前言

  本篇通过提升法实现一个动态圆形进度条。

一、需求

  自定义实现一个动态圆形进度条，支持设置进度条颜色、目标值背景色、外边框背景色、中央圆环背景色、旋转角度及大小自适应缩放。同时，支持设置范围值和单位，满足不同场景需要。
  效果如下：

二、实现

1、自定义控件类

新建一个自定义控件类，类名为RoundPlot，继承于QWidget类，该类主要负责实现自定义控件。
核心代码如下：

void RoundPlot::drawDial(QPainter *painter)
{
    int radius = 95;
    double lineWidth = 2.5;
    painter->save();
    painter->rotate(angle);

    //根据起始旋转的角度计算每次坐标需要旋转的角度,按照100等分计算
    //每次旋转的角度=360-(起始角度*2--分左右)/100
    double rotate = (double)(360 - (angle * 2)) / 100;

    //绘制已使用百分比
    painter->setPen(QPen(usedColor, lineWidth));

    for (double i = 0; i < currentPercent; i++) {
        painter->drawLine(0, radius, 0, radius / 1.2);
        painter->rotate(rotate);
    }

    //绘制未使用百分比
    painter->setPen(QPen(freeColor, lineWidth));

    for (double i = currentPercent; i < 100; i++) {
        painter->drawLine(0, radius, 0, radius / 1.2);
        painter->rotate(rotate);
    }

    painter->restore();
}

void RoundPlot::drawBgOut(QPainter *painter)
{
    int radius = 70;
    painter->save();
    painter->setPen(Qt::NoPen);
    painter->setBrush(outBgColor);
    painter->drawEllipse(-radius, -radius, radius * 2, radius * 2);
    painter->restore();
}

void RoundPlot::drawBgRound(QPainter *painter)
{
    int radius = 50;
    painter->save();
    QConicalGradient conicalGradient(radius, radius, 90);
    conicalGradient.setColorAt(0, centerBgColorStart);
    conicalGradient.setColorAt(1.0, centerBgColorEnd);
    painter->setPen(Qt::NoPen);
    painter->setBrush(conicalGradient);
    painter->drawEllipse(-radius, -radius, radius * 2, radius * 2);
    painter->restore();
}

void RoundPlot::drawBgCenter(QPainter *painter)
{
    int radius = 30;
    painter->save();
    painter->setPen(Qt::NoPen);
    painter->setBrush(valueBgColor);
    painter->drawEllipse(-radius, -radius, radius * 2, radius * 2);
    painter->restore();
}

void RoundPlot::drawText(QPainter *painter)
{
    int radius = 100;
    painter->save();

    //绘制百分比文字及范围值文字
    double currentValue = currentPercent * ((maxValue - minValue) / 100) + minValue;

    //如果当前值超过了目标值则取目标值
    if (currentValue > value) {
        currentValue = value;
    }

    QString strValue = QString("%1%2").arg(QString::number(currentValue, 'f', precision)).arg(unit);
    QString strMinValue = QString("%1%2").arg(minValue).arg(unit);
    QString strMaxValue = QString("%1%2").arg(maxValue).arg(unit);

    painter->setFont(QFont("Arial", 13));
    painter->setPen(QPen(valueTextColor));
    QFontMetricsF fm = QFontMetricsF(painter->font());
    QSizeF size = fm.size(Qt::TextSingleLine, strValue);
    painter->drawText(-size.width() / 2, size.height() / 3, strValue);

    painter->setFont(QFont("Arial", 8));
    painter->setPen(QPen(rangeTextColor));
    fm = QFontMetricsF(painter->font());
    size = fm.size(Qt::TextSingleLine, strMinValue);
    painter->drawText(-radius / 2 - size.width() / 2 + 8, 80, strMinValue);
    size = fm.size(Qt::TextSingleLine, strMaxValue);
    painter->drawText(radius / 2 - size.width() / 2 - 8, 80, strMaxValue);

    painter->restore();
}

2、提升

在设计师中，将widget控件提升为RoundPlot，如下：

3、效果

编译运行后，效果如下：