c++ - 拖放 Win API 32

Question

我正在尝试将一个 ListView 项目从我的程序拖放到另一个项目(就像将路径拖到 VLC 中的某处，它会播放视频文件)。我正在使用 CF_HDROP 剪贴板格式。 CopySelection 将 STGMEDIUM hglobal 变量设置为 DROPFILES 结构。

void CopySelection(HWND hwndList, STGMEDIUM &stgmed)
{
    HGLOBAL hMem;
    DROPFILES  *ptr;
    DROPFILES dfiles;
    POINT p;

    // get the selection inside the list control
    int iPos = SendMessage(hwndList, LVM_GETNEXTITEM, (WPARAM)-1,(LPARAM)LVNI_SELECTED);
    cout << "iPos: " << iPos << endl;
    LVITEM item;
    char buffer[256];
    string fileDir = "";
    item.iItem = iPos;
    item.iSubItem = 1;
    item.cchTextMax = 256;
    item.pszText = buffer;
    item.mask = LVIF_TEXT;

    ListView_GetItem(hwndList, &item);
    fileDir += string(item.pszText);
    fileDir += "\\";
    item.iItem = iPos;
    item.iSubItem = 0;

    ListView_GetItem(hwndList, &item);
    fileDir += string(item.pszText);
    item.iItem = iPos;
    item.iSubItem = 2;

    ListView_GetItem(hwndList, &item);
    fileDir += string(item.pszText);

    cout << "fileDir: " << fileDir << endl;

    hMem = GlobalAlloc(GHND, sizeof(DROPFILES));
    ptr  = (DROPFILES *)GlobalLock(hMem);

    dfiles.fNC = TRUE;
    dfiles.fWide = FALSE;
    memcpy((void*)&dfiles.pFiles, (fileDir.c_str()+'\0'), fileDir.size()+1);

    GetCursorPos(&p);
    dfiles.pt=p;

    // copy the selected text and nul-terminate
    memcpy(ptr, (void*)&dfiles, sizeof(DROPFILES));

    GlobalUnlock(hMem);

    stgmed.hGlobal = hMem;

    //return hMem;
}

但这似乎会导致段错误。下面是调用它的 MouseMove 列表消息代码:

case WM_MOUSEMOVE:
{
    // stop drag-drop from happening when the mouse is released.
    if(fMouseDown)
    {
        IDataObject *pDataObject;
        IDropSource *pDropSource;
        DWORD        dwEffect;
        DWORD        dwResult;

        FORMATETC fmtetc = { CF_HDROP, 0, DVASPECT_CONTENT, -1, TYMED_HGLOBAL };
        STGMEDIUM stgmed = { TYMED_HGLOBAL   , { 0 }, 0 };

        // transfer the current selection into the IDataObject
        CopySelection(hwnd, stgmed);
        cout << "DO WE?" << endl;

        // Create IDataObject and IDropSource COM objects
        CreateDropSource(&pDropSource);
        CreateDataObject(&fmtetc, &stgmed, 1, &pDataObject);
        //
        //  ** ** ** The drag-drop operation starts here! ** ** **
        //
        //dwResult = DoDragDrop(pDataObject, pDropSource, DROPEFFECT_COPY|DROPEFFECT_MOVE, &dwEffect);
        dwResult = DoDragDrop(pDataObject, pDropSource, DROPEFFECT_COPY, &dwEffect);

        // success!
        if(dwResult == DRAGDROP_S_DROP)
        {
            if(dwEffect & DROPEFFECT_MOVE)
            {
                // remove selection from list control
            }
            else if(dwEffect & DROPEFFECT_LINK)
            {
            }
        }
        // cancelled
        else if(dwResult == DRAGDROP_S_CANCEL)
        {
        }

        pDataObject->Release();
        pDropSource->Release();

        ReleaseCapture();
        fMouseDown = FALSE;
        fDidDragDrop = TRUE;
    }

代码格式正确(我已经检查过)但不确定为什么这不起作用。我什至使用正确的 OLE 剪贴板格式来实现这一点吗？我不确定该使用哪个，而且我找到的文档也不是很好。

干杯， 罗布

附言我试图改编这个例子: http://www.catch22.net/tuts/drop-source

不同的是，他只是移动文本，而我试图移动文件列表(比如在窗口中选择图标并拖到视频播放器上)。

Answer 1

您没有为 HGLOBAL block 分配足够的内存。您只分配足够的内存来保存 DROPFILES 本身，但没有内存来保存它附带的文件名。但是，即使您正确分配了内存，您也没有正确使用 DROPFILES::pFiles 字段。它需要指定从文件名列表开始的 DROPFILES 结构开始处的偏移量，但您将其视为内存地址。

试试这个:

HGLOBAL CopySelection(HWND hwndList)
{
    // get the selection inside the list control

    int iPos = SendMessage(hwndList, LVM_GETNEXTITEM, (WPARAM)-1,(LPARAM)LVNI_SELECTED);
    if (iPos == -1)
        return NULL;

    cout << "iPos: " << iPos << endl;

