QT 绘图与重绘事件

代码实现仪表盘

.cpp

#include "widget.h"
#include "ui_widget.h"#include <QPainter>
#include <QPen>
#include <QBrush>#include <QDebug>
Widget::Widget(QWidget *parent): QWidget(parent), ui(new Ui::Widget)
{ui->setupUi(this);ui->Slidersudu->setMaximum(300);ui->Slidersudu->setMinimum(0);connect(ui->Slidersudu,SIGNAL(valueChanged(int)),this,SLOT(hSliderValueChangedSlot(int)));
}Widget::~Widget()
{delete ui;
}void Widget::paintEvent(QPaintEvent *event)
{QPainter p (this);p.translate( this->width()/2, this->height()/2);QBrush brush; brush.setColor(QColor(0,42,79));  brush.setStyle(Qt::SolidPattern);p.setBrush(brush);p.drawEllipse(-200,-200,400,400); //drawEllipse(x,y,w,h) 圆QBrush brush2; brush.setColor(QColor(0,0,0));  brush.setStyle(Qt::SolidPattern);p.setBrush(brush);p.drawEllipse(-175,-175,350,350);QBrush brush3; brush.setColor(QColor(0,180,150));  brush.setStyle(Qt::SolidPattern);p.setBrush(brush);p.drawEllipse(-75,-75,150,150);QBrush brush4; brush.setColor(QColor(0,0,0));  brush.setStyle(Qt::SolidPattern);p.setBrush(brush);p.drawEllipse(-40,-40,80,80);//划线p.rotate(120);QPen pen; pen.setColor( QColor(0,255,50));  pen.setWidth(3); pen.setStyle(Qt::SolidLine);p.setPen(pen);int log = 0;for(int i = 6;;){p.rotate(i);log++;if(log == 50){break;}if(log%2 == 0){p.drawLine(120,0,140,0);}else if(log%2 != 0){p.drawLine(110,0,140,0);}}p.rotate(60);p.rotate( ui->Slidersudu->value() );QPen pen2;pen2.setColor(QColor(255,0,0));pen2.setWidth(3);pen2.setStyle(Qt::SolidLine);p.setPen(pen2);p.drawLine(0,0,this->width()/3,0);this->update();
}void Widget::hSliderValueChangedSlot(int)
{qDebug()<<__func__;this->update();
}

#ifndef WIDGET_H
#define WIDGET_H#include <QWidget>QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACEclass Widget : public QWidget
{Q_OBJECTpublic:Widget(QWidget *parent = nullptr);~Widget();void paintEvent(QPaintEvent *event) override;void hSliderValueChangedSlot(int);private:Ui::Widget *ui;
};
#endif // WIDGET_H

现象