Is there any way to change the background color of a messagebox?

For WM_ERASEBKGND, wParam is the required dc. See http://msdn.microsoft.com/en-us/libr...=vs.85%29.aspx

Why do you think that calling SetBkColor() for WM_ERASEBKGND message is going to change the colour of the background? Have you read the article to which I provided a link in post #13?

To change the background colour of a message box as per your original question, try something like this

Code:

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#include <iostream>
#include <Windows.h>
using namespace std;

LRESULT CALLBACK CallWndRetProc(int nCode, WPARAM wParam, LPARAM lParam)
{
PCWPRETSTRUCT prs = (PCWPRETSTRUCT)lParam;
HWND md = FindWindow(NULL, "Caption");

        if ((md != NULL) && (prs->hwnd == md) && (prs->message == WM_ERASEBKGND)) {
                        HBRUSH brush = CreateSolidBrush(RGB(255, 0, 0));
                        RECT rect;
                        GetClientRect(prs->hwnd, &rect);
                        FillRect((HDC)prs->wParam, &rect, brush);
                        DeleteObject(brush);
                        return TRUE;
        }

        return CallNextHookEx(NULL, nCode, wParam, lParam);
}

int main()
{
HHOOK        oldHook = SetWindowsHookEx(WH_CALLWNDPROCRET, CallWndRetProc, NULL, GetCurrentThreadId());

        MessageBox(NULL, "Text", "Caption", MB_OK);

        UnhookWindowsHookEx(oldHook);
}

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I can't help but notice that the code would be far more maintainable if the OP would simply create his own MessageBox or at least use the system colors/themes.

Quote:

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Originally Posted by Arjay

I can't help but notice that the code would be far more maintainable if the OP would simply create his own MessageBox or at least use the system colors/themes.

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True.

Try this (not tested)

Code:

---

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch (uMsg)
    {
        case WM_DESTROY:
                PostQuitMessage(0);
                return 0;

        case WM_ERASEBKGND:               
                        {
                        HBRUSH brush = CreateSolidBrush(RGB(255, 0, 0));
                        RECT rect;
                        GetClientRect(hwnd, &rect);
                        FillRect((HDC)wParam, &rect, brush);
                        DeleteObject(brush);
                        return TRUE;
                        }
        }
        return DefWindowProc(hwnd, uMsg, wParam, lParam);
}

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First note that WM_CTLCOLORMSGBOX message is discontinued and actually has no use.
However, we can customize a dialog box shown with MessageBox or related functions as follows:

1. Before calling MessageBox create a CBT hook.
2. In the hook procedure, catch message box window creation and subclass it (assign an app-defined window procedure).
3. In the app-defined window procedure associated with the message box, handle WM_CTLCOLORDLG (and other messages if needed).
4. Remove the hook procedure when MessageBox exits.

If using MFC, we can override CWinApp::DoMessageBox in order to create a custom message box (based on above steps) when call AfxMessageBox.

See implementation details and demo projects in the following articles:

• Codeguru: Fancy Custom MessageBox
• Codexpert: AfxMessageBox with Auto-close