    LVITEM item = {0};
    char buffer[256];
    string fileDir;

    item.cchTextMax = 256;
    item.pszText = buffer;
    item.mask = LVIF_TEXT;

    item.iItem = iPos;
    item.iSubItem = 1;
    ListView_GetItem(hwndList, &item);
    fileDir = item.pszText;
    fileDir += "\\";

    item.iItem = iPos;
    item.iSubItem = 0;
    ListView_GetItem(hwndList, &item);
    fileDir += item.pszText;

    item.iItem = iPos;
    item.iSubItem = 2;
    ListView_GetItem(hwndList, &item);
    fileDir += item.pszText;

    cout << "fileDir: " << fileDir << endl;

    // +2 = the filename's null terminator and the file list's null terminator
    HGLOBAL hMem = GlobalAlloc(GHND, sizeof(DROPFILES) + fileDir.length() + 2);
    if (!hMem)
        return NULL;

    DROPFILES *dfiles = (DROPFILES*) GlobalLock(hMem);
    if (!dfiles)
    {
        GlobalFree(hMem);
        return NULL;
    }

    dfiles->pFiles = sizeof(DROPFILES);
    GetCursorPos(&(dfiles->pt));
    dfiles->fNC = TRUE;
    dfiles->fWide = FALSE;
    memcpy(&dfiles[1], fileDir.c_str(), fileDir.length());

    GlobalUnlock(hMem);
    return hMem;
}

.

case WM_MOUSEMOVE:
{
    // stop drag-drop from happening when the mouse is released.
    if (fMouseDown)
    {
        IDataObject *pDataObject;
        IDropSource *pDropSource;
        DWORD        dwEffect;
        DWORD        dwResult;

        FORMATETC fmtetc = { CF_HDROP, 0, DVASPECT_CONTENT, -1, TYMED_HGLOBAL };
        STGMEDIUM stgmed = { TYMED_HGLOBAL   , { 0 }, 0 };

        // transfer the current selection into the IDataObject
        stgmed.hGlobal = CopySelection(hwnd);
        if (stgmed.hGlobal)
        {
            cout << "DO WE?" << endl;

            // Create IDataObject and IDropSource COM objects
            CreateDropSource(&pDropSource);
            CreateDataObject(&fmtetc, &stgmed, 1, &pDataObject);
            //
            //  ** ** ** The drag-drop operation starts here! ** ** **
            //
            //dwResult = DoDragDrop(pDataObject, pDropSource, DROPEFFECT_COPY|DROPEFFECT_MOVE, &dwEffect);
            dwResult = DoDragDrop(pDataObject, pDropSource, DROPEFFECT_COPY, &dwEffect);

            // success!
            if(dwResult == DRAGDROP_S_DROP)
            {
                if(dwEffect & DROPEFFECT_MOVE)
                {
                    // remove selection from list control
                }
                else if(dwEffect & DROPEFFECT_LINK)
                {
                }
            }
            // cancelled
            else if(dwResult == DRAGDROP_S_CANCEL)
            {
            }

            pDataObject->Release();
            pDropSource->Release();

            ReleaseCapture();
            fMouseDown = FALSE;
            fDidDragDrop = TRUE;
        }
    }

如果你想一次拖动多个选定的文件，试试这个:

HGLOBAL CopySelection(HWND hwndList)
{
    vector<string> files;
    UINT len = 0;

    // get the selection inside the list control

    int iPos = -1;
    do
    {
        int iPos = SendMessage(hwndList, LVM_GETNEXTITEM, iPos, LVNI_SELECTED);
        if (iPos == -1)
            break;

        LVITEM item = {0};
        char buffer[256];
        string fileDir;

        item.cchTextMax = 256;
        item.pszText = buffer;
        item.mask = LVIF_TEXT;

        item.iItem = iPos;
        item.iSubItem = 1;
        ListView_GetItem(hwndList, &item);
        fileDir = item.pszText;
        fileDir += "\\";

        item.iItem = iPos;
        item.iSubItem = 0;
        ListView_GetItem(hwndList, &item);
        fileDir += item.pszText;

        item.iItem = iPos;
        item.iSubItem = 2;
        ListView_GetItem(hwndList, &item);
        fileDir += item.pszText;

        files.push_back(fileDir);

        // +1 = the filename's null terminator
        len += (fileDir.length() + 1);

        cout << "iPos: " << iPos << ", fileDir: " << fileDir << endl;
    }
    while (true);

    if (files.empty())
        return NULL;

    // +1 = the file list's null terminator
    HGLOBAL hMem = GlobalAlloc(GHND, sizeof(DROPFILES) + len + 1);
    if (!hMem)
        return NULL;

    DROPFILES *dfiles = (DROPFILES*) GlobalLock(hMem);
    if (!dfiles)
    {
        GlobalFree(hMem);
        return NULL;
    }

    dfiles->pFiles = sizeof(DROPFILES);
    GetCursorPos(&(dfiles->pt));
    dfiles->fNC = TRUE;
    dfiles->fWide = FALSE;

    char *pFile = (char*) &dfiles[1];
    for (vector<string>::size_type i = 0; i < files.size(); ++i)
    {
        string &fileDir = files[i];

        // +1 = the filename's null terminator
        len = (fileDir.length() + 1);

        memcpy(pFile, fileDir.c_str(), len);
        pFile += len;
    }

    GlobalUnlock(hMem);
    return hMem;
}