QT message mechanism and events
The event goes through the following: event distribution ------> event filter --------> event distribution --------> event processing stage
event() event distribution function
1. Commonly used event functions:
View the help documentation to view events;
a bunch of events;
2. Window close reset and size event function
#ifndef WIDGET_H
#define WIDGET_H
#include <QWidget>
QT_BEGIN_NAMESPACE
namespace Ui { class Widget; }
QT_END_NAMESPACE
class Widget : public QWidget
{
Q_OBJECT
public:
Widget(QWidget *parent = nullptr);
~Widget();
//重写函数声明
protected:
void closeEvent(QCloseEvent *event);
void resizeEvent(QResizeEvent *event);
private:
Ui::Widget *ui;
};
#endif // WIDGET_H
#include "widget.h"
#include "ui_widget.h"
#include <QMessageBox>
#include <QCloseEvent>
#include <QDebug>
Widget::Widget(QWidget *parent)
: QWidget(parent)
, ui(new Ui::Widget)
{
ui->setupUi(this);
}
Widget::~Widget()
{
delete ui;
}
void Widget::closeEvent(QCloseEvent *event){
int ret=QMessageBox::question(this,"提示","确定您要关闭窗口吗？");
if(ret==QMessageBox::Yes){
event->accept(); //处理
}else{
event->ignore(); //忽略
}
}
void Widget::resizeEvent(QResizeEvent *event){
qDebug()<<event->oldSize();
qDebug()<<event->size();
}
3. Mouse click release move event
First create a Label, create a class to inherit QLabel, promote the established Label to the established QLabel, and overload the mouse function in the established QLabel
#ifndef MYLABEL_H
#define MYLABEL_H
#include <QDebug>
#include <QLabel>
class MyLabel : public QLabel
{
Q_OBJECT
public:
explicit MyLabel(QWidget *parent = nullptr);
signals:
public slots:
protected:
//鼠标按下事件
void mousePressEvent(QMouseEvent *ev);
void mouseReleaseEvent(QMouseEvent *ev);
void mouseMoveEvent(QMouseEvent *ev);
};
#endif // MYLABEL_H
#include "mylabel.h"
MyLabel::MyLabel(QWidget *parent) : QLabel(parent)
{
this->setMouseTracking(true);
}
void MyLabel::mousePressEvent(QMouseEvent *ev){
qDebug()<<"标签被按下";
}
void MyLabel::mouseReleaseEvent(QMouseEvent *ev){
qDebug()<<"标签被抬起";
}
void MyLabel::mouseMoveEvent(QMouseEvent *ev){
qDebug()<<"移动";
}
#include "mylabel.h"
#include <QMouseEvent>
MyLabel::MyLabel(QWidget *parent) : QLabel(parent)
{
this->setMouseTracking(true);
}
void MyLabel::mousePressEvent(QMouseEvent *ev){
if(ev->button()==Qt::LeftButton){
qDebug()<<"左键被按下";
}else if(ev->button()==Qt::RightButton){
qDebug()<<"右键被按下";
}else{
qDebug()<<"标签被按下";
}
}
void MyLabel::mouseReleaseEvent(QMouseEvent *ev){
qDebug()<<"标签被抬起";
}
void MyLabel::mouseMoveEvent(QMouseEvent *ev){
qDebug()<<"移动"<<ev->x()<<","<<ev->y();
QString str;
str.sprintf("<center><h1>(%d,%d)</h1><center>",ev->x(),ev->y());
this->setText(str);
}
3. Rewrite the time distribution function
#include "widget.h"
#include "ui_widget.h"
#include <QMessageBox>
#include <QCloseEvent>
#include <QDebug>
Widget::Widget(QWidget *parent)
: QWidget(parent)
, ui(new Ui::Widget)
{
ui->setupUi(this);
}
Widget::~Widget()
{
delete ui;
}
void Widget::closeEvent(QCloseEvent *event){
int ret=QMessageBox::question(this,"提示","确定您要关闭窗口吗？");
if(ret==QMessageBox::Yes){
event->accept(); //处理
}else{
event->ignore(); //忽略
}
}
void Widget::resizeEvent(QResizeEvent *event){
qDebug()<<event->oldSize();
qDebug()<<event->size();
}
bool Widget::event(QEvent *event){
//判断是否是键盘事件
if(event->type()==QEvent::KeyPress){
//将QEvent类型的event转换成QKeyEvent
QKeyEvent *keyevent=static_cast<QKeyEvent *>(event);
if(keyevent->key()==Qt::Key_Tab){
qDebug()<<"TAB被按下";
return true;
}
}
//返回父对象
return QWidget::event(event);
}
4. Brush use
·
#include "widget.h"
#include "ui_widget.h"
#include <QPaintEvent>
#include <QDebug>
#include <QPainter>
Widget::Widget(QWidget *parent)
: QWidget(parent)
, ui(new Ui::Widget)
{
ui->setupUi(this);
this->setFixedSize(800,600);
}
Widget::~Widget()
{
delete ui;
}
void Widget::paintEvent(QPaintEvent *p){//页面加载，update执行
QPainter painter(this);
//定义一个画笔
painter.drawLine(80,100,500,500);
//画一条直线
painter.setPen(Qt::red);
//设置线为红色
painter.drawRect(0,0,400,200);
//画一个矩形，0,0代表开始坐标，100,400代表宽度和高度
painter.setPen(QPen(Qt::blue,5));
//设置颜色为蓝色，粗细为5
painter.drawEllipse(0,0,400,200);
//画一个圆
}
Qpainter: There are various drawing functions in it
Drawing device:
