class AbstractKeyboard : public QWidget
{
    Q_OBJECT
public:
    AbstractKeyboard(QWidget *parent = 0);
    ~AbstractKeyboard();

    const QString name();
    void setName(const QString &name);

public slots:
    virtual void update(const QString &text);
    void onKeyPressed(int key, QString value);

signals:
    void keyPressed(int key, QString value);
};

class Keyboard : public AbstractKeyboard
{
    Q_OBJECT
public:
    Keyboard(QWidget *parent = NULL);

protected:
    void resizeEvent(QResizeEvent *e);

private slots:
    void switchCapsLock();
    void switchSpecialChar();
    void switchEnOrCh();
};

class KeyButton : public QPushButton
{
    Q_OBJECT
public:
    enum Type { Auto = 0, LowerCase, UpperCase, SpecialChar };

    struct Mode {
        int key;          /* Qt::Key */
        QString value;    /* text */
        QString display;  /* display text */
        Type type;        /* default: Auto */
    };

    KeyButton(const QList<Mode> modes = QList<Mode>(), QWidget *parent = NULL);
    Mode mode();

    void onReponse(const QObject* receiverObj, const QString &receiver);

    void switchCapsLock();
    void switchSpecialChar();
    void switching(); /* Cycle switch. */

signals:
    void pressed(int key, QString value);
};

https://github.com/aeagean/QtKeyboard