虚拟键码到 unicode 的映射受写入 std::cout 的影响？

Question

我遇到了一个奇怪的问题，我真的不知道如何解决。我正在用 C++ 编写代码，它应该在按下键时触发事件。我可以使用GetAsyncKeystate 很好地检测按键并释放，但我无法可靠地将检测到的按键状态转换为 unicode。 （请注意，我使用的是 Qt，但这并不重要）

我的新闻/发布检测：

// This function is called in a loop
void KeyboardApi::Check()
{
    bool stat = false;
    for (int i = 7; i < 255; i++) { // 0 undefined, 3 VK_CANCEL can be ignored, 1 2 4 5 6 mouse keys, these are ignored
        stat = ((GetAsyncKeyState(i) & 0x8000) != 0);

        if (this->first_time) { // To prevent reporting keypresses upon initialization
            this->first_time = false;
            this->keystate[i] = stat;
            continue;
        }

        if (stat != this->keystate[i]) {
            this->keystate[i] = stat;

            if (i == VK_SHIFT)
                this->shift = stat;
            else if (i == VK_CONTROL)
                this->ctrl = stat;
            else if (i == VK_MENU)
                this->alt = stat;

            HKL locale = GetKeyboardLayout(GetCurrentThreadId());

            // ---!! If this portion is commented, the code does not work correctly.
            //       if this portion is *not* commented, the code works fine...
            /*
            std::wcout << "args for keycode_to_unicode:" << std::endl
                       << "  keycode: " << i << std::endl
                       << "  locale: " << locale << std::endl
                       << "  shift: " << this->shift << std::endl;
            */
            // ---!!

            QString key_string = keycode_to_unicode(i, locale, this->shift);

            if (stat)
                std::wcout << "Key pressed:  " << i <<  " unicode: " << key_string.toStdWString() << std::endl;
        }
    }
}

还有 keycode_to_unicode 函数：

QString keycode_to_unicode(unsigned int key, HKL keyboardLayoutHandle, bool shiftPressed)
{
    int scanCodeEx = MapVirtualKeyExW(key, MAPVK_VK_TO_VSC_EX, keyboardLayoutHandle);

    if (scanCodeEx > 0) {
        unsigned char lpKeyState[256];

        if (shiftPressed) {
            lpKeyState[VK_SHIFT] = 0x80;
            lpKeyState[VK_LSHIFT] = 0x80;
        }

        wchar_t buffer[5];

        int rc = ToUnicodeEx(key, scanCodeEx, lpKeyState, buffer, 5, 0, keyboardLayoutHandle);

        if (rc > 0) {
            return QString::fromWCharArray(buffer);
        } else {
            // It's a dead key; let's flush out whats stored in the keyboard state.
            rc = ToUnicodeEx(key, scanCodeEx, lpKeyState, buffer, 5, 0, keyboardLayoutHandle);
            return QString();
        }
    }

    return QString();
}

所以奇怪的是，当我在那里有调试输出时，KeyboardApi::Check() 工作正常，但是当我没有它时，转换为 unicode 会出错。例如，当我第一次按下'A'键时，输出'a'。第二次，'β'，'β'等

编辑： 你可能会问自己为什么我不使用 Qt 的内置 onKeyPress... 这是因为我的代码被注入到其他进程中，所以我不能使用这种方法。

Answer 1

原来是keycode_to_unicode的问题！

在我的代码中，我有：

unsigned char lpKeyState[256];

表示数组未初始化；它的内容可以是任何东西。替换为：

unsigned char lpKeyState[256] = {0};

修复了奇数输入的问题。原来我还有一些其他问题（特别是死键）。我稍微修改了我的代码，现在能够在按下死键时正确检测到死键，尽管我还没有成功地将死键与后续字符组合以检测带重音的字符。为了完整起见，下面是修改后的代码：

注意：它确实不考虑大写锁定。

QString KeyboardApi::keycode_to_unicode(unsigned int key, HKL keyboardLayoutHandle, bool shiftPressed, bool ctrlPressed, bool altPressed, bool capslock)
{
    int scanCodeEx = MapVirtualKeyExW(key, MAPVK_VK_TO_VSC_EX, keyboardLayoutHandle);

    if (scanCodeEx <= 0)
        return QString();

    unsigned char lpKeyState[256] = {0};

    if (shiftPressed) {
        lpKeyState[VK_SHIFT] = 0x80;
        lpKeyState[VK_LSHIFT] = 0x80;
    }

    if (ctrlPressed)
        lpKeyState[VK_CONTROL] = 0x80;

    if (altPressed)
        lpKeyState[VK_MENU] = 0x80;

    if (capslock)
        lpKeyState[VK_CAPITAL] = 0x01;

    wchar_t buffer[5];

    ToUnicodeEx(key, scanCodeEx, lpKeyState, buffer, 5, 0, keyboardLayoutHandle);

    QString ret = QString::fromWCharArray(buffer);
    ret.truncate(1);

    return ret;
}

Qt::Key KeyboardApi::unicode_to_qtkey(QString key)
{
    unsigned int code = key[0].unicode();
    if (key[0].unicode() >= 'a' && key[0].unicode() <= 'z') {
        code = key[0].unicode() - 'a' + Qt::Key_A;
    }

    return (Qt::Key)code;
}

void KeyboardApi::Check()
{
    bool init = this->first_time;

    if (this->first_time)
        this->first_time = false;

    bool stat = false;
    for (int i = 7; i < 255; i++) { // yes, 255 is NOT valid! // 0 undefined, 3 VK_CANCEL can be ignored, 1 2 4 5 6 mouse keys
        stat = ((GetAsyncKeyState(i) & 0x8000) != 0);

        if (stat == this->keystate[i])
            continue;

        this->keystate[i] = stat;

        if (i == VK_SHIFT)
            this->shift = stat;
        else if (i == VK_CONTROL)
            this->ctrl = stat;
        else if (i == VK_MENU)
            this->alt = stat;
        else if (i == VK_CAPITAL)
            this->capslock = stat;

        HKL locale = GetKeyboardLayout(GetCurrentThreadId());

        QString key_string = keycode_to_unicode(i, locale, this->shift, this->ctrl, this->alt, false);

        // See qkeymapper_win.cpp for the table used to convert windows virtual key codes to Qt::Key
        Qt::Key key = key_string.isEmpty() ? (Qt::Key)win_vk_to_qt_key[i] : unicode_to_qtkey(key_string);

        if (init || i == VK_SHIFT || i == VK_CONTROL || i == VK_MENU)
            continue;

        if (stat) {
            emit this->OnKeyDown(this, QKeyEvent(QEvent::KeyPress, key, mods, key_string));
        } else
            emit this->OnKeyUp(this, QKeyEvent(QEvent::KeyPress, key, mods, key_string));
    }
}