Qt获取Capslock键（大小写键）状态

1.前言

最近需要qt获取按键ascii码，可是QKeyEvent::key()返回的是键码，不是ascii码（0-127），需要从键码转ascii码。遇到的问题是不知道如何获取Capslock键状态，网友说用LOBYTE(GetKeyState(VK_CAPITAL))，但如何跨平台呢，QT不该只用windows吧？

2.解决办法

用QKeyEvent::nativeModifiers()获取CapsLock键状态，

keyEvent->nativeModifiers() & CapsLock;

依据源码：

bool QKeyMapperPrivate::translateKeyEvent(QWidget *widget, const MSG &msg, bool grab) {     Q_Q(QKeyMapper);     Q_UNUSED(q); // Strange, but the compiler complains on q not being referenced, even if it is..     bool k0 = false;     bool k1 = false;     int  msgType = msg.message;     // WM_CHAR messages already contain the character in question so there is     // no need to fiddle with our key map. In any other case add this key to the     // keymap if it is not present yet.     if (msg.message != WM_CHAR)         updateKeyMap(msg);     const quint32 scancode = (msg.lParam >> 16) & scancodeBitmask;     const quint32 vk_key = msg.wParam;     quint32 nModifiers = 0; #if defined(Q_OS_WINCE)         nModifiers |= (GetKeyState(VK_SHIFT  ) < 0 ? ShiftAny : 0);         nModifiers |= (GetKeyState(VK_CONTROL) < 0 ? ControlAny : 0);         nModifiers |= (GetKeyState(VK_MENU   ) < 0 ? AltAny : 0);         nModifiers |= (GetKeyState(VK_LWIN   ) < 0 ? MetaLeft : 0);         nModifiers |= (GetKeyState(VK_RWIN   ) < 0 ? MetaRight : 0); #else         // Map native modifiers to some bit representation         nModifiers |= (GetKeyState(VK_LSHIFT  ) & 0x80 ? ShiftLeft : 0);         nModifiers |= (GetKeyState(VK_RSHIFT  ) & 0x80 ? ShiftRight : 0);         nModifiers |= (GetKeyState(VK_LCONTROL) & 0x80 ? ControlLeft : 0);         nModifiers |= (GetKeyState(VK_RCONTROL) & 0x80 ? ControlRight : 0);         nModifiers |= (GetKeyState(VK_LMENU   ) & 0x80 ? AltLeft : 0);         nModifiers |= (GetKeyState(VK_RMENU   ) & 0x80 ? AltRight : 0);         nModifiers |= (GetKeyState(VK_LWIN    ) & 0x80 ? MetaLeft : 0);         nModifiers |= (GetKeyState(VK_RWIN    ) & 0x80 ? MetaRight : 0);         // Add Lock keys to the same bits         nModifiers |= (GetKeyState(VK_CAPITAL ) & 0x01 ? CapsLock : 0);         nModifiers |= (GetKeyState(VK_NUMLOCK ) & 0x01 ? NumLock : 0);         nModifiers |= (GetKeyState(VK_SCROLL  ) & 0x01 ? ScrollLock : 0); #endif // Q_OS_WINCE     if (msg.lParam & ExtendedKey)         nModifiers |= msg.lParam & ExtendedKey;

3. 总结

QKeyEvent::key() 返回虚拟键码，比如Qt::Key_Space

QKeyEvent::modifiers() 返回shift、ctrl、alt、meta和groupswitch虚拟键状态

QKeyEvent::nativeScanCode() 返回实际键码

QKeyEvent::nativeModifiers() 返回CapsLock、NumLock和ScrollLock实际键状态

QKeyEvent::isAutoRepeat() 判断长按

网络资源只作参考，多跟踪源码，以源码为主

4.参考文献

【1】https://blog.youkuaiyun.com/stpeace/article/details/51619704

【2】https://bbs.youkuaiyun.com/topics/360138798

【3】https://blog.youkuaiyun.com/robertkun/article/details/38081301