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实现背景：
Qt本身有自己的QSlider，为什么我们还要自定义实现呢，因为Qt自带的QSlider存在一个问题，当首尾为圆角时，滑动滚动条到首尾时会出现圆角变成矩形的问题。当然如果QSS之间的margin和滑动条的圆角控制的好的话是不会出现这个问题的，但是我们一般都是按照美工设计来完成工作的，如果她的设计是必须一摸一样的话，这个margin和圆角配合不了出现以上问题的话，那我们就需要实现一个自定义的QSlider了。

实现思路：
1、继承QWidget或者QSlider都可以，当然如果我们继承QSlider的话，那还不如使用重写QStyle的方式来重绘。
2、使用paintevent绘制事件来进行重绘。
3、配合mouse鼠标事件实现拖动功能。
4、配合resizeEvent事件来实现自适应大小。

实现效果：

实现代码：
头文件：

#ifndef WIDGET_H
#define WIDGET_H#include <QWidget>
#include <QPainter>
#include <QMouseEvent>class Widget : public QWidget
{Q_OBJECTpublic:explicit Widget(QWidget *parent = nullptr);~Widget();void reset();   //复位void setDirection(int dire){m_direction = dire;}
protected:void mousePressEvent(QMouseEvent *event);void mouseMoveEvent(QMouseEvent *event);void mouseReleaseEvent(QMouseEvent *event);void resizeEvent(QResizeEvent *event);void paintEvent(QPaintEvent *event);
signals:void sig_Run();
private:QRect m_handleRect;bool m_pressFlag = false;bool m_autoFg = false;int m_lastX = 0;int m_lastY = 0;int m_direction = 0; //0:水平，1:垂直QPixmap m_handlepix;
};#endif // WIDGET_H

cpp文件：

#include "widget.h"
#include <QDebug>
Widget::Widget(QWidget *parent) :QWidget(parent)
{}Widget::~Widget()
{
}void Widget::resizeEvent(QResizeEvent *event)
{if (m_direction == 0)m_handleRect = QRect(1,1,height(),height() - 2);elsem_handleRect = QRect(1,height() - width(),width(),width() - 2);
}
void Widget::paintEvent(QPaintEvent *event)
{QPainter p(this);p.setRenderHint(QPainter::Antialiasing);p.setPen(QColor("#ffffff"));p.setBrush(QColor("#ffffff"));if (m_direction == 0)p.drawRoundedRect(this->rect(),height()/2,height()/2);elsep.drawRoundedRect(this->rect(),width()/2,width()/2);//滑轨前半部分QLinearGradient linearGradient(QPoint(0,0),QPoint(0,height()));linearGradient.setColorAt(0,QColor("#56B478"));linearGradient.setColorAt(0.7,QColor("#006009"));linearGradient.setColorAt(1,QColor("#56B478"));QBrush brush(linearGradient);p.setBrush(brush);if (m_direction == 0)p.drawRoundedRect(QRect(1,1,m_handleRect.right(),height()-2),height()/2,height()/2);elsep.drawRoundedRect(QRect(1,1,width(),m_handleRect.bottom()-2),width()/2,width()/2);//滑轨后半部分QBrush brush1(QColor("#606060"));p.setBrush(brush1);if (m_direction == 0)p.drawRoundedRect(QRect(m_handleRect.left(),1,width() - m_handleRect.left() - 2,height()-2),height()/2,height()/2);elsep.drawRoundedRect(QRect(1,m_handleRect.top(),width()-2,height() - m_handleRect.top()),width()/2,width()/2);//文本p.setPen(QColor("#ffffff"));p.setBrush(QColor("#ffffff"));p.setFont(QFont("Microsoft YaHei",8));p.drawText(2*width()/3,0,width()/3,height(),Qt::AlignCenter,"进度条");//滑动块//    p.drawPixmap(m_handleRect,m_handlepix);p.setPen(QColor("#ffffff"));p.setBrush(QColor("#842245"));p.drawEllipse(m_handleRect);
}void Widget::mousePressEvent(QMouseEvent *event)
{qDebug()<<m_handleRect<<event->pos();if (m_handleRect.contains(event->pos())){m_pressFlag = true;}}void Widget::mouseMoveEvent(QMouseEvent *event)
{if (m_pressFlag){if (m_direction == 0){int x = event->x();if (event->x() >= this->rect().right())x = this->rect().right() - 1;qDebug()<<x<<m_lastX<<width();if (x > this->rect().right() - m_handleRect.width())x = this->rect().right() - m_handleRect.width();if (x < 0)x = 0;m_handleRect = QRect(x,m_handleRect.y(),m_handleRect.width(),m_handleRect.height());if (m_autoFg){if (x > m_lastX && m_handleRect.right() >= this->rect().right() - width()/3){m_handleRect = QRect(this->rect().width() - m_handleRect.width() - 1,m_handleRect.y(),m_handleRect.width(),m_handleRect.height());}else if (m_handleRect.left() <= 0)m_handleRect = QRect(1,m_handleRect.y(),m_handleRect.width(),m_handleRect.height());m_lastX = x;}}else{int  y = event->y();if (event->y() >= this->rect().bottom())y = this->rect().bottom() - 1;if (y > this->rect().bottom() - m_handleRect.height())y = this->rect().bottom() - m_handleRect.height();if (y < 0)y = 0;m_handleRect = QRect(m_handleRect.x(),y,m_handleRect.width(),m_handleRect.height());if (m_autoFg){if (y < m_lastY && m_handleRect.top() <= height()/3){m_handleRect = QRect(m_handleRect.x(),1,m_handleRect.width(),m_handleRect.height());}m_lastY = y;}}update();}
}void Widget::mouseReleaseEvent(QMouseEvent *event)
{//autoif (m_autoFg){if (m_handleRect.right() != this->rect().right() - 1){m_handleRect = QRect(1,m_handleRect.y(),m_handleRect.width(),m_handleRect.height());update();}else {emit sig_Run();}}elseemit sig_Run();m_pressFlag = false;}void Widget::reset()
{m_handleRect = QRect(1,m_handleRect.y(),m_handleRect.width(),m_handleRect.height());update();
}