如何为组合框创建子类

  • 项目

本主题演示如何子类化组合框。 C++ 示例应用程序创建了一个工具栏窗口，其中包含两个组合框。 通过对组合框内的编辑控件进行子类化，工具栏窗口可拦截 TAB、ENTER 和 ESC 键，否则它们就会被忽略。

需要了解的事项

技术

先决条件

  • C/C++
  • Windows 用户界面编程

说明

处理 WM_CREATE 消息

应用程序会处理 WM_CREATE 消息，以便创建两个组合框控件作为子窗口。

//  Create two combo box child windows. 
dwBaseUnits = GetDialogBaseUnits(); 
 
hwndCombo1 = CreateWindow(L"COMBOBOX", L"", 
    CBS_DROPDOWN | WS_CHILD | WS_VISIBLE, 
    (6 * LOWORD(dwBaseUnits)) / 4, 
    (2 * HIWORD(dwBaseUnits)) / 8, 
    (100 * LOWORD(dwBaseUnits)) / 4, 
    (50 * HIWORD(dwBaseUnits)) / 8, 
    hwnd, NULL, NULL, NULL);  
 
hwndCombo2 = CreateWindow(L"COMBOBOX", L"", 
    CBS_DROPDOWN | WS_CHILD | WS_VISIBLE, 
    (112 * LOWORD(dwBaseUnits)) / 4, 
    (2 * HIWORD(dwBaseUnits)) / 8, 
    (100 * LOWORD(dwBaseUnits)) / 4, 
    (50 * HIWORD(dwBaseUnits)) / 8, 
    hwnd, NULL, hInst, NULL);

然后，应用程序会对每个组合框中的编辑控件（选择字段）进行子类化，因为它们会接收简单组合框以及下拉组合框的字符输入。 最后，它会调用 ChildWindowFromPoint 函数来检索每个编辑控件的句柄。

为了对编辑控件进行子类化，应用程序会调用 SetWindowLong 函数，将指向类窗口过程的指针替换为指向应用程序定义的 SubClassProc 函数的指针。 指向原始窗口过程的指针保存在全局变量 lpfnEditWndProc 中。

SubClassProc 会拦截 TAB、ENTER 和 ESC 键，并通过发送应用程序定义的消息（WM_TAB、WM_ESC 和 WM_ENTER）来通知工具栏窗口。 SubClassProc 使用 CallWindowProc 函数将大部分信息传递给原始窗口过程 lpfnEditWndProc。

//  Get the edit window handle to each combo box. 
pt.x = 1; 
pt.y = 1; 
hwndEdit1 = ChildWindowFromPoint(hwndCombo1, pt); 
hwndEdit2 = ChildWindowFromPoint(hwndCombo2, pt); 
 
//  Change the window procedure for both edit windows 
//  to the subclass procedure. 
lpfnEditWndProc = (WNDPROC) SetWindowLongPtr(hwndEdit1, 
    GWLP_WNDPROC, (LONG_PTR) SubClassProc); 
 
SetWindowLongPtr(hwndEdit2, GWLP_WNDPROC, (LONG_PTR) SubClassProc);

处理 WM_SETFOCUS 消息

当工具栏窗口接收到输入焦点时，它会立即将焦点设置到工具栏中的第一个组合框。 为此，示例会调用 SetFocus 函数来响应 WM_SETFOCUS 消息。

case WM_SETFOCUS: 
    SetFocus(hwndCombo1); 
    break;

处理应用程序定义的消息

当用户在组合框中按下 TAB、ENTER 或 ESC 键时，SubClassProc 函数就会向工具栏窗口发送应用程序定义的消息。 按 TAB 键时会发送 WM_TAB 消息，按 ESC 键时会发送WM_ESC 消息，而按 ENTER 键时会发送 WM_ENTER 消息。

该示例通过将焦点设置为工具栏中的下一个组合框来处理 WM_TAB 消息。 它通过将焦点设置为主应用程序窗口来处理 WM_ESC 消息。

  case WM_TAB: 
      if (GetFocus() == hwndEdit1) 
          SetFocus(hwndCombo2); 
      else 
          SetFocus(hwndCombo1); 
      break; 
 
  case WM_ESC: 
       hwndCombo = GetFocus() == hwndEdit1 ? hwndCombo1 : hwndCombo2; 
 
       // Clear the current selection. 
       SendMessage(hwndCombo, CB_SETCURSEL, 
          (WPARAM) (-1), 0); 
 
      //  Set the focus to the main window. 
      SetFocus(hwndMain); 
      break;

在响应 WM_ENTER 消息时，该示例会确保组合框的当前选择有效，然后将焦点设置为主应用程序窗口。 如果组合框未包含当前选择，则示例将使用 CB_FINDSTRINGEXACT 消息来搜索与选择字段内容相匹配的列表项目。 如果匹配，则示例会设置当前的选择；否则，它会添加一个新的列表项目。

case WM_ENTER: 
    hwndCombo = GetFocus() == hwndEdit1 ? hwndCombo1 : hwndCombo2; 
    SetFocus(hwndMain); 
 
    //  If there is no current selection, set one. 
    if (SendMessage(hwndCombo, CB_GETCURSEL, 0, 0) 
            == CB_ERR) 
    { 
        if (SendMessage(hwndCombo, WM_GETTEXT, 
                sizeof(achTemp), (LPARAM) achTemp) == 0) 
            break;      //  Empty selection field 
        dwIndex = SendMessage(hwndCombo, 
            CB_FINDSTRINGEXACT, (WPARAM) (-1), 
            (LPARAM) achTemp); 
 
        //  Add the string, if necessary, and select it. 
        if (dwIndex == CB_ERR) 
            dwIndex = SendMessage(hwndCombo, CB_ADDSTRING, 
                0, (LPARAM) achTemp); 
        if (dwIndex != CB_ERR) 
            SendMessage(hwndCombo, CB_SETCURSEL, 
                dwIndex, 0); 
    } 
    break; 
       
    // . 
    // .  Process additional messages. 
    // . 
 
default: 
    return DefWindowProc(hwnd, msg, wParam, lParam);

完整示例

以下是工具栏的窗口过程和两个组合框的子类过程。

#define WM_TAB (WM_USER) 
#define WM_ESC (WM_USER + 1) 
#define WM_ENTER (WM_USER + 2) 

//  Global variables
HWND    hwndMain; 
WNDPROC lpfnEditWndProc; //  Original wndproc for the combo box 

//  Prototypes
LRESULT CALLBACK SubClassProc( HWND, UINT, WPARAM, LPARAM );
 
/******************************************************** 
 
    FUNCTION:   ToolbarWindowProc 
 
    PURPOSE:    Window procedure for the toolbar window 
 
*********************************************************/ 
 
LRESULT CALLBACK ToolbarWindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) 
{ 
    static HWND   hwndEdit1; 
    static HWND   hwndEdit2; 
    static HWND   hwndCombo1; 
    static HWND   hwndCombo2; 
    POINT       pt; 
    DWORD       dwBaseUnits; 
    HWND        hwndCombo; 
    DWORD       dwIndex; 
    char achTemp[256];       //  Temporary buffer 
 
    switch (msg) 
    { 
        case WM_CREATE: 
            //  Create two combo box child windows. 
            dwBaseUnits = GetDialogBaseUnits(); 
 
            hwndCombo1 = CreateWindow(L"COMBOBOX", L"", 
                CBS_DROPDOWN | WS_CHILD | WS_VISIBLE, 
                (6 * LOWORD(dwBaseUnits)) / 4, 
                (2 * HIWORD(dwBaseUnits)) / 8, 
                (100 * LOWORD(dwBaseUnits)) / 4, 
                (50 * HIWORD(dwBaseUnits)) / 8, 
                hwnd, NULL, NULL, NULL);  
 
            hwndCombo2 = CreateWindow(L"COMBOBOX", L"", 
                CBS_DROPDOWN | WS_CHILD | WS_VISIBLE, 
                (112 * LOWORD(dwBaseUnits)) / 4, 
                (2 * HIWORD(dwBaseUnits)) / 8, 
                (100 * LOWORD(dwBaseUnits)) / 4, 
                (50 * HIWORD(dwBaseUnits)) / 8, 
                hwnd, NULL, hInst, NULL); 
            
            //  Get the edit window handle to each combo box. 
            pt.x = 1; 
            pt.y = 1; 
            hwndEdit1 = ChildWindowFromPoint(hwndCombo1, pt); 
            hwndEdit2 = ChildWindowFromPoint(hwndCombo2, pt); 
 
            //  Change the window procedure for both edit windows 
            //  to the subclass procedure. 
            lpfnEditWndProc = (WNDPROC) SetWindowLongPtr(hwndEdit1, 
                GWLP_WNDPROC, (LONG_PTR) SubClassProc); 
 
            SetWindowLongPtr(hwndEdit2, GWLP_WNDPROC, (LONG_PTR) SubClassProc); 

            break; 

        case WM_SETFOCUS: 
            SetFocus(hwndCombo1); 
            break; 

        case WM_TAB: 
            if (GetFocus() == hwndEdit1) 
                SetFocus(hwndCombo2); 
            else 
                SetFocus(hwndCombo1); 
            break; 
 
        case WM_ESC: 
             hwndCombo = GetFocus() == hwndEdit1 ? hwndCombo1 : hwndCombo2; 
 
             // Clear the current selection. 
             SendMessage(hwndCombo, CB_SETCURSEL, 
                (WPARAM) (-1), 0); 
 
            //  Set the focus to the main window. 
            SetFocus(hwndMain); 
            break;

        case WM_ENTER: 
            hwndCombo = GetFocus() == hwndEdit1 ? hwndCombo1 : hwndCombo2; 
            SetFocus(hwndMain); 
 
            //  If there is no current selection, set one. 
            if (SendMessage(hwndCombo, CB_GETCURSEL, 0, 0) 
                    == CB_ERR) 
            { 
                if (SendMessage(hwndCombo, WM_GETTEXT, 
                        sizeof(achTemp), (LPARAM) achTemp) == 0) 
                    break;      //  Empty selection field 
                dwIndex = SendMessage(hwndCombo, 
                    CB_FINDSTRINGEXACT, (WPARAM) (-1), 
                    (LPARAM) achTemp); 
 
                //  Add the string, if necessary, and select it. 
                if (dwIndex == CB_ERR) 
                    dwIndex = SendMessage(hwndCombo, CB_ADDSTRING, 
                        0, (LPARAM) achTemp); 
                if (dwIndex != CB_ERR) 
                    SendMessage(hwndCombo, CB_SETCURSEL, 
                        dwIndex, 0); 
            } 
            break; 
       
            // . 
            // .  Process additional messages. 
            // . 
 
        default: 
            return DefWindowProc(hwnd, msg, wParam, lParam); 
    } 
    return 0; 
} 
 
 
/******************************************************** 
 
    FUNCTION:   SubClassProc 
 
    PURPOSE:    Process TAB and ESCAPE keys, and pass all 
                other messages to the class window 
                procedure. 
 
*********************************************************/ 
LRESULT CALLBACK SubClassProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) 
{ 
    switch (msg) 
    { 
        case WM_KEYDOWN: 
            switch (wParam) 
            { 
                case VK_TAB: 
                    SendMessage(hwndMain, WM_TAB, 0, 0); 
                    return 0; 
                case VK_ESCAPE: 
                    SendMessage(hwndMain, WM_ESC, 0, 0); 
                    return 0; 
                case VK_RETURN: 
                    SendMessage(hwndMain, WM_ENTER, 0, 0); 
                    return 0; 
            } 
            break; 
 
        case WM_KEYUP: 
        case WM_CHAR: 
            switch (wParam) 
            { 
                case VK_TAB: 
                case VK_ESCAPE: 
                case VK_RETURN: 
                    return 0; 
            } 
    } 
 
    //  Call the original window procedure for default processing. 
     return CallWindowProc(lpfnEditWndProc, hwnd, msg, wParam, lParam); 
}

关于组合框

ComboBox 控件参考

使用组合框

ComboBox