如何创建所有者绘制的组合框

项目
03/06/2024

本主题演示如何使用所有者绘制的组合框。 C++ 代码示例使用所有者绘制的下拉列表框来显示四个食品组，每个组由位图和名称表示。选择一个食品组会导致该组中的食品出现在列表中。

screen shot showing a dialog box with a list box and an expanded drop-down list box showing an icon and label for each item

该对话框还包含列表框 (IDLIST) 和两个按钮：“确定”(IDOK) 和 “取消”(IDCANCEL)。 IDOK 和 IDCANCEL 常量由 SDK 头文件定义。常量 IDLIST 在应用程序的头文件中定义，控件标识符 IDCOMBO 也是如此。有关对话框的详细信息，请参阅对话框。

需要了解的事项

技术

Windows 控件

先决条件

C/C++
Windows 用户界面编程

说明

步骤 1：创建“所有者绘制”对话框

代码示例使用 DialogBox 函数创建模式对话框。对话框模板 IDD_SQMEAL 定义组合框的窗口样式、按钮和控件标识符。此示例中的组合框使用 CBS_DROPDOWNLIST、CBS_OWNERDRAWFIXED、CBS_SORT、CBS_HASSTRINGS、WS_VSCROLL 和 WS_TABSTOP 样式。

DialogBox(hInst, MAKEINTRESOURCE(IDD_SQMEAL), 
    hWnd, FoodDlgProc);

步骤 2：处理对话框中的 WM_INITDIALOG 和 WM_DESTROY 消息。

在对话框中使用组合框时，通常通过初始化组合框来响应 WM_INITDIALOG 消息。应用程序加载所有者绘制组合框使用的位图，然后调用应用程序定义的 InitGroupList 函数来初始化组合框。还选择组合框中的第一个列表项，然后调用应用程序定义的 InitFoodList 函数来初始化列表框。

在此示例中，所有者绘制的组合框是一个下拉列表框，其中包含四个食品组中每个组的名称。 InitGroupList 添加每个食品组的名称，并使用 CB_SETITEMDATA 消息将位图句柄与标识食品组的每个列表项相关联。

示例中的列表框包含所选食品组中食品的名称。 InitFoodList 重置列表框的内容，然后在当前食品组下拉列表框中添加当前食品选择的名称。

case WM_INITDIALOG:

    // Call an application-defined function to load bitmap resources.
    if (!LoadIconBitmaps())
    {
        EndDialog(hDlg, -1);
        break;
    }

    // Initialize the food groups combo box and select the first item.
    InitGroupList(hDlg);
    SendDlgItemMessage(hDlg, IDCOMBO, CB_SETCURSEL, 0, 0); 

    // Initialize the food list box and select the first item.
    InitFoodList(hDlg);
    SendDlgItemMessage(hDlg, IDLIST, LB_SETCURSEL, 0, 0); 

     return (INT_PTR)TRUE;

收到 WM_DESTROY 消息时，应用程序会删除所有者绘制组合框中的位图。

case WM_DESTROY:

    // Call the application-defined function to free the bitmap resources.
    DeleteIconBitmaps();
    break;

步骤 3：处理 WM_MEASUREITEM 消息。

所有者绘制的组合框将 WM_MEASUREITEM 消息发送到其父窗口或对话框过程，以便应用程序可以设置每个列表项的维度。由于示例组合框具有 CBS_OWNERDRAWFIXED 样式，因此系统只发送 WM_MEASUREITEM 消息一次。带有 CBS_OWNERDRAWVARIABLE 样式的组合框为每个列表项发送 WM_MEASUREITEM 消息。

lParam 参数是指向标识控件和列表项的 MEASUREITEMSTRUCT 结构的指针。它还包含列表项的默认维度。该示例修改 itemHeight 结构成员，以确保列表项足够高，足以容纳食品组位图。

case WM_MEASUREITEM:
    {
    // Set the height of the items in the food groups combo box.
    LPMEASUREITEMSTRUCT lpmis = (LPMEASUREITEMSTRUCT) lParam;

    if (lpmis->itemHeight < CY_BITMAP + 2)
        lpmis->itemHeight = CY_BITMAP + 2;

    break;
    }

步骤 4：处理 WM_DRAWITEM 消息。

每次应用程序必须重新绘制列表项时，所有者绘制组合框都会将 WM_DRAWITEM 消息发送到其父窗口或对话框过程。 lParam 参数是指向标识控件和列表项的 DRAWITEMSTRUCT 结构的指针。还包含绘制项所需的信息。

