c++ - 当用户将 ListView 项目拖到其滚动条上时，执行默认滚动行为

Question

简介:

我的母语不是英语，也不是很有经验的程序员。

我遇到了一个很难描述的问题，所以在阅读这个问题时请牢记这一点。

相关信息:

我正致力于在 ListView 中实现拖放功能。我只想能够在 ListView 中重新排列行，不会将项目拖到其他窗口。

我不想使用 OLE 来执行此操作，而且我对在许多链接上找到的“默认”实现不满意。

我对如何执行此操作有自己的想法，但我的经验不足使我无法实现我的想法。

我正在使用 Visual Studio、C++ 和原始 WinAPI 进行开发。我没有使用任何库，也不想现在就开始使用它们。

问题:

我希望实现以下行为:

用户按下鼠标左键并开始拖动项目 -> 用户将鼠标移到垂直滚动条上 -> 发生默认滚动。

由于滚动条算作非客户区，这意味着我必须以某种方式为 WM_NCMOUSEMOVE 和 WM_NCLBUTTONDOWN 执行默认行为，但我不知道该怎么做。

让我试着更好地解释一下我的意思:

当您拖动项目时，应用程序指示当鼠标悬停在项目上(在 ListView 的客户区中)时项目将被放置的位置是合乎逻辑的。

当您将项目拖到滚动条上时，很明显用户不能将项目放在那里。而不是指示无效的放置点(通过更改光标，例如，像 OLE 那样)，我希望执行以下操作:

我希望执行默认的滚动条行为(就好像用户根本不拖动项目一样)。就好像用户将鼠标悬停在滚动条上，按下并按住鼠标左键，并可选择向上或向下移动鼠标。

当用户将鼠标从滚动条移回 ListView 的客户区时，拖放继续。

中南合作商会

我的英语不够好，无法进行适当的研究(就像我通常在发帖之前所做的那样)，而且我不知道有任何应用程序有这种行为，所以我真的很难尝试解决这是我自己的。

不过，在浏览 Raymond Chen 的博客时，我想到了一个主意。

下面的示例代码完美地演示了我上面谈到的行为。它并不完美，但它最接近实现我想要的行为。

创建空的 C++ 项目并简单地复制/粘贴下面的代码。

然后尝试将项目拖动到滚动条上。

重要提示:我没有实现项目的重新排列，也没有改变光标形状以保持代码最少。此 SSCCE 的目的是展示我想要的行为。

#include <windows.h>
#include <windowsx.h>   // various listview macros etc
#include <CommCtrl.h>
#include <stdio.h>      // swprintf_s()

// enable Visual Styles
#pragma comment( linker, "/manifestdependency:\"type='win32' \
                         name='Microsoft.Windows.Common-Controls' version='6.0.0.0' \
                         processorArchitecture='*' publicKeyToken='6595b64144ccf1df' \
                         language='*'\"")

// link with Common Controls library
#pragma comment( lib, "comctl32.lib")

//global variables
HINSTANCE hInst;
BOOL g_bDrag;

// subclass procedure for listview -> implements drag and drop
LRESULT CALLBACK DragAndDrop(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam,
    UINT_PTR uIdSubclass, DWORD_PTR dwRefData)
{
    switch (message)
    {
    case WM_CAPTURECHANGED:  // in case user ALT+TAB to another window, for example
    {
        g_bDrag = FALSE;
    }
        return DefSubclassProc(hwnd, message, wParam, lParam);

    case WM_LBUTTONUP:      // do the drop ->omitted for brewity
    {
        if (g_bDrag)
        {
            POINT pt = { 0 };
            pt.x = GET_X_LPARAM(lParam);
            pt.y = GET_Y_LPARAM(lParam);

            g_bDrag = FALSE;
            ReleaseCapture();
        }
    }
        return DefSubclassProc(hwnd, message, wParam, lParam);

    case WM_MOUSEMOVE:
    {
        if (g_bDrag)
        {
            POINT pt = { 0 };
            pt.x = GET_X_LPARAM(lParam);
            pt.y = GET_Y_LPARAM(lParam);

            LVHITTESTINFO lvhti = { 0 };
            lvhti.pt = pt;
            ListView_HitTest(hwnd, &lvhti);

