IDropTarget を実装する

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参考リンク:
IDropTargetを実装する
7.IDropTargetとOLEドラッグ&ドロップ - COM研究室

まずは定型

#include <shlobj.h>

class TDropTargetBase : public IDropTarget
{
protected:
    unsigned int refCount;

    TDropTargetBase();
    ~TDropTargetBase();

    virtual HRESULT __stdcall QueryInterface(const IID& iid, void** ppv);
    virtual ULONG __stdcall AddRef();
    virtual ULONG __stdcall Release();

};

TDropTargetBase::TDropTargetBase() {
    refCount = 0;
};

TDropTargetBase::~TDropTargetBase() {
};

HRESULT TDropTargetBase::QueryInterface(const IID& iid, void** ppv){
    if (IsEqualIID(iid, IID_IUnknown) || IsEqualIID(iid, IID_IDropTarget))
        *ppv = static_cast<IDropTarget *>(this);
    else
    {
        *ppv = NULL;
        return E_NOINTERFACE;
    }

    AddRef();

    return S_OK;
}

ULONG TDropTargetBase::AddRef(){
    refCount++;
    return refCount;
}

ULONG TDropTargetBase::Release(){
    refCount--;
    if (refCount == 0) {
        delete this;
    }
    return refCount;
}

IDropTarget::DragEnter, DragOver, DragLeave, Drop を実装する。

//  TDropTargetBase は、この説明で定型の部分を分離したかっただけで、本当はクラス分けする必要性は皆無。

class TDropTarget : public TDropTargetBase
{
public:
    static void CreateInstance(IDropTarget **);
private:
    virtual HRESULT __stdcall DragEnter(IDataObject* pDataObj, DWORD grfKeyState, POINTL pt, DWORD* pdwEffect);
    virtual HRESULT __stdcall DragOver(DWORD grfKeyState, POINTL pt, DWORD* pdwEffect);
    virtual HRESULT __stdcall DragLeave();
    virtual HRESULT __stdcall Drop(IDataObject* pDataObj, DWORD grfKeyState, POINTL pt, DWORD* pdwEffect);
};

void TDropTarget::CreateInstance(IDropTarget **pp) {
    if (pp != NULL) {
        TDropTarget *p = new TDropTarget();
        p->QueryInterface(IID_IDropTarget, (void **)pp);
    }
}

#include <tchar.h>
#include <string>
typedef std::basic_string<TCHAR> tstring;

static void OutputDebugEffectString(DWORD *pdwEffect) {
    tstring sz;
    sz += TEXT("DROPEFFECT_");
    if (*pdwEffect == DROPEFFECT_NONE) {
        sz += TEXT("NONE");
    }
    else {
        if (*pdwEffect & DROPEFFECT_COPY) {
            sz += TEXT("COPY/");
        }
        if (*pdwEffect & DROPEFFECT_MOVE) {
            sz += TEXT("MOVE/");
        }
        if (*pdwEffect & DROPEFFECT_LINK) {
            sz += TEXT("LINK/");
        }
        if (*pdwEffect & DROPEFFECT_LINK) {
            sz += TEXT("SCROLL/");
        }
        sz.pop_back();
    }

    OutputDebugString(sz.data());
}

HRESULT TDropTarget::DragEnter(IDataObject* pDataObj, DWORD grfKeyState, POINTL pt, DWORD* pdwEffect){
    OutputDebugString(TEXT("DragOver"));
    OutputDebugEffectString(pdwEffect);
    OutputDebugString(TEXT("\r\n"));
    return S_OK;
}

HRESULT TDropTarget::DragOver(DWORD keyState, POINTL pt, DWORD* effect){
    OutputDebugString(TEXT("DragOver"));
    OutputDebugString(TEXT("\r\n"));
    return S_OK;
}

HRESULT TDropTarget::DragLeave(){
    OutputDebugString(TEXT("DragLeave"));
    OutputDebugString(TEXT("\r\n"));
    return S_OK;
}

HRESULT TDropTarget::Drop(IDataObject* pDataObj, DWORD grfKeyState, POINTL pt, DWORD* pdwEffect){
    OutputDebugString(TEXT("Drop"));
    OutputDebugEffectString(pdwEffect);
    OutputDebugString(TEXT("\r\n"));
    return S_OK;
}