示例应用程序显示与食品组关联的列表项文本和位图。如果该项具有焦点，则还会绘制焦点矩形。在显示文本之前，该示例根据所选项设置前景色和背景色。由于组合框具有 CBS_HASSTRINGS 样式，因此组合框维护可以使用 CB_GETLBTEXT 消息检索的每个列表项的文本。

列表项使用的位图取决于食品组。 InitGroupList 使用 CB_SETITEMDATA 消息将位图句柄与每个列表项相关联。窗口过程从 DRAWITEMSTRUCT 结构的 itemData 成员中检索位图句柄。系统为每个食品组符号使用两个位图：一个使用 SRCAND 光栅操作擦除图像后面的不规则区域的单色位图和一个使用 SRCPAINT 光栅操作绘制图像的彩色位图。

case WM_DRAWITEM:
    {
    COLORREF clrBackground;
    COLORREF clrForeground;
    TEXTMETRIC tm;
    int x;
    int y;
    HRESULT hr;
    size_t cch;

    LPDRAWITEMSTRUCT lpdis = (LPDRAWITEMSTRUCT) lParam;
       
    if (lpdis->itemID == -1) // Empty item)
        break;

    // Get the food icon from the item data.
    hbmIcon = (HBITMAP) lpdis->itemData;

    // The colors depend on whether the item is selected.
    clrForeground = SetTextColor(lpdis->hDC, 
        GetSysColor(lpdis->itemState & ODS_SELECTED ?
        COLOR_HIGHLIGHTTEXT : COLOR_WINDOWTEXT));

    clrBackground = SetBkColor(lpdis->hDC, 
        GetSysColor(lpdis->itemState & ODS_SELECTED ?
        COLOR_HIGHLIGHT : COLOR_WINDOW));

    // Calculate the vertical and horizontal position.
    GetTextMetrics(lpdis->hDC, &tm);
    y = (lpdis->rcItem.bottom + lpdis->rcItem.top - tm.tmHeight) / 2;
    x = LOWORD(GetDialogBaseUnits()) / 4;

    // Get and display the text for the list item.
    SendMessage(lpdis->hwndItem, CB_GETLBTEXT,
        lpdis->itemID, (LPARAM) achTemp);

    hr = StringCchLength(achTemp, 256, &cch);
    if (FAILED(hr))
    {
        // TODO: Write error handler.
    }

    ExtTextOut(lpdis->hDC, CX_BITMAP + 2 * x, y,
        ETO_CLIPPED | ETO_OPAQUE, &lpdis->rcItem,
        achTemp, (UINT)cch, NULL);

    // Restore the previous colors.
    SetTextColor(lpdis->hDC, clrForeground);
    SetBkColor(lpdis->hDC, clrBackground);
    
    //  Draw the food icon for the item. 
    HDC hdc = CreateCompatibleDC(lpdis->hDC); 
    if (hdc == NULL) 
        break; 
 
    SelectObject(hdc, hbmMask); 
    BitBlt(lpdis->hDC, x, lpdis->rcItem.top + 1, 
        CX_BITMAP, CY_BITMAP, hdc, 0, 0, SRCAND); 
 
    SelectObject(hdc, hbmIcon); 
    BitBlt(lpdis->hDC, x, lpdis->rcItem.top + 1, 
        CX_BITMAP, CY_BITMAP, hdc, 0, 0, SRCPAINT); 
 
    DeleteDC(hdc); 
  
    // If the item has the focus, draw the focus rectangle.
    if (lpdis->itemState & ODS_FOCUS)
        DrawFocusRect(lpdis->hDC, &lpdis->rcItem);

    break;
    }

步骤 5：处理 WM_COMMAND 消息。

当对话框控件中发生事件时，该控件会通过 WM_COMMAND 消息通知对话框过程。该示例处理组合框、列表框和“确定”按钮中的通知消息。控件标识符位于 wParam 的低位字中，通知代码位于 wParam 的高位字中。