            ClientToScreen(hwnd, &pt);  // WM_NCHITTEST takes screen coordinates

            UINT hittest = SendMessage(hwnd, WM_NCHITTEST, 0, MAKELPARAM(pt.x, pt.y));


            if (hittest == HTVSCROLL)  // my try to do the default behavior
            {
                SendMessage(hwnd, WM_NCLBUTTONDOWN, (WPARAM)hittest, (LPARAM)POINTTOPOINTS(pt));
                //SendMessage(hwnd, WM_NCMOUSEMOVE, (WPARAM)hittest, (LPARAM)POINTTOPOINTS(pt));
            }

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

    case WM_NCDESTROY:
        ::RemoveWindowSubclass(hwnd, DragAndDrop, 0);
        return DefSubclassProc(hwnd, message, wParam, lParam);
    }
    return ::DefSubclassProc(hwnd, message, wParam, lParam);
}

// main window procedure
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    switch (msg)
    {
    case WM_CREATE:
    {
        g_bDrag = FALSE;  // user is not dragging listview item

        //================ create an example listview
        RECT rec = { 0 };
        GetClientRect(hwnd, &rec);

        HWND hwndLV = CreateWindowEx(0, WC_LISTVIEW,
            L"", WS_CHILD | WS_VISIBLE | WS_BORDER | LVS_REPORT,
            50, 50, 250, 200, hwnd, (HMENU)2000, hInst, 0);

        // set extended listview styles
        ListView_SetExtendedListViewStyle(hwndLV, LVS_EX_FULLROWSELECT | LVS_EX_GRIDLINES | LVS_EX_DOUBLEBUFFER);

        // add some columns
        LVCOLUMN lvc = { 0 };

        lvc.mask = LVCF_FMT | LVCF_WIDTH | LVCF_TEXT | LVCF_SUBITEM;
        lvc.fmt = LVCFMT_LEFT;

        for (long nIndex = 0; nIndex < 5; nIndex++)
        {
            wchar_t txt[50];
            swprintf_s(txt, 50, L"Column %d", nIndex);

            lvc.iSubItem = nIndex;
            lvc.cx = 60;
            lvc.pszText = txt;

            ListView_InsertColumn(hwndLV, nIndex, &lvc);
        }

        // add some items
        LVITEM lvi;

        lvi.mask = LVIF_TEXT;

        for (lvi.iItem = 0; lvi.iItem < 10000; lvi.iItem++)
        {
            for (long nIndex = 0; nIndex < 5; nIndex++)
            {
                wchar_t txt[50];
                swprintf_s(txt, 50, L"Item %d%d", lvi.iItem, nIndex);

                lvi.iSubItem = nIndex;
                lvi.pszText = txt;
                if (!nIndex)  // item 
                    SendDlgItemMessage(hwnd, 2000, LVM_INSERTITEM, 0, reinterpret_cast<LPARAM>(&lvi));
                else            // sub-item
                    SendDlgItemMessage(hwnd, 2000, LVM_SETITEM, 0, reinterpret_cast<LPARAM>(&lvi));
            }
        }

        //============================ subclass it
        SetWindowSubclass(hwndLV, DragAndDrop, 0, 0);
    }
        return 0L;
    case WM_NOTIFY:
    {
        switch (((LPNMHDR)lParam)->code)
        {
        case LVN_BEGINDRAG:  // user started dragging listview item
        {
            g_bDrag = TRUE;
            SetCapture(((LPNMHDR)lParam)->hwndFrom);  // listview must capture the mouse
        }
            break;
        default:
            break;
        }
    }
        break;
    case WM_CLOSE:
        ::DestroyWindow(hwnd);
        return 0L;
    case WM_DESTROY:
    {
        ::PostQuitMessage(0);
    }
        return 0L;
    default:
        return ::DefWindowProc(hwnd, msg, wParam, lParam);
    }
    return 0;
}

// WinMain

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine,
    int nCmdShow)
{
    // store hInstance in global variable for later use
    hInst = hInstance;

    WNDCLASSEX wc;
    HWND hwnd;
    MSG Msg;

