Qt 键盘事件

QEvent::KeyPress

键盘按下时，触发该事件，它对应的子类是QKeyEvent

QEvent::KeyRelease

键盘抬起时，触发该事件，它对应的子类是QKeyEvent

1. 键盘按下、释放事件的基本使用

只需重写keyPressEvent()和keyPressEvent()两个函数即可

首先，在key_widget.h中添加两个函数的声明

// key_widget.h
protected:
    // 重写键盘事件
    void keyPressEvent(QKeyEvent *event);
    void keyReleaseEvent(QKeyEvent *event);
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然后，来到key_widget.cpp实现这2个函数：

// key_widget.cpp
void KeyWidget::keyPressEvent(QKeyEvent* event) {
    // 1. 单个按键
    switch (event->key()) {
        case Qt::Key_Return:
            qDebug() << "Enter";
            break;
        case Qt::Key_Escape:
            qDebug() << "Esc";
            break;
        case Qt::Key_Control:
            qDebug() << "Ctrl";
            break;
        case Qt::Key_Shift:
            qDebug() << "Shift";
            break;
        case Qt::Key_Alt:
            qDebug() << "Alt";
            break;
        case Qt::Key_W:
            qDebug() << "Up";
            lbl->move(lbl->x(), lbl->y() - 20);
            if (lbl->y() <= -(lbl->height())) {
                lbl->move(lbl->x(), this->height());
            }
            break;
        case Qt::Key_S:
            qDebug() << "Down";
            lbl->move(lbl->x(), lbl->y() + 20);
            if (lbl->y() >= this->height()) {
                lbl->move(lbl->x(), -lbl->height());
            }
            break;
        case Qt::Key_A:
            qDebug() << "Left";
            lbl->move(lbl->x() - 20, lbl->y());
            if (lbl->x() <= -(lbl->width())) {
                lbl->move(this->width(), lbl->y());
            }
            break;
        case Qt::Key_D:
            qDebug() << "Right";
            lbl->move(lbl->x() + 20, lbl->y());
            if (lbl->x() >= this->width()) {
                lbl->move(0, lbl->y());
            }
            break;

        case Qt::Key_B:
            qDebug() << "B";
            break;
        case Qt::Key_C:
            qDebug() << "C";
            break;

        default:
            break;
    }

    // 2. 两个按键
    if (event->modifiers() == Qt::ControlModifier &&
        event->key() == Qt::Key_A) {
        qDebug() << "Ctrl + A";
    }
    if (event->modifiers() == Qt::ShiftModifier && event->key() == Qt::Key_B) {
        qDebug() << "Shift + B";
    }
    if (event->modifiers() == Qt::AltModifier && event->key() == Qt::Key_C) {
        qDebug() << "Alt + C";
    }

    // 3. 三个按键
    if ((event->modifiers() == Qt::ControlModifier | Qt::ShiftModifier) &&
        event->key() == Qt::Key_A) {
        qDebug() << "Ctrl + Shift + A";
    }
}

void KeyWidget::keyReleaseEvent(QKeyEvent* event) {
    switch (event->key()) {
        case Qt::Key_Return:
            qDebug() << "keyReleaseEvent: Enter";
            break;
        case Qt::Key_Escape:
            qDebug() << "keyReleaseEvent: Esc";
            break;
        case Qt::Key_Control:
            qDebug() << "keyReleaseEvent: Ctrl";
            break;
        case Qt::Key_Shift:
            qDebug() << "keyReleaseEvent: Shift";
            break;
        case Qt::Key_Alt:
            qDebug() << "keyReleaseEvent: Alt";
            break;
        case Qt::Key_Up:
            qDebug() << "keyReleaseEvent: Up";
            break;
        case Qt::Key_Down:
            qDebug() << "keyReleaseEvent: Down";
            break;
        case Qt::Key_Left:
            qDebug() << "keyReleaseEvent: Left";
            break;
        case Qt::Key_Right:
            qDebug() << "keyReleaseEvent: Right";
            break;
        case Qt::Key_A:
            qDebug() << "keyReleaseEvent: A";
            break;
        case Qt::Key_B:
            qDebug() << "keyReleaseEvent: B";
            break;
        case Qt::Key_C:
            qDebug() << "keyReleaseEvent: C";
            break;
        case Qt::Key_D:
            qDebug() << "keyReleaseEvent: D";
            break;
        default:
            break;
    }
}
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2. 键盘事件移动标签

通过键盘的上下左右箭头，控制标签控件的上下

2.1 界面上添加标签

首先，在key_widget.h中添加成员变量：

// key_widget.h
private:
    QLabel *lbl;
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然后，在key_widget.cpp的构造中添加一个标签：

// key_widget.cpp
KeyWidget::KeyWidget(QWidget* parent) : QWidget{parent} {
    lbl = new QLabel(this);
    lbl->setFrameShape(QFrame::Box);
    lbl->setFixedSize(100, 100);
    lbl->setAlignment(Qt::AlignCenter);
    lbl->setStyleSheet("background-color: red");

    // 获取焦点
    setFocusPolicy(Qt::StrongFocus);
}
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2.2 移动标签

实现代码如下

void KeyWidget::keyPressEvent(QKeyEvent* event) {
    // 1. 单个按键
    switch (event->key()) {
        case Qt::Key_Return:
            qDebug() << "Enter";
            break;
        case Qt::Key_Escape:
            qDebug() << "Esc";
            break;
        case Qt::Key_Control:
            qDebug() << "Ctrl";
            break;
        case Qt::Key_Shift:
            qDebug() << "Shift";
            break;
        case Qt::Key_Alt:
            qDebug() << "Alt";
            break;
        case Qt::Key_W:
            qDebug() << "Up";
            lbl->move(lbl->x(), lbl->y() - 20);
            if (lbl->y() <= -(lbl->height())) {
                lbl->move(lbl->x(), this->height());
            }
            break;
        case Qt::Key_S:
            qDebug() << "Down";
            lbl->move(lbl->x(), lbl->y() + 20);
            if (lbl->y() >= this->height()) {
                lbl->move(lbl->x(), -lbl->height());
            }
            break;
        case Qt::Key_A:
            qDebug() << "Left";
            lbl->move(lbl->x() - 20, lbl->y());
            if (lbl->x() <= -(lbl->width())) {
                lbl->move(this->width(), lbl->y());
            }
            break;
        case Qt::Key_D:
            qDebug() << "Right";
            lbl->move(lbl->x() + 20, lbl->y());
            if (lbl->x() >= this->width()) {
                lbl->move(0, lbl->y());
            }
            break;

        case Qt::Key_B:
            qDebug() << "B";
            break;
        case Qt::Key_C:
            qDebug() << "C";
            break;

        default:
            break;
    }

    // 2. 两个按键
    if (event->modifiers() == Qt::ControlModifier &&
        event->key() == Qt::Key_A) {
        qDebug() << "Ctrl + A";
    }
    if (event->modifiers() == Qt::ShiftModifier && event->key() == Qt::Key_B) {
        qDebug() << "Shift + B";
    }
    if (event->modifiers() == Qt::AltModifier && event->key() == Qt::Key_C) {
        qDebug() << "Alt + C";
    }

    // 3. 三个按键
    if ((event->modifiers() == Qt::ControlModifier | Qt::ShiftModifier) &&
        event->key() == Qt::Key_A) {
        qDebug() << "Ctrl + Shift + A";
    }
}
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