetOut(wParam);
    if (uMsg==WM_NCDESTROY)
        //On exit Uninstall the hook procedure
        //If we don't do that every message box will have 
        //A check box on it!
        UnInstallHook(g_hHook);
return rc;
}

The main operations are done. I mean the hwnd. After having this hwnd, we can do everything to the MessageBox window. But don’t forget to call CallWindowProc function.

What does the CallWindowProc do?

According to MSDN: The CallWindowProc function passes message information to the specified window procedure.

I used this function because I didn’t want to paint the MessageBox window myself and I wanted only to change some texts. If you want to paint the main window, I think you shouldn’t call this function!

For more information about SetWindowsHookEx, SetWindowLong and CallWindowProc use MSDN Library. (I think it is the best reference to revert).

And at last I want to warn you: Call the CallNextHookEx () function because if you don’t do this, other applications that may have installed a hook chain will not receive the hook information and I know you don’t want it.

And like always, according to MSDN that says: Calling the CallNextHookEx function to chain to the next hook procedure is optional, but it is highly recommended; otherwise, other applications that have installed hooks will not receive hook notifications and may behave incorrectly as a result. You should call CallNextHookEx unless you absolutely need to prevent the notification from being seen by other applications.

Last Words

First of all, I want to thanks to Mr. Nicolas Bonamy. His article helped me a lot.

There is a demo app which if you want, can download. In that project I have a class that contains some codes for adding a CheckBox to the MessageBox and to change the text of buttons and some functions to place the controls in a right and good place.

And I want to say that my English is not very well and it is a reason to write MSDN Library definitions for some functions (Excuse me for bad grammar).

And at last I suggest you to use Visual Assist X because it is a helpful plug-in for Visual Studio.

Please vote this article if you find it interesting and informative. Opinions and comments are welcome.

G.K.Z - King Zoser.