    // register main window class
    wc.cbSize = sizeof(WNDCLASSEX);
    wc.style = 0;
    wc.lpfnWndProc = WndProc;
    wc.cbClsExtra = 0;
    wc.cbWndExtra = 0;
    wc.hInstance = hInst;
    wc.hIcon = LoadIcon(hInstance, IDI_APPLICATION);
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = GetSysColorBrush(COLOR_WINDOW);
    wc.lpszMenuName = NULL;
    wc.lpszClassName = L"Main_Window";
    wc.hIconSm = LoadIcon(hInstance, IDI_APPLICATION);

    if (!RegisterClassEx(&wc))
    {
        MessageBox(NULL, L"Window Registration Failed!", L"Error!", MB_ICONEXCLAMATION |
            MB_OK);

        return 0;
    }

    // initialize common controls
    INITCOMMONCONTROLSEX iccex;
    iccex.dwSize = sizeof(INITCOMMONCONTROLSEX);
    iccex.dwICC = ICC_LISTVIEW_CLASSES;
    InitCommonControlsEx(&iccex);

    // create main window
    hwnd = CreateWindowEx(0, L"Main_Window", L"Listview Drag and Drop",
        WS_OVERLAPPEDWINDOW,
        50, 50, 400, 400, NULL, NULL, hInstance, 0);

    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

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

    return Msg.wParam;
}

现在开始拖动一个项目，然后将鼠标移动到滚动条拇指上方/下方/上方 -> 您观察到的行为就是我要寻找的行为。

这个程序有一个缺陷:

当我尝试将项目拖回 ListView 的客户区时，滚动条仍然受到控制，而不是我的拖动代码。这是默认行为，但我需要以这种方式更改它，以便改为执行我的拖动代码。

这是我自己所能做的最好的。您现在可以看到我正在尝试做什么。

如果需要更多信息，我会更新我的帖子。同时，我会继续自己尝试，如果取得进展，我会更新这篇文章。

感谢您的宝贵时间和帮助。最好的问候。

Answer 1

这种方法工作的唯一方法是找到一种方法来在我们滚动时获取 mouse move 消息。鼠标 “丢失” 但捕获仍然保留到 ListView (滚动条)。因此，当鼠标离开滚动区域时，我们需要释放捕获(从滚动条)并将其再次设置为 ListView 。为此，我们将在收到 LVN_BEGINDRAG 通知消息时应用 WH_MOUSE_LL Hook ，并在完成 拖动 时取消 Hook (这是用于垂直滚动条。这个想法与水平完全相同):

HHOOK mouseHook = NULL;
unsigned char g_bDrag = false, g_bScroll = false; //if we are scrolling
unsigned char g_bVsrollExist = false;
RECT scrollRect; //the scrollbar rectangle, in screen coordinates
int thumbTop, thumbBottom; //the y in screen coordinates
int arrowHeight; //the height of the scrollbar up-down arrow buttons

LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam){
    NMHDR *nmr;

    switch(message){ //handle the messages

        case WM_NOTIFY:
            nmr = (NMHDR *)lParam;

            if( nmr->code == LVN_BEGINDRAG ){
                //printf("BeginDrag \n");

                g_bDrag = true;
                SetCapture(hwndListView);  // listview must capture the mouse
                if( g_bVsrollExist == true ){
                    mouseHook = SetWindowsHookEx(WH_MOUSE_LL, (HOOKPROC)LowLevelMouseProc, NULL, NULL);
                }
            }

        default:   //for messages that we don't deal with
            return DefWindowProc(hwnd, message, wParam, lParam);
    }

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

LRESULT CALLBACK LowLevelMouseProc(int nCode, WPARAM wParam, LPARAM lParam){
    HWND hwnd;
    MSLLHOOKSTRUCT *mslhs;

    if(nCode == HC_ACTION){
        switch( (int)wParam ){ //handle the messages
            case WM_LBUTTONUP:
                //check if we are dragging and release the mouse and unhook
                if( g_bDrag == true ){
                    g_bDrag = false;
                    g_bScroll = false;

                    hwnd = GetCapture();
                    if( hwnd == hwndListView ){
                        ReleaseCapture();
                    }

                    if( mouseHook != NULL ){UnhookWindowsHookEx(mouseHook); mouseHook = NULL;}
                }

                break;               

            case WM_MOUSEMOVE:
                if( g_bDrag == true ){
                    mslhs = (MSLLHOOKSTRUCT *)lParam;

                    // check if we are outside the area which is: scrollbar area minus the arrow buttons
                    if( mslhs->pt.x < scrollRect.left || mslhs->pt.x >= scrollRect.right ||
                    mslhs->pt.y <= scrollRect.top + arrowHeight + 1 || mslhs->pt.y > scrollRect.bottom - arrowHeight - 1 ){

