MFC 无边框窗体实现用鼠标拖动窗体边缘实现窗体大小变化

你可以重载MFC窗体类的`OnNcHitTest`函数，该函数用于处理非客户区的鼠标消息。具体实现如下：

UINT CMyWnd::OnNcHitTest(CPoint point)
{
    UINT nHitTest = CWnd::OnNcHitTest(point);

    // 如果鼠标在窗口边缘，设置对应的nHitTest值
    CRect rc;
    GetWindowRect(&rc);
    if (point.x >= rc.left && point.x <= rc.left + m_nBorderWidth)
    {
        if (point.y >= rc.top && point.y <= rc.top + m_nBorderWidth)
            nHitTest = HTTOPLEFT;           // 左上角
        else if (point.y >= rc.bottom - m_nBorderWidth && point.y <= rc.bottom)
            nHitTest = HTBOTTOMLEFT;        // 左下角
        else
            nHitTest = HTLEFT;              // 左侧
    }
    else if (point.x >= rc.right - m_nBorderWidth && point.x <= rc.right)
    {
        if (point.y >= rc.top && point.y <= rc.top + m_nBorderWidth)
            nHitTest = HTTOPRIGHT;          // 右上角
        else if (point.y >= rc.bottom - m_nBorderWidth && point.y <= rc.bottom)
            nHitTest = HTBOTTOMRIGHT;       // 右下角
        else
            nHitTest = HTRIGHT;             // 右侧
    }
    else if (point.y >= rc.top && point.y <= rc.top + m_nBorderWidth)
    {
        nHitTest = HTTOP;                   // 顶部
    }
    else if (point.y >= rc.bottom - m_nBorderWidth && point.y <= rc.bottom)
    {
        nHitTest = HTBOTTOM;                // 底部
    }

    return nHitTest;
}

然后你可以在窗体的`OnNcLButtonDown`和`OnMouseMove`消息中处理鼠标拖动事件，具体实现如下：

void CMyWnd::OnNcLButtonDown(UINT nHitTest, CPoint point)
{
    if (nHitTest == HTTOP || nHitTest == HTBOTTOM || nHitTest == HTLEFT || 
        nHitTest == HTRIGHT || nHitTest == HTTOPLEFT || nHitTest == HTTOPRIGHT || 
        nHitTest == HTBOTTOMLEFT || nHitTest == HTBOTTOMRIGHT)
    {
        // 设置捕获鼠标
        SetCapture();

        // 获取当前窗口大小和鼠标位置
        GetWindowRect(&m_rcWnd);
        GetCursorPos(&m_ptCursor);

        // 记录当前窗口大小和鼠标位置
        m_nHitTest = nHitTest;
        m_nWidth = m_rcWnd.Width();
        m_nHeight = m_rcWnd.Height();
        m_ptLast = m_ptCursor;
    }
    else
    {
        CWnd::OnNcLButtonDown(nHitTest, point);
    }
}

void CMyWnd::OnMouseMove(UINT nFlags, CPoint point)
{
    if (GetCapture() == this)
    {
        // 获取鼠标位置
        GetCursorPos(&m_ptCursor);

        // 计算窗口大小和位置
        int dx = m_ptCursor.x - m_ptLast.x;
        int dy = m_ptCursor.y - m_ptLast.y;
        CRect rcNew = m_rcWnd;
        switch (m_nHitTest)
        {
        case HTTOP:
            rcNew.top += dy;
            break;
        case HTBOTTOM:
            rcNew.bottom += dy;
            break;
        case HTLEFT:
            rcNew.left += dx;
            break;
        case HTRIGHT:
            rcNew.right += dx;
            break;
        case HTTOPLEFT:
            rcNew.left += dx;
            rcNew.top += dy;
            break;
        case HTTOPRIGHT:
            rcNew.right += dx;
            rcNew.top += dy;
            break;
        case HTBOTTOMLEFT:
            rcNew.left += dx;
            rcNew.bottom += dy;
            break;
        case HTBOTTOMRIGHT:
            rcNew.right += dx;
            rcNew.bottom += dy;
            break;
        }

        // 限制窗口最小大小为100x100
        int nWidth = max(rcNew.Width(), 100);
        int nHeight = max(rcNew.Height(), 100);

        // 设置窗口大小和位置
        SetWindowPos(NULL, rcNew.left, rcNew.top, nWidth, nHeight, SWP_NOZORDER);

        m_ptLast = m_ptCursor;
    }
    else
    {
        CWnd::OnMouseMove(nFlags, point);
    }
}

这样就可以通过鼠标拖动窗口边缘来改变窗口大小了。