Qt在子部件上绘图

 

本文记录如何使用qpainter在子部件上绘图。

1.需要在子部件上安装事件过滤器

frame->installEventFilter(this); //安装事件过滤器到窗口

2.头文件中声明如下

bool eventFilter(QObject *watched, QEvent *event);

bool m_flag=false;//绘图标志

3.声明画图函数

void graphChart(QWidget *w);

4.如果使用按钮来控制画图

m_flag = true;
update();

代码展示如下：

头文件：

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include<QPaintEvent>
#include<QPainter>
namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = nullptr);
    ~MainWindow();
//    void paintEvent(QPaintEvent *p);
    QPainter *painter;

private slots:
    void on_pushButton_clicked();

private:
    Ui::MainWindow *ui;
    bool m_flag = false;//绘图标志
    bool eventFilter(QObject *watched, QEvent *event);
    void graphChart(QWidget *w);
};

#endif // MAINWINDOW_H

Cpp文件 ：

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    ui->widget->installEventFilter(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}



void MainWindow::on_pushButton_clicked()
{
    m_flag = true;
    update();
}

bool MainWindow::eventFilter(QObject *watched, QEvent *event)
{
    if(watched ==ui->widget&&event->type()==QEvent::Paint)
    {
        graphChart(ui->widget);
    }

    return QWidget::eventFilter(watched,event);
}

void MainWindow::graphChart(QWidget *w)
{
    if(m_flag)
    {
        painter = new QPainter();
        painter->begin(w);
        QPen pen;
        pen.setColor(Qt::red);
        painter->setPen(pen);
        painter->drawText(100,100,"Paintevent");
        painter->end();

    }

}

补充：

画了个等边三角形 

void MainWindow::drawTriangle(QPainter *painter)
{
    painter->save();
    double radius =100;
    painter->setPen(Qt::NoPen);
    static const QPointF points[3]={QPointF(radius,0),QPointF(0,0),QPointF(radius/2,sqrt(pow(radius,2)-pow(radius/2,2)))};
    
    painter->setBrush(Qt::red);
    painter->drawConvexPolygon(points,3);
    painter->restore();
}

 

5.源码下载

https://download.youkuaiyun.com/download/weixin_41882459/12034948