                        if( g_bScroll == true ){
                            //we need to release the capture from scrollbar
                            ReleaseCapture();

                            //set it again to listview
                            SetTimer(hwndListView, 1, 10, NULL);

                            g_bScroll = false;
                        }
                    }
                }

                break;

            default:   //for messages that we don't deal with
                return CallNextHookEx(NULL, nCode, wParam, lParam);
        }
    }

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

在子类 ListView 中:

LRESULT CALLBACK ListViewWndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwrefData){
    POINT pnt;
    SCROLLBARINFO sf;    

    //UNREFERENCED_PARAMETER(uIdSubclass)
    //UNREFERENCED_PARAMETER(dwrefData)

    switch(message){ //handle the messages
        case WM_MOUSEMOVE:
            if( g_bDrag == true && g_bScroll == false && g_bVsrollExist == true ){
                sf.cbSize = sizeof(SCROLLBARINFO);

                GetScrollBarInfo(hwndListView, OBJID_VSCROLL, &sf);

                //in client coordinates
                thumbTop = sf.xyThumbTop;
                thumbBottom = sf.xyThumbBottom;

                //in screen coordinates
                thumbTop += scrollRect.top + 1;
                thumbBottom += scrollRect.top - 2;

                pnt.x = GET_X_LPARAM(lParam);
                pnt.y = GET_Y_LPARAM(lParam);

                ClientToScreen(hwnd, &pnt);

                //we check if we enter the thumb area
                if( pnt.x >= scrollRect.left && pnt.x <= scrollRect.right && 
                    pnt.y > thumbTop + 1 && pnt.y <= thumbBottom - 1 ){
                    g_bScroll = true;
                    SendMessage(hwnd, WM_NCLBUTTONDOWN, (WPARAM)HTVSCROLL, (LPARAM)POINTTOPOINTS(pnt));
                }
            }

            break;

        case WM_TIMER:
            //set the capture to listview to continue getting mouse move messages
            if( (int)wParam == 1 ){
                UpdateWindow(hwndListView);

                SetCapture(hwndListView);

                KillTimer(hwndListView, 1);
            }

            break;

        case WM_LBUTTONDOWN:
            sf.cbSize = sizeof(SCROLLBARINFO);

            GetScrollBarInfo(hwndListView, OBJID_VSCROLL, &sf);

            //check if vertical scrolbar exist
            if( sf.rgstate[0] == STATE_SYSTEM_INVISIBLE ){
                g_bVsrollExist = false;

                break;
            }
            else{g_bVsrollExist = true;}

            arrowHeight = sf.dxyLineButton;
            scrollRect = sf.rcScrollBar;

            //in client coordinates
            thumbTop = sf.xyThumbTop;
            thumbBottom = sf.xyThumbBottom;

            //in screen coordinates
            thumbTop += scrollRect.top + 1;
            thumbBottom += scrollRect.top - 2;

            break;
        case WM_LBUTTONUP:
            if(g_bDrag == true){
                pnt.x = GET_X_LPARAM(lParam);
                pnt.y = GET_Y_LPARAM(lParam);

                g_bDrag = false;
                ReleaseCapture();
            }

            break;

        default:   //for messages that we don't deal with
            return DefSubclassProc(hwnd, message, wParam, lParam);
    }

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

编辑(默认滚动)

unsigned char scrollUp = false, scrollDown = false, scrollLeft = false, 
    scrollRight = false, scrolling = false, vertScrollIsVisible = false, 
    horzScrollIsVisible = false;
int top, down, left, right; //client window in screen coordinates

LRESULT CALLBACK ListViewWndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam, UINT_PTR uIdSubclass, DWORD_PTR dwrefData){
    POINT pnt;
    SCROLLBARINFO sbiVert, sbiHorz;    

    //UNREFERENCED_PARAMETER(uIdSubclass)
    //UNREFERENCED_PARAMETER(dwrefData)

    switch(message){ //handle the messages
        case WM_MOUSEMOVE:
            pnt.x = GET_X_LPARAM(lParam);
            pnt.y = GET_Y_LPARAM(lParam);

