跟踪栏的win32 C ++自定义颜色thumb

Question

I have spent today searching everywhere for a concrete explanation or example of coloring the thumb on a trackbar (slider) in win32 C++. Everything I've found has been partially explained, and in trying every conceivable variation I have come up blank.

The control I have been focused on is defined in my rc file as CONTROL "",IDC_PLAYSLIDER,"msctls_trackbar32",TBS_NOTICKS | WS_TABSTOP,5,22,187,15

Essentially, my message handling of NM_CUSTOMDRAW comes down to the following. I have no confidence on my color/hdc handling, but the lack of messages is my primary problem.

INT_PTR CALLBACK dialogproc(HWND h, UINT m, WPARAM w, LPARAM l)
{
    switch (m) {
    case WM_NOTIFY:
    {
        switch (((LPNMHDR)l)->code) {
        case NM_CUSTOMDRAW:
        {
            LPNMCUSTOMDRAW lpNMCD = (LPNMCUSTOMDRAW)l;
            UINT idc = lpNMCD->hdr.idFrom;

            switch (lpNMCD->dwDrawStage) {
            case CDDS_PREPAINT:
                return   CDRF_NOTIFYSUBITEMDRAW;
                break;
            case CDDS_SUBITEM | CDDS_ITEMPREPAINT:
            {
                switch (lpNMCD->dwItemSpec)
                {
                case TBCD_THUMB:
                    HGDIOBJ old_pen = SelectObject(lpNMCD->hdc, penSlider);
                    HGDIOBJ old_brush = SelectObject(lpNMCD->hdc, brushSlider);
                    return CDRF_NEWFONT;
                }
            }
            break;
        }

What I am getting at runtime is a CDDS_PREPAINT on the correct control, but no matter what I have tried, I have had no further CDDS_ drawStage messages.

If anyone has done this on a trackbar (most examples are list controls) and is willing to share their message handler code, or can otherwise shed light on my confusion, that would be greatly appreciated.

Answer 1

From the docs for NM_CUSTOMDRAW :

If this message is handled in a dialog procedure, you must set the return value as part of the window data before returning TRUE. For more information, see DialogProc .

The DialogProc docs say:

If the dialog box procedure processes a message that requires a specific return value, the dialog box procedure should set the desired return value by calling SetWindowLong(hwndDlg, DWL_MSGRESULT, lResult) immediately before returning TRUE

Note that with the advent of 64-bit windows it is better practice to use SetWindowLongPtr(hwndDlg, DWLP_MSGRESULT, lResult) .