如果控件标识符为 IDCOMBO，则组合框中发生了一个事件。作为响应，对话框过程将忽略除 CBN_SELENDOK 以外的所有其他组合框事件，这表示已进行选择、关闭下拉列表框，并且应接受所做的更改。对话框过程调用 InitFoodList 以重置列表框的内容，并在下拉列表框中添加当前所选内容的名称。

如果控件标识符为 IDLIST，则列表框中发生了一个事件。这会导致对话框过程忽略除 LBN_DBLCLK（表示用户已双击列表项）之外的所有列表框事件。此事件的处理方式与选择“确定”按钮的方式相同。

如果控件标识符为 IDOK，则用户已选择“确定”按钮。作为响应，对话框过程将所选食品的名称插入应用程序的多行编辑控件中，然后调用 EndDialog 函数关闭对话框。

如果控件标识符为 IDCANCEL，则用户已单击“取消”按钮。作为响应，对话框过程调用 EndDialog 以关闭对话框。

case WM_COMMAND:
        switch (LOWORD(wParam)) 
        { 
            case IDCOMBO: 
                if (HIWORD(wParam) == CBN_SELENDOK) 
                { 
                    InitFoodList(hDlg); 
                    SendDlgItemMessage(hDlg, IDLIST, 
                        LB_SETCURSEL, 0, 0); 
                } 
                break; 
 
            case IDLIST: 
                if (HIWORD(wParam) != LBN_DBLCLK) 
                    break; 
 
            // For a double-click, process the OK case. 
            case IDOK: 
 
                // Get the text for the selected list item. 
                hwnd = GetDlgItem(hDlg, IDLIST); 

                // Here it is assumed the text can fit into achTemp.
                // If there is doubt, call LB_GETTEXTLENGTH first.
                SendMessage(hwnd, LB_GETTEXT, 
                    SendMessage(hwnd, LB_GETCURSEL, 0, 0), 
                    (LPARAM) achTemp); 
 
                // TODO: Do something with the selected text.
 
                EndDialog(hDlg, 0); 
                break; 
 
            case IDCANCEL: 
                hwnd = GetDlgItem(hDlg, IDCOMBO); 
                if (SendMessage(hwnd, CB_GETDROPPEDSTATE, 0, 0)) 
                    SendMessage(hwnd, CB_SHOWDROPDOWN, FALSE, 0); 
                else EndDialog(hDlg, 0); 
        } 
        break;

完整示例

以下是 Square Meal 对话框的对话框过程和支持函数。

#define ID_BREAD 0
#define ID_DAIRY 1
#define ID_FRUIT 2
#define ID_MEAT  3

#define CX_BITMAP 24
#define CY_BITMAP 24

HBITMAP hbmBread;
HBITMAP hbmDairy;
HBITMAP hbmMeat;
HBITMAP hbmFruit;
HBITMAP hbmMask;

HBITMAP hbmIcon;

// Message handler for Square Meal dialog box.
INT_PTR CALLBACK FoodDlgProc(HWND hDlg, UINT message, WPARAM wParam, 
    LPARAM lParam)
{
    UNREFERENCED_PARAMETER(lParam);
    TCHAR achTemp[256];
    HWND hwnd;

    switch (message)
    {
    case WM_INITDIALOG:

        // Call an application-defined function to load bitmap resources.
        if (!LoadIconBitmaps())
        {
            EndDialog(hDlg, -1);
            break;
        }

        // Initialize the food groups combo box and select the first item.
        InitGroupList(hDlg);
        SendDlgItemMessage(hDlg, IDCOMBO, CB_SETCURSEL, 0, 0); 

