Question

I was thinking i could use the LVITEM structures LPARAM to attach a pointer to my class, but i can’t seem to get it to work!

Heres the main parts of my code:

Creating the listview:

hlvQuiz = CreateChild(WC_LISTVIEW, "",
    WS_CHILD | WS_VISIBLE | WS_VSCROLL | WS_HSCROLL | LVS_ICON | LVS_AUTOARRANGE,
    0, 0, 320, 240, m_hwnd, FontNormal);

Adding items:

if (vQuizes.size() > 0)
{
    LVITEM lvi;
    lvi.mask = LVIF_TEXT | LVIF_PARAM;
    lvi.iItem = 0;
    lvi.iSubItem = 0;
    lvi.cchTextMax = QUIZSTRLEN;

    for (unsigned int i = 0; i < vQuizes.size(); i++)
    {
        lvi.lParam = (LPARAM)&vQuizes[i]; // adding pointer to lparam
        lvi.pszText = vQuizes[i].szName;
        ListView_InsertItem(hlvQuiz, &lvi);
    }
}

Then later when i go to get my class back from the LPARAM:

        LVITEM lvi;
    lvi.iItem = ListView_GetNextItem(hwnd, -1, LVNI_SELECTED);
    lvi.iSubItem = 0;

    if (ListView_GetItem(fm->hlvQuiz, &lvi) == TRUE)
    {
        Quiz* q = (Quiz*)lvi.lParam;
        if (q != NULL) // i get stopped here because my pointer is NULL
            if (Exists(q->szPath) == IS_FILE)
                ShellExecute(NULL, "edit", q->szPath, NULL, NULL, SW_SHOWNORMAL);
    }

Is there anything that i’m doing wrong? the listview creates fine, and the items add, but the pointer to my class which i put in the LPARAM value seems to be ignored, or changed by the time i come to dereference it

Answer 1

I haven’t worked at this low level before, but I suspect you need to set the mask member of the LVITEM structure to LVIF_PARAM (as well as the appropriate values for anything else you need) for the call to ListView_GetItem.