ウィンドウに割り当てる。

(ウィンドウプロシージャ内部)
    case WM_CREATE:
        ...
        {
            IDropTarget *pDropTarget;
            TDropTarget::CreateInstance(&pDropTarget);
            RegisterDragDrop(hwnd, pDropTarget);    // OLE機能にIDropTargetを登録
            pDropTarget->Release();
        }
        ...
        break;
    case WM_CLOSE:
        ...
        RevokeDragDrop(hwnd);
        ...
        break;

この時点で、もうファイルやテキストのドロップなどができる状態。

DragEnter, Drop をちゃんと実装する。

HRESULT TDropTarget::DragEnter(IDataObject* pDataObj, DWORD grfKeyState, POINTL pt, DWORD* pdwEffect){
    HRESULT    hr;
    FORMATETC  formatetc;

    // ドロップされようとしてるデータが CF_HDROP フォーマットをサポートしているかどうかを調べる
    formatetc.cfFormat = CF_HDROP;
    formatetc.ptd      = NULL;
    formatetc.dwAspect = DVASPECT_CONTENT;
    formatetc.lindex   = -1;
    formatetc.tymed    = TYMED_HGLOBAL;

    hr = pDataObj->QueryGetData(&formatetc);
    if(hr != S_OK){
        *pdwEffect = DROPEFFECT_NONE;
    }else{
        *pdwEffect = DROPEFFECT_COPY;
    }

    return (*pdwEffect == DROPEFFECT_NONE) ? DRAGDROP_S_CANCEL:
        S_OK;
    // ちゃんと DRAGDROP_S_CANCEL を返してやらないと、DROPEFFECT_NONE にも関わらず
    // Drop できてしまう。
}


static HRESULT GetDroppedFiles(IDataObject *pDataObj, std::list<tstring> *pDroppedFiles) {
    HRESULT hr;

    FORMATETC  formatetc;
    formatetc.cfFormat = CF_HDROP;
    formatetc.ptd      = NULL;
    formatetc.dwAspect = DVASPECT_CONTENT;
    formatetc.lindex   = -1;
    formatetc.tymed    = TYMED_HGLOBAL;

    hr = pDataObj->QueryGetData(&formatetc);
    if (FAILED(hr)) {
        goto fail;
    }

    STGMEDIUM medium;
    hr = pDataObj->GetData(&formatetc, &medium);
    if (FAILED(hr)) {
        goto fail;
    }

    HDROP p = (HDROP)GlobalLock(medium.hGlobal);

    int num = DragQueryFile(p, 0xFFFFFFFF, NULL, 0);
    for (int iFile = 0; iFile < num; iFile++) {
        int size = DragQueryFile(p, iFile, NULL, 0);

        TCHAR * buf = new TCHAR[size + 1];

        // assert(size == 
            DragQueryFile(p, iFile, buf, size + 1)
        // )
            ;

        pDroppedFiles->push_back(tstring(buf));
        delete[] buf;
    }

    GlobalUnlock(medium.hGlobal);
    ReleaseStgMedium(&medium);
fail:
    return hr;
}

HRESULT TDropTarget::Drop(IDataObject* pDataObj, DWORD /*grfKeyState*/, POINTL /*pt*/, DWORD* pdwEffect) {
    HRESULT rc;

    OutputDebugString(TEXT("Drop : "));
    OutputDebugEffectString(pdwEffect);
    OutputDebugString(TEXT("\r\n"));

    std::list<tstring> droppedFiles;

    HRESULT hr = GetDroppedFiles(pDataObj, &droppedFiles);
    if (SUCCEEDED(hr) == false)
    {
        goto fail;
    }
    else
    {
        tstring debugString;

        for(std::list<tstring>::iterator ite = droppedFiles.begin();
            ite != droppedFiles.end();
            ite++) 
        {
            debugString += *ite;
            debugString += TEXT("\r\n");
        }

        OutputDebugString(debugString.data());
    }

    rc = S_OK;
    goto cleanUp;
fail:
    rc = E_FAIL;
    OutputDebugString(TEXT("Something wrong."));
cleanUp:
    return rc;
}