        // Initialize the food list box and select the first item.
        InitFoodList(hDlg);
        SendDlgItemMessage(hDlg, IDLIST, LB_SETCURSEL, 0, 0); 

         return (INT_PTR)TRUE;
   
    case WM_MEASUREITEM:
        {
        // Set the height of the items in the food groups combo box.
        LPMEASUREITEMSTRUCT lpmis = (LPMEASUREITEMSTRUCT) lParam;

        if (lpmis->itemHeight < CY_BITMAP + 2)
            lpmis->itemHeight = CY_BITMAP + 2;

        break;
        }

    case WM_DRAWITEM:
        {
        COLORREF clrBackground;
        COLORREF clrForeground;
        TEXTMETRIC tm;
        int x;
        int y;
        HRESULT hr;
        size_t cch;

        LPDRAWITEMSTRUCT lpdis = (LPDRAWITEMSTRUCT) lParam;
           
        if (lpdis->itemID == -1) // Empty item)
            break;

        // Get the food icon from the item data.
        hbmIcon = (HBITMAP) lpdis->itemData;

        // The colors depend on whether the item is selected.
        clrForeground = SetTextColor(lpdis->hDC, 
            GetSysColor(lpdis->itemState & ODS_SELECTED ?
            COLOR_HIGHLIGHTTEXT : COLOR_WINDOWTEXT));

        clrBackground = SetBkColor(lpdis->hDC, 
            GetSysColor(lpdis->itemState & ODS_SELECTED ?
            COLOR_HIGHLIGHT : COLOR_WINDOW));

        // Calculate the vertical and horizontal position.
        GetTextMetrics(lpdis->hDC, &tm);
        y = (lpdis->rcItem.bottom + lpdis->rcItem.top - tm.tmHeight) / 2;
        x = LOWORD(GetDialogBaseUnits()) / 4;

        // Get and display the text for the list item.
        SendMessage(lpdis->hwndItem, CB_GETLBTEXT,
            lpdis->itemID, (LPARAM) achTemp);

        hr = StringCchLength(achTemp, 256, &cch);
        if (FAILED(hr))
        {
            // TODO: Write error handler.
        }

        ExtTextOut(lpdis->hDC, CX_BITMAP + 2 * x, y,
            ETO_CLIPPED | ETO_OPAQUE, &lpdis->rcItem,
            achTemp, (UINT)cch, NULL);

        // Restore the previous colors.
        SetTextColor(lpdis->hDC, clrForeground);
        SetBkColor(lpdis->hDC, clrBackground);
        
        //  Draw the food icon for the item. 
        HDC hdc = CreateCompatibleDC(lpdis->hDC); 
        if (hdc == NULL) 
            break; 
 
        SelectObject(hdc, hbmMask); 
        BitBlt(lpdis->hDC, x, lpdis->rcItem.top + 1, 
            CX_BITMAP, CY_BITMAP, hdc, 0, 0, SRCAND); 
 
        SelectObject(hdc, hbmIcon); 
        BitBlt(lpdis->hDC, x, lpdis->rcItem.top + 1, 
            CX_BITMAP, CY_BITMAP, hdc, 0, 0, SRCPAINT); 
 
        DeleteDC(hdc); 
      
        // If the item has the focus, draw the focus rectangle.
        if (lpdis->itemState & ODS_FOCUS)
            DrawFocusRect(lpdis->hDC, &lpdis->rcItem);

        break;
        }

    case WM_COMMAND:
            switch (LOWORD(wParam)) 
            { 
                case IDCOMBO: 
                    if (HIWORD(wParam) == CBN_SELENDOK) 
                    { 
                        InitFoodList(hDlg); 
                        SendDlgItemMessage(hDlg, IDLIST, 
                            LB_SETCURSEL, 0, 0); 
                    } 
                    break; 
 
                case IDLIST: 
                    if (HIWORD(wParam) != LBN_DBLCLK) 
                        break; 
 
                // For a double-click, process the OK case. 
                case IDOK: 
 
                    // Get the text for the selected list item. 
                    hwnd = GetDlgItem(hDlg, IDLIST); 

                    // Here it is assumed the text can fit into achTemp.
                    // If there is doubt, call LB_GETTEXTLENGTH first.
                    SendMessage(hwnd, LB_GETTEXT, 
                        SendMessage(hwnd, LB_GETCURSEL, 0, 0), 
                        (LPARAM) achTemp); 
 
                    // TODO: Do something with the selected text.
 
