自定义的Qt搜索框控件

class MSearchBar : public QWidget
{
    Q_OBJECT

public:
    MSearchBar(QWidget* parent = 0);
    QSize sizeHint() const override;

signals:
    void inputCompleted(const QString& str);

private slots:
    void leTextReturnPressed();

private:
    void addHistory(const QString& str);
    bool eventFilter(QObject *watched, QEvent *event) override;
    void paintEvent(QPaintEvent*) override;
    void resizeEvent(QResizeEvent *event) override;
    void mouseMoveEvent(QMouseEvent *event) override;
    void mousePressEvent(QMouseEvent *event) override;
    void mouseReleaseEvent(QMouseEvent *event) override;
    void enterEvent(QEvent *event) override;
    void leaveEvent(QEvent *event) override;
    void showPopup();

    enum Status
    {
        NONE,
        HOVERED,
        PRESSED,
    };

private:
    class MDiyListWidget;
    bool focused;
    bool oddClick;
    Status state;
    QPoint pressPt;
    QRect magnifier;
    QStringList history;
    QLineEdit* leText;
    MDiyListWidget* lwList;
};

class QListWidget;

class MSearchBar::MDiyListWidget : public QWidget
{
    Q_OBJECT

public:
    MDiyListWidget(QWidget* parent = 0);
    void setItems(const QStringList& strs);

signals:
    void textChanged(const QString&);

private slots:
    void lwListItemSelectionChanged();

private:
    QListWidget* lwList;
};

MSearchBar::MSearchBar(QWidget* parent) :
    QWidget(parent), focused(false), state(NONE)
{
    oddClick = false;
    setMouseTracking(true);

    QHBoxLayout* lay = new QHBoxLayout(this);
    leText = new QLineEdit(this);
    leText->setStyleSheet(u8"QLineEdit { border:none; }");
    leText->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Preferred);
    leText->installEventFilter(this);
    lay->addWidget(leText);
    setLayout(lay);
    connect(leText, &QLineEdit::returnPressed, this, &MSearchBar::leTextReturnPressed);
    lwList = new MDiyListWidget(this);
    connect(lwList, &MDiyListWidget::textChanged, leText, &QLineEdit::setText);
}

void MSearchBar::leTextReturnPressed()
{
    QString str = leText->text();
    emit inputCompleted(str);
    addHistory(str);
}

void MSearchBar::addHistory(const QString& str)
{
    if (!str.isEmpty() && !history.contains(str))
    {
        history.append(str);
    }
    if (history.size() > 10)
    {
        history.pop_front();
    }
}

void MSearchBar::resizeEvent(QResizeEvent *event)
{
    QSize sz = event->size();
    layout()->setContentsMargins(1, 1, sz.height() - 1, 1);
    magnifier.setX(sz.width() - sz.height() + 1);
    magnifier.setY(1);
    magnifier.setWidth(sz.height() - 2);
    magnifier.setHeight(sz.height() - 2);
}

void MSearchBar::paintEvent(QPaintEvent*)
{
    QStyleOption opt;
    opt.init(this);
    QPainter painter(this);
    style()->drawPrimitive(QStyle::PE_Widget, &opt, &painter, this);
    QPalette pale = palette();
    painter.setBrush(Qt::NoBrush);
    /* 绘制边框 */
    if (focused)
    {
        painter.setPen(QPen(pale.highlight(), 1));
        painter.drawRect(0, 0, width() - 1, height() - 1);
    }
    else
    {
        painter.setPen(QPen(pale.mid(), 1));
        painter.drawRect(0, 0, width() - 1, height() - 1);
    }
    /* 绘制放大镜 */
    const QPointF ciCenter(0.4, 0.4);
    const qreal ciRadius = 0.2;
    const QPointF liStart(0.6, 0.6);
    const QPointF liEnd(0.83, 0.83);
    painter.setRenderHint(QPainter::Antialiasing);
    switch (state)
    {
    case MSearchBar::NONE:
        painter.translate(magnifier.x(), magnifier.y());
        painter.setPen(QPen(pale.mid(), 2));
        break;
    case MSearchBar::HOVERED:
        painter.fillRect(magnifier, pale.highlight());
        painter.translate(magnifier.x(), magnifier.y());
        painter.setPen(QPen(pale.light(), 2));
        break;
    case MSearchBar::PRESSED:
        painter.fillRect(magnifier, pale.highlight());
        painter.translate(magnifier.x() + 1, magnifier.y() + 1);
        painter.setPen(QPen(pale.light(), 2));
        break;
    default: // never goto this.
        break;
    }
    int msz = magnifier.width();
    painter.drawEllipse(ciCenter * msz, ciRadius * msz, ciRadius * msz);
    painter.drawLine(msz * liStart, msz * liEnd);
}

