如何在拖放文件至CDialogEx的CEdit控件时显示插入符光标？

Absolutely, this is totally doable and will make your drag-and-drop workflow way more user-friendly—users will instantly see exactly where their file path will land. Let’s break down how to implement this step by step:

Step 1: Subclass CEdit to Handle Drag Hover Events #

First, we need to create a custom CEdit subclass because the default control doesn’t natively handle updating the caret position during drag-over. This lets us take control of when and where the caret appears as the user drags a file over the edit box.

Here’s the header for your subclass:

class CDropEdit : public CEdit
{
protected:
    DECLARE_MESSAGE_MAP()
    afx_msg void OnDragEnter(HDROP hDropInfo);
    afx_msg void OnDragOver(HDROP hDropInfo, DWORD dwKeyState, POINT pt);
};

And the implementation:

BEGIN_MESSAGE_MAP(CDropEdit, CEdit)
    ON_WM_DRAGENTER()
    ON_WM_DRAGOVER()
END_MESSAGE_MAP()

void CDropEdit::OnDragEnter(HDROP hDropInfo)
{
    // Grab focus immediately so the caret becomes visible
    SetFocus();

    // Convert the drag position from screen to client coordinates
    POINT screenPt;
    DragQueryPoint(hDropInfo, &screenPt);
    ScreenToClient(&screenPt);

    // Find the exact character position under the mouse
    int charPos = CharFromPos(screenPt);
    int insertPos = LOWORD(charPos);

    // Set the caret to this position and ensure it's visible
    SetSel(insertPos, insertPos);
    ShowCaret();

    // Tell the system we accept this drag operation
    DragAcceptFiles(TRUE);
}

void CDropEdit::OnDragOver(HDROP hDropInfo, DWORD dwKeyState, POINT pt)
{
    // Update the caret position as the user moves the mouse over the edit box
    POINT clientPt = pt;
    ScreenToClient(&clientPt);

    int charPos = CharFromPos(clientPt);
    int insertPos = LOWORD(charPos);

    SetSel(insertPos, insertPos);
    ShowCaret();

    // Indicate we accept a copy operation (adjust to DROPEFFECT_MOVE if needed)
    SetDropEffect(DROPEFFECT_COPY);
}

Step 2: Link the Subclass to Your Dialog’s CEdit Control #

In your dialog class (CWeekendMeetingDlg), replace the default CEdit member with your new CDropEdit subclass:

In your dialog header:

CDropEdit m_editDropTarget; // Replace your original CEdit declaration

Then, update your DoDataExchange method to associate the subclass with the control ID:

void CWeekendMeetingDlg::DoDataExchange(CDataExchange* pDX)
{
    CDialogEx::DoDataExchange(pDX);
    DDX_Control(pDX, IDC_YOUR_EDIT_CONTROL_ID, m_editDropTarget); // Replace with your actual control ID
}

Step 3: Update OnDropFiles to Insert at the Caret Position #

Modify your existing OnDropFiles handler to insert the file path exactly where the caret is positioned:

void CWeekendMeetingDlg::OnDropFiles(HDROP hDropInfo)
{
    // Check if the drop target is our custom edit control
    CWnd* pFocusedWnd = GetFocus();
    if (pFocusedWnd == &m_editDropTarget)
    {
        TCHAR szFilePath[MAX_PATH] = {0};
        // Get the first dropped file (loop this to handle multiple files)
        if (DragQueryFile(hDropInfo, 0, szFilePath, MAX_PATH))
        {
            int insertPos = m_editDropTarget.GetSelStart();
            // Insert the file path at the current caret position
            m_editDropTarget.SetSel(insertPos, insertPos);
            m_editDropTarget.ReplaceSel(szFilePath);
        }
    }

    // Optional: Call base class if you need default handling for other drop targets
    // __super::OnDropFiles(hDropInfo);
}

Step 4: Enable Drag Acceptance #

Make sure you enable drag-and-drop for your dialog in OnInitDialog:

BOOL CWeekendMeetingDlg::OnInitDialog()
{
    CDialogEx::OnInitDialog();

    // Enable the dialog to accept dropped files
    DragAcceptFiles(TRUE);

    // ... rest of your OnInitDialog code ...

    return TRUE;
}

Bonus Tips #

• Handle Multiple Files: Loop DragQueryFile until it returns 0 to process all dropped files, inserting each path sequentially.
• Clean Up on Drag Leave: Add a OnDragLeave handler to hide the caret if needed, though the system usually handles this when focus is lost.
• Customize Drop Effects: Adjust SetDropEffect to match your app’s behavior (e.g., DROPEFFECT_MOVE if you want to move files instead of copying paths).

内容的提问来源于stack exchange，提问作者Andrew Truckle