C++Builder 定制系統選單：添加「前端顯示」切換功能

實現思路

系統選單無可視化組件，需通過 API 動態修改：GetSystemMenu 獲取句柄，AppendMenu 添加項目，WM_SYSCOMMAND 消息處理點擊事件。

完整實現步驟

1. FormCreate 初始化系統選單

void __fastcall TForm1::FormCreate(TObject *Sender) {
    AppendMenu(GetSystemMenu(Handle, FALSE), MF_SEPARATOR, 0, "");
    AppendMenu(GetSystemMenu(Handle, FALSE), MF_STRING, 200, "前端顯示(&A)");
}

2. 聲明消息處理映射 (Unit1.h)

#include 
// ...
public:
    MESSAGE void __fastcall SystemMenuCommand(TWMMenuSelect &Msg);
BEGIN_MESSAGE_MAP
    MESSAGE_HANDLER(WM_SYSCOMMAND, TWMMenuSelect, SystemMenuCommand)
END_MESSAGE_MAP(TForm)

3. 處理邏輯：切換 FormStyle 並更新選單狀態

void __fastcall TForm1::SystemMenuCommand(TWMMenuSelect &Msg) {
    TForm::Dispatch(&Msg);
    if (Msg.IDItem == 200) {
        if (FormStyle == fsNormal) {
            FormStyle = fsStayOnTop;
            // 重建選單並標記勾選
            AppendMenu(GetSystemMenu(Handle, FALSE), MF_SEPARATOR, 0, "");
            AppendMenu(GetSystemMenu(Handle, FALSE), MF_STRING, 200, "前端顯示(&A)");
            ModifyMenu(GetSystemMenu(Handle, FALSE), 200, MF_CHECKED, 200, "前端顯示(&A)");
        } else {
            FormStyle = fsNormal;
            AppendMenu(GetSystemMenu(Handle, FALSE), MF_SEPARATOR, 0, "");
            AppendMenu(GetSystemMenu(Handle, FALSE), MF_STRING, 200, "前端顯示(&A)");
        }
    }
}

關鍵點

• 每次切換需重建選單項，因 GetSystemMenu(Handle, FALSE) 返回副本。
• MF_CHECKED 提供視覺反饋。
• 命令 ID (200) 需在 WM_SYSCOMMAND 中精確匹配。