bool MSearchBar::eventFilter(QObject *watched, QEvent *event)
{
    if (event->type() == QEvent::FocusIn)
    {
        focused = true;
        update();
    }
    else if (event->type() == QEvent::FocusOut)
    {
        focused = false;
        update();
    }
    else if (event->type() == QEvent::MouseMove && state == HOVERED)
    {
        state = NONE;
        update();
    }
    else if (event->type() == QEvent::MouseButtonRelease)
    {
        QMouseEvent* mouseEvent = dynamic_cast<QMouseEvent*>(event);
        if (mouseEvent->button() == Qt::LeftButton)
        {
            oddClick = !oddClick;
            if (!history.empty() && oddClick)
            {
                showPopup();
            }
        }
    }
    return false;
}

void MSearchBar::showPopup()
{
    lwList->setItems(history);
    QPoint scrPos = mapToGlobal(QPoint(0, height()));
    lwList->move(scrPos);
    lwList->setFixedWidth(width());
    lwList->show();
}

void MSearchBar::mouseMoveEvent(QMouseEvent *event)
{
    bool isHover = magnifier.contains(event->pos());
    if (isHover && state != HOVERED)
    {
        state = HOVERED;
        update();
    }
    else if (!isHover && state != NONE)
    {
        state = NONE;
        update();
    }
}

void MSearchBar::mousePressEvent(QMouseEvent *event)
{
    QPoint p = event->pos();
    if (magnifier.contains(p))
    {
        pressPt = p;
        state = PRESSED;
        update();
    }
}

void MSearchBar::mouseReleaseEvent(QMouseEvent *event)
{
    if (pressPt == event->pos())
    {
        state = HOVERED;
        QString str = leText->text();
        emit inputCompleted(str);
        addHistory(str);
        update();
    }
}

void MSearchBar::enterEvent(QEvent *event)
{
    // nothing.
}

void MSearchBar::leaveEvent(QEvent *event)
{
    state = NONE;
    update();
}

QSize MSearchBar::sizeHint() const
{
    return QSize(160, 24);
}

/////////////////////////////////////////////////////////////////////////////////////////

MSearchBar::MDiyListWidget::MDiyListWidget(QWidget* parent) :
    QWidget(parent)
{
    setWindowFlag(Qt::Popup);

    QHBoxLayout* lay = new QHBoxLayout(this);
    lay->setContentsMargins(0, 0, 0, 0);
    lwList = new QListWidget(this);
    lay->addWidget(lwList);
    setLayout(lay);
    connect(lwList, &QListWidget::itemSelectionChanged, this, &MDiyListWidget::lwListItemSelectionChanged);
}

void MSearchBar::MDiyListWidget::setItems(const QStringList& strs)
{
    lwList->clear();
    lwList->addItems(strs);
}

void MSearchBar::MDiyListWidget::lwListItemSelectionChanged()
{
    QList<QListWidgetItem*> selects = lwList->selectedItems();
    if (!selects.empty())
    {
        emit textChanged(selects.first()->text());
        close();
    }
}