            ClientToScreen(hwnd, &pnt);

            if( g_bDrag == true && (horzScrollIsVisible == true || vertScrollIsVisible == true) ){
                CheckMouse(pnt);
            }

            break;

        case WM_LBUTTONDOWN:
            sbiVert.cbSize = sizeof(SCROLLBARINFO);
            sbiHorz.cbSize = sizeof(SCROLLBARINFO);

            GetScrollBarInfo(hwndListView, OBJID_VSCROLL, &sbiVert);
            GetScrollBarInfo(hwndListView, OBJID_HSCROLL, &sbiHorz);

            if( sbiVert.rgstate[0] == STATE_SYSTEM_INVISIBLE ){
                vertScrollIsVisible = false;
            }
            else{
                vertScrollIsVisible = true;
            }

            if( sbiHorz.rgstate[0] == STATE_SYSTEM_INVISIBLE ){
                horzScrollIsVisible = false;
            }
            else{
                horzScrollIsVisible = true;
            }

            if( vertScrollIsVisible == true ){
                //you can get the header handle with hwndHeader = ListView_GetHeader(hwndListView);
                GetWindowRect(hwndHeader, &rt);

                top = rt.bottom;

                GetWindowRect(hwndListView, &rt);

                if( horzScrollIsVisible == true ){
                    bottom = rt.bottom - sbiHorz.dxyLineButton;
                }
                else{
                    bottom = rt.bottom;
                }
            }

            if( horzScrollIsVisible == true ){
                GetWindowRect(hwndListView, &rt);

                left = rt.left;

                if( vertScrollIsVisible == true ){
                    right = rt.right - sbiVert.dxyLineButton;
                }
                else{
                    right = rt.right;
                }
            }

            break;
        case WM_LBUTTONUP:
            if(g_bDrag == true){
                KillTimer(hwndWin, 1); //hwndWin is your main window
                g_bDrag = false;
                ReleaseCapture();
            }

            break;

        default:   //for messages that we don't deal with
            return DefSubclassProc(hwnd, message, wParam, lParam);
    }

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

void CheckMouse(POINT pnt){
    if( pnt.y < top ){
        scrollUp = true;
        scrollDown = false;
    }
    else if( pnt.y >= bottom ){
        scrollDown = true;
        scrollUp = false;
    }
    else{
        scrollUp = false;
        scrollDown = false;
    }

    if( pnt.x >= right ){
        scrollRight = true;
        scrollLeft = false;
    }
    else if( pnt.x < left ){
        scrollLeft = true;
        scrollRight = false;
    }
    else{
        scrollRight = false;
        scrollLeft = false;
    }

    if( scrollUp == true || scrollDown == true || scrollLeft == true || scrollRight == true ){
        if( scrolling == false ){
            scrolling = true;

            SetTimer(hwndWin, 1, 20, NULL);
        }
    }
    else{
        if( scrolling == true ){
            scrolling = false;

            KillTimer(hwndWin, 1);
        }
    }

    return;
}

LRESULT CALLBACK WindowProcedure(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam){
    NMHDR *nmr;

    switch(message){ //handle the messages

        case WM_NOTIFY:
            nmr = (NMHDR *)lParam;

            if( nmr->code == LVN_BEGINDRAG ){
                //printf("BeginDrag \n");

                g_bDrag = true;
                SetCapture(hwndListView);  // listview must capture the mouse
            }

            break;

        case WM_TIMER:
            if( (int)wParam == 1 ){
                if( scrollUp == true && vertScrollIsVisible == true ){
                    SendMessage(hwndListView, WM_VSCROLL, (WPARAM)0x00000000, (LPARAM)0x0); //up
                }

                if( scrollDown == true && vertScrollIsVisible ){
                    SendMessage(hwndListView, WM_VSCROLL, (WPARAM)0x00000001, (LPARAM)0x0); //down
                }

                if( scrollRight == true && horzScrollIsVisible ){
                    SendMessage(hwndListView, WM_HSCROLL, (WPARAM)0x00000001, (LPARAM)0x0); //right
                }

                if( scrollLeft == true && horzScrollIsVisible  ){
                    SendMessage(hwndListView, WM_HSCROLL, (WPARAM)0x00000000, (LPARAM)0x0); //left
                }
            }

            break;

        default:   //for messages that we don't deal with
            return DefWindowProc(hwnd, message, wParam, lParam);
    }

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