Make a child window from DLL

Hi guys I'm new here,
I am trying to make a DLL so that I call a certain function in that DLL, it will create a child window for the current program from where I call that function(this is going to be called on a different language).


I got it to work, but the problem is after the child window pop up, after a server seconds it disappears, but when I hover the area where it used to be parts of the child window appear, meaning it is there but has become invisible somehow.

Let me know if there's a way to fix this.
Much appreciated.

I will also add my code(btw I got the code from this forum)

Code:

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#include "stdafx.h"
#include <mmsystem.h>


HWND window = NULL;
LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
LRESULT CALLBACK HelloWndProc(HWND, UINT, WPARAM, LPARAM);






_DLLAPI int __stdcall CreateWin(HWND hwnd)
{
    HINSTANCE hInstance = (HINSTANCE)hwnd;
    static TCHAR szAppName2[] = TEXT("SineApplication");
    HWND hwnd2;
    MSG msg;
    WNDCLASS mywndclass;






    mywndclass.style = CS_HREDRAW | CS_VREDRAW;
    mywndclass.lpfnWndProc = WndProc;
    mywndclass.cbClsExtra = 0;
    mywndclass.cbWndExtra = sizeof(long);
    mywndclass.hInstance = hInstance;
    mywndclass.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    mywndclass.hCursor = LoadCursor(NULL, IDC_ARROW);
    mywndclass.hbrBackground = (HBRUSH)GetStockObject(WHITE_BRUSH);
    mywndclass.lpszMenuName = NULL;
    mywndclass.lpszClassName = szAppName2;


    if (!RegisterClass(&mywndclass))
    {
        MessageBox(NULL, TEXT("Not Working"),
            szAppName2, MB_ICONERROR);
        return 0;
    }




    hwnd2 = CreateWindow(szAppName2,
        TEXT("Hello World"),
        WS_CHILD | WS_VISIBLE | WS_CAPTION
        | WS_SYSMENU | WS_THICKFRAME
        | WS_MINIMIZEBOX | WS_MAXIMIZEBOX | WS_CLIPSIBLINGS,
        CW_USEDEFAULT,
        CW_USEDEFAULT,
        300,
        300,
        hwnd,
        NULL,
        hInstance,
        NULL);


    SetParent(hwnd2, hwnd);
    ShowWindow(hwnd2, SW_SHOW);
    UpdateWindow(hwnd2);


    while (GetMessage(&msg, NULL, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }


    return msg.wParam;
}








LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    HDC    hdc;
    PAINTSTRUCT ps;
    RECT    rect;


    switch (message) {
    case WM_CREATE:
        return 0;


    case WM_PAINT:
        hdc = BeginPaint(hwnd, &ps);


        GetClientRect(hwnd, &rect);


        DrawText(hdc, TEXT("Welcome to child window"), -1, &rect,
            DT_SINGLELINE | DT_CENTER | DT_VCENTER);


        EndPaint(hwnd, &ps);
        return 0;


    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }


    return DefWindowProc(hwnd, message, wParam, lParam);
}

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Code:

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HINSTANCE hInstance = (HINSTANCE)hwnd;

---

A HINSTANCE isn't a HWND. That looks like a very suspect construct to me.

It looks like you are trying to create a 'Custom Control'. A Custom Control is a child window of a parent. There are very specific ways of going about this.

Here's a link to a tutorial of mine on this topic (Custom Controls)....

Fred's Tutorial #10: Building A Custom Control - A Simple Example

The coding is in PowerBASIC but that doesn't matter (much). I have this in C++ somewhere, but I'd have to hunt it up.

A much better architecture for you to consider, is a registration function in the dll called from the host during the host's WM_CREATE processing. Then the CreateWindow() call for the child window control is in the host - not the server/client.

Another point to consider is that the client should be able to create multiple instances of the child window control (custom control - that's what RegisterClassEx() gives you - a custom window/contol). For this reason statics or globals are strictly verboten.