                    EndDialog(hDlg, 0); 
                    break; 
 
                case IDCANCEL: 
                    hwnd = GetDlgItem(hDlg, IDCOMBO); 
                    if (SendMessage(hwnd, CB_GETDROPPEDSTATE, 0, 0)) 
                        SendMessage(hwnd, CB_SHOWDROPDOWN, FALSE, 0); 
                    else EndDialog(hDlg, 0); 
            } 
            break; 

    case WM_DESTROY:

        // Call the application-defined function to free the bitmap resources.
        DeleteIconBitmaps();
        break;
    }
    return (INT_PTR)FALSE;
}

// Loads string resources and adds them as items to the drop-down list of
//   the food groups combo box. The bitmap handle of each item&#39;s icon is
//   stored as item data for easy access when the item needs to be drawn.
// 
void InitGroupList(HWND hDlg)
{
    TCHAR achTemp[256];
    DWORD dwIndex;

    // Get the handle of the food groups combo box.
    HWND hwndGroupsBox = GetDlgItem(hDlg, IDCOMBO);

    LoadString(hInst, IDS_BREAD, achTemp, sizeof(achTemp)/sizeof(TCHAR));
    dwIndex = SendMessage(hwndGroupsBox, CB_ADDSTRING, 0, (LPARAM) achTemp);
    SendMessage(hwndGroupsBox, CB_SETITEMDATA, dwIndex, (LPARAM) hbmBread);
    
    LoadString(hInst, IDS_DAIRY, achTemp, sizeof(achTemp)/sizeof(TCHAR)); 
    dwIndex = SendMessage(hwndGroupsBox, CB_ADDSTRING, 0, (LPARAM) achTemp);
    SendMessage(hwndGroupsBox, CB_SETITEMDATA, dwIndex, (LPARAM) hbmDairy);

    LoadString(hInst, IDS_FRUIT, achTemp, sizeof(achTemp)/sizeof(TCHAR));
    dwIndex = SendMessage(hwndGroupsBox, CB_ADDSTRING, 0, (LPARAM) achTemp);
    SendMessage(hwndGroupsBox, CB_SETITEMDATA, dwIndex, (LPARAM) hbmFruit); 

    LoadString(hInst, IDS_MEAT, achTemp, sizeof(achTemp)/sizeof(TCHAR)); 
    dwIndex = SendMessage(hwndGroupsBox, CB_ADDSTRING, 0, (LPARAM) achTemp);
    SendMessage(hwndGroupsBox, CB_SETITEMDATA, dwIndex, (LPARAM) hbmMeat);

    return;
}

// Fills the food list based on the selected item in the food groups
//   combo box.
void InitFoodList(HWND hDlg)
{
    TCHAR achTemp[256];

    HWND hwndGroupsBox = GetDlgItem(hDlg, IDCOMBO);
    HWND hwndFoodList = GetDlgItem(hDlg, IDLIST);

    // Clear the list contents.
    SendMessage(hwndFoodList, LB_RESETCONTENT, 0, 0);

    // Find out which food group is selected.
    int idFoodGroup = SendMessage(hwndGroupsBox, CB_GETCURSEL, 0, 0);

    switch (idFoodGroup)
    {
    case ID_BREAD:
        LoadString(hInst, IDS_OAT, achTemp, sizeof(achTemp)/sizeof(TCHAR));
        SendMessage(hwndFoodList, LB_ADDSTRING, 0, (LPARAM) achTemp);

        LoadString(hInst, IDS_WHEAT, achTemp, sizeof(achTemp)/sizeof(TCHAR));
        SendMessage(hwndFoodList, LB_ADDSTRING, 0, (LPARAM) achTemp);

        LoadString(hInst, IDS_RYE, achTemp, sizeof(achTemp)/sizeof(TCHAR));
        SendMessage(hwndFoodList, LB_ADDSTRING, 0, (LPARAM) achTemp);
        break;

    case ID_DAIRY:
        LoadString(hInst, IDS_CHEDDAR, achTemp, sizeof(achTemp)/sizeof(TCHAR));
        SendMessage(hwndFoodList, LB_ADDSTRING, 0, (LPARAM) achTemp);

