Qt学习笔记（1）---QT5利用事件过滤器实现在控件上绘图

来源：互联网发布：2016年网络流行词汇编辑：程序博客网时间：2024/06/05 19:32

首先，感谢作者：一去丶二三里博客地址：http://blog.csdn.net/liang19890820

Qt中要在控件中绘制图像，需要重写paintevent函数，本文通过EventFilter(事件过滤器)来实现在控件上的图形绘制。

.h文件

#ifndef WIDGET_H#define WIDGET_H#include <QWidget>#include <QPointF>namespace Ui {class Widget;}class Widget : public QWidget{    Q_OBJECTpublic:    explicit Widget(QWidget *parent = 0);    ~Widget();public slots:    bool eventFilter(QObject *, QEvent *);private:    Ui::Widget *ui;    bool mouseIsdown;    QPointF startPos;    QPointF endPos;};#endif // WIDGET_H

.cpp文件

#include "widget.h"#include "ui_widget.h"#include <QPainter>#include <QMouseEvent>Widget::Widget(QWidget *parent) :    QWidget(parent),    ui(new Ui::Widget){    ui->setupUi(this);    mouseIsdown = false;    ui->label->installEventFilter(this);}Widget::~Widget(){    delete ui;}bool Widget::eventFilter(QObject *watched, QEvent *event){    if(watched == ui->label )    {        if(event->type() == QEvent::MouseButtonPress)        {            QMouseEvent *mouseEvent=(QMouseEvent *)event;            if(mouseEvent->buttons()&Qt::LeftButton)            {                mouseIsdown = true;                startPos = mouseEvent->pos();            }        }        if(event->type() == QEvent::MouseMove)        {            QMouseEvent *mouseEvent=(QMouseEvent *)event;            if(mouseIsdown)            {                endPos = mouseEvent->pos();                ui->label->update();            }        }        if(event->type() == QEvent::MouseButtonRelease)        {            QMouseEvent *mouseEvent=(QMouseEvent *)event;            endPos = mouseEvent->pos();            mouseIsdown = false;        }        if(event->type() == QEvent::Paint)        {            QPainter painter(ui->label);            QPen pen = painter.pen();            pen.setWidth(3);            pen.setColor(QColor(173, 255, 47));            //反走样            painter.setRenderHint(QPainter::Antialiasing, true);            painter.setPen(pen);            // 绘制直线            painter.drawLine(startPos, endPos);        }    }    return QWidget::eventFilter(watched,event);}

eventFilter(QObject *watched, QEvent *event)中

watched为事件过滤器的对象即本文中的label , event 为事件类型。

其中需要注意的有两点：

1.在构造函数中添加过滤器installEventFilter(this)如果一个控件添加了多个过滤器，后添加会被选择执行。

2.返回父类的eventfliterreturn QWidget::eventFilter(watched,event);

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