Qt利用Qss和QPainter实现各种漂亮精美的导航条

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索鸟 2021-03-18

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导航按钮控件，主要用于各种漂亮精美的导航条，我们经常在web中看到导航条都非常精美，都是html+css+js实现的，还自带动画过度效果，Qt提供的qss其实也是无敌的，支持基本上所有的CSS2属性，配合QPainter这个无敌大法工具，没有什么不能绘制的。这个控件总结了大部分的导航条样式，比如左侧+右侧+顶部+底部，线条指示器，倒三角指示器等。还可以在导航条前面加上图标等，就显得更加有特色。有了此控件，再也不用担心没有精美的导航了。总之这个控件在我的很多的项目中都在用，而且很多Qt界的朋友也在用，反响很热烈很好。

主要功能：
1. 可设置文字的左侧+右侧+顶部+底部间隔
2. 可设置文字对齐方式
3. 可设置显示倒三角/倒三角边长/倒三角位置/倒三角颜色
4. 可设置显示图标/图标间隔/图标尺寸/正常状态图标/悬停状态图标/选中状态图标
5. 可设置显示边框线条/线条宽度/线条间隔/线条位置/线条颜色
6. 可设置正常背景颜色/悬停背景颜色/选中背景颜色
7. 可设置正常文字颜色/悬停文字颜色/选中文字颜色
8. 可设置背景颜色为画刷颜色

## 二、代码思路
```c++
void NavButton::paintEvent(QPaintEvent *)
{
    //绘制准备工作,启用反锯齿
    QPainter painter(this);
    painter.setRenderHints(QPainter::Antialiasing | QPainter::TextAntialiasing);

    //绘制背景
    drawBg(&painter);
    //绘制文字
    drawText(&painter);
    //绘制图标
    drawIcon(&painter);
    //绘制边框线条
    drawLine(&painter);
    //绘制倒三角
    drawTriangle(&painter);
}

void NavButton::drawBg(QPainter *painter)
{
    painter->save();
    painter->setPen(Qt::NoPen);

    int width = this->width();
    int height = this->height();

    QRect bgRect;
    if (linePosition == LinePosition_Left) {
        bgRect = QRect(lineSpace, 0, width - lineSpace, height);
    } else if (linePosition == LinePosition_Right) {
        bgRect = QRect(0, 0, width - lineSpace, height);
    } else if (linePosition == LinePosition_Top) {
        bgRect = QRect(0, lineSpace, width, height - lineSpace);
    } else if (linePosition == LinePosition_Bottom) {
        bgRect = QRect(0, 0, width, height - lineSpace);
    }

    //如果画刷存在则取画刷
    QBrush bgBrush;
    if (isChecked()) {
        bgBrush = checkBgBrush;
    } else if (hover) {
        bgBrush = hoverBgBrush;
    } else {
        bgBrush = normalBgBrush;
    }

    if (bgBrush != Qt::NoBrush) {
        painter->setBrush(bgBrush);
    } else {
        //根据当前状态选择对应颜色
        QColor bgColor;
        if (isChecked()) {
            bgColor = checkBgColor;
        } else if (hover) {
            bgColor = hoverBgColor;
        } else {
            bgColor = normalBgColor;
        }

        painter->setBrush(bgColor);
    }

    painter->drawRect(bgRect);

    painter->restore();
}

void NavButton::drawText(QPainter *painter)
{
    painter->save();
    painter->setBrush(Qt::NoBrush);

    //根据当前状态选择对应颜色
    QColor textColor;
    if (isChecked()) {
        textColor = checkTextColor;
    } else if (hover) {
        textColor = hoverTextColor;
    } else {
        textColor = normalTextColor;
    }

    QRect textRect = QRect(paddingLeft, paddingTop, width() - paddingLeft - paddingRight, height() - paddingTop - paddingBottom);
    painter->setPen(textColor);
    painter->drawText(textRect, textAlign | Qt::AlignVCenter, text());

    painter->restore();
}

void NavButton::drawIcon(QPainter *painter)
{
    if (!showIcon) {
        return;
    }

    painter->save();

    QPixmap pix;
    if (isChecked()) {
        pix = iconCheck;
    } else if (hover) {
        pix = iconHover;
    } else {
        pix = iconNormal;
    }

    if (!pix.isNull()) {
        //等比例平滑缩放图标
        pix = pix.scaled(iconSize, Qt::KeepAspectRatio, Qt::SmoothTransformation);
        painter->drawPixmap(iconSpace, (height() - iconSize.height()) / 2, pix);
    }

    painter->restore();
}

void NavButton::drawLine(QPainter *painter)
{
    if (!showLine) {
        return;
    }

    if (!isChecked()) {
        return;
    }

    painter->save();

    QPen pen;
    pen.setWidth(lineWidth);
    pen.setColor(lineColor);
    painter->setPen(pen);

    //根据线条位置设置线条坐标
    QPoint pointStart, pointEnd;
    if (linePosition == LinePosition_Left) {
        pointStart = QPoint(0, 0);
        pointEnd = QPoint(0, height());
    } else if (linePosition == LinePosition_Right) {
        pointStart = QPoint(width(), 0);
        pointEnd = QPoint(width(), height());
    } else if (linePosition == LinePosition_Top) {
        pointStart = QPoint(0, 0);
        pointEnd = QPoint(width(), 0);
    } else if (linePosition == LinePosition_Bottom) {
        pointStart = QPoint(0, height());
        pointEnd = QPoint(width(), height());
    }

    painter->drawLine(pointStart, pointEnd);

    painter->restore();
}

void NavButton::drawTriangle(QPainter *painter)
{
    if (!showTriangle) {
        return;
    }

    //选中或者悬停显示
    if (!hover && !isChecked()) {
        return;
    }

    painter->save();
    painter->setPen(Qt::NoPen);
    painter->setBrush(triangleColor);

    //绘制在右侧中间,根据设定的倒三角的边长设定三个点位置
    int width = this->width();
    int height = this->height();
    int midWidth = width / 2;
    int midHeight = height / 2;

    QPolygon pts;
    if (trianglePosition == TrianglePosition_Left) {
        pts.setPoints(3, triangleLen, midHeight, 0, midHeight - triangleLen, 0, midHeight + triangleLen);
    } else if (trianglePosition == TrianglePosition_Right) {
        pts.setPoints(3, width - triangleLen, midHeight, width, midHeight - triangleLen, width, midHeight + triangleLen);
    } else if (trianglePosition == TrianglePosition_Top) {
        pts.setPoints(3, midWidth, triangleLen, midWidth - triangleLen, 0, midWidth + triangleLen, 0);
    } else if (trianglePosition == TrianglePosition_Bottom) {
        pts.setPoints(3, midWidth, height - triangleLen, midWidth - triangleLen, height, midWidth + triangleLen, height);
    }

    painter->drawPolygon(pts);

    painter->restore();
}
```

## 三、效果图

原文地址：http://www.qtcn.org/bbs/read-htm-tid-88631-ds-1.html

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