        LoadString(hInst, IDS_MILK, achTemp, sizeof(achTemp)/sizeof(TCHAR));
        SendMessage(hwndFoodList, LB_ADDSTRING, 0, (LPARAM) achTemp);

        LoadString(hInst, IDS_PROCESSED, achTemp, sizeof(achTemp)/sizeof(TCHAR));
        SendMessage(hwndFoodList, LB_ADDSTRING, 0, (LPARAM) achTemp);

        LoadString(hInst, IDS_SWISS, achTemp, sizeof(achTemp)/sizeof(TCHAR));
        SendMessage(hwndFoodList, LB_ADDSTRING, 0, (LPARAM) achTemp);
        
        break;

    case ID_FRUIT:
        LoadString(hInst, IDS_APPLES, achTemp, sizeof(achTemp)/sizeof(TCHAR));
        SendMessage(hwndFoodList, LB_ADDSTRING, 0, (LPARAM) achTemp);

        LoadString(hInst, IDS_BANANAS, achTemp, sizeof(achTemp)/sizeof(TCHAR));
        SendMessage(hwndFoodList, LB_ADDSTRING, 0, (LPARAM) achTemp);

        LoadString(hInst, IDS_ORANGES, achTemp, sizeof(achTemp)/sizeof(TCHAR));
        SendMessage(hwndFoodList, LB_ADDSTRING, 0, (LPARAM) achTemp);

        break;

    case ID_MEAT:
        LoadString(hInst, IDS_BEEF, achTemp, sizeof(achTemp)/sizeof(TCHAR));
        SendMessage(hwndFoodList, LB_ADDSTRING, 0, (LPARAM) achTemp);

        LoadString(hInst, IDS_CHICKEN, achTemp, sizeof(achTemp)/sizeof(TCHAR));
        SendMessage(hwndFoodList, LB_ADDSTRING, 0, (LPARAM) achTemp);

        LoadString(hInst, IDS_PORK, achTemp, sizeof(achTemp)/sizeof(TCHAR));
        SendMessage(hwndFoodList, LB_ADDSTRING, 0, (LPARAM) achTemp);

        break;

    default:
        break;
    }

    return;
}

// Loads the food icon bitmaps from the application resources.
//
BOOL LoadIconBitmaps(void)
{
    hbmBread = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_BREAD));

    if (hbmBread != NULL)
         hbmDairy = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_DAIRY));

    if (hbmDairy != NULL)
         hbmMeat = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_MEAT));

    if (hbmMeat != NULL)
        hbmFruit = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_FRUIT));
    
    if (hbmFruit != NULL)
        hbmMask = LoadBitmap(hInst, MAKEINTRESOURCE(IDB_MASK));

    if (hbmMask != NULL)
        return TRUE;
        
    return FALSE;
}

// Frees the icon bitmps.
//
void DeleteIconBitmaps(void)
{
    FreeResource(reinterpret_cast<HGLOBAL>(hbmBread));
    FreeResource(reinterpret_cast<HGLOBAL>(hbmDairy));
    FreeResource(reinterpret_cast<HGLOBAL>(hbmMeat));
    FreeResource(reinterpret_cast<HGLOBAL>(hbmFruit));
    FreeResource(reinterpret_cast<HGLOBAL>(hbmMask));
}

使用组合框

通过

如何创建所有者绘制的组合框

需要了解的事项

技术

先决条件

说明

步骤 1：创建“所有者绘制”对话框

步骤 2：处理对话框中的 WM_INITDIALOG 和 WM_DESTROY 消息。

步骤 3：处理 WM_MEASUREITEM 消息。

步骤 4：处理 WM_DRAWITEM 消息。

步骤 5：处理 WM_COMMAND 消息。

完整示例

反馈

其他资源

通过

如何创建所有者绘制的组合框

需要了解的事项

技术

先决条件

说明

步骤 1：创建“所有者绘制”对话框

步骤 2：处理对话框中的 WM_INITDIALOG 和 WM_DESTROY 消息。

步骤 3：处理 WM_MEASUREITEM 消息。

步骤 4：处理 WM_DRAWITEM 消息。

步骤 5：处理 WM_COMMAND 消息。

完整示例

相关主题

反馈

其他资源