Qt事件学习

一、创建Qt gui应用对应的源码：

点击(此处)折叠或打开

 //mylineedit.h
				#ifndef MYLINEEDIT_H
				#define MYLINEEDIT_H

				#include <QWidget>
				#include <QLineEdit>

				class MyLineEdit : public QLineEdit
				{
				public:
				    explicit MyLineEdit(QWidget *parent = 0);
				protected:
				    void keyPressEvent(QKeyEvent *event);
				};

				#endif // MYLINEEDIT_H


				//mylineedit.cpp
				#include "mylineedit.h"
				#include <QLineEdit>
				#include <QDebug>
				#include <QKeyEvent>

				MyLineEdit::MyLineEdit(QWidget *parent):QLineEdit(parent)
				{

				}

				void MyLineEdit::keyPressEvent(QKeyEvent *event)
				{
				    qDebug() << QObject::tr("MyLineEdit键盘按下事件");
				}

此时只会出现“MyLineEidt键盘按下事件”。

二、第二次修改

在mylineedit.cpp中keyPressEvent()添加

			event->ignore(); //忽略该事件

结果：多出现了"Widget键盘按下事件"，并且lineedit无法输入了。

三、第三次修改

在mylineedit.h中添加public函数：

			bool event(QEvent *event);

然后定义：

			bool MyLineEdit::event(QEvent *event)
			{
			    if(event->type() == QEvent::KeyPress)
			        qDebug()<<QObject::tr("MylineEdit的event()函数");
			    return QLineEdit::event(event);
			}

四、第四次修改

widget.h中public申明：

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

widget.cpp构造函数增加代码，并增加事件过滤器函数的定义：

			lineEdit->installEventFilter(this); //在widget上为lineEdit安装事件过滤器

			bool Widget::eventFilter(QObject *watched, QEvent *event)
			{
			    if(watched==lineEdit) {
			        if(event->type()==QEvent::KeyPress)
			            qDebug()<<QObject::tr("Widget的事件过滤器");
			    }
			    return QWidget::eventFilter(watched, event);
			}

五、最后的源码：
mylineedit:

			//mylineedit.h
			#ifndef MYLINEEDIT_H
			#define MYLINEEDIT_H

			#include <QWidget>
			#include <QLineEdit>

			class MyLineEdit : public QLineEdit
			{
			public:
			    explicit MyLineEdit(QWidget *parent = 0);
			    bool event(QEvent *event);

			protected:
			    void keyPressEvent(QKeyEvent *event);
			};

			#endif // MYLINEEDIT_H


			//mylineedit.cpp
			#include "mylineedit.h"
			#include <QLineEdit>
			#include <QDebug>
			#include <QKeyEvent>

			MyLineEdit::MyLineEdit(QWidget *parent):QLineEdit(parent)
			{

			}

			bool MyLineEdit::event(QEvent *event)
			{
			    if(event->type() == QEvent::KeyPress)
			        qDebug()<<QObject::tr("MylineEdit的event()函数");
			    return QLineEdit::event(event);
			}

			void MyLineEdit::keyPressEvent(QKeyEvent *event)
			{
			    qDebug() << QObject::tr("MyLineEdit键盘按下事件");
			    QLineEdit::keyPressEvent(event);
			    event->ignore();
			}

midget:

				//wdiget.h
				#ifndef WIDGET_H
				#define WIDGET_H

				#include <QWidget>

				class MyLineEdit;

				namespace Ui {
				class Widget;
				}

				class Widget : public QWidget
				{
				    Q_OBJECT

				public:
				    explicit Widget(QWidget *parent = 0);
				    ~Widget();
				    bool eventFilter(QObject *watched, QEvent *event);
				protected:
				    void keyPressEvent(QKeyEvent *event);
				private:
				    Ui::Widget *ui;
				    MyLineEdit *lineEdit;
				};

				#endif // WIDGET_H


				//widget.cpp
				#include "widget.h"
				#include "ui_widget.h"
				#include "mylineedit.h"
				#include <QKeyEvent>
				#include <QDebug>

				Widget::Widget(QWidget *parent) :
				    QWidget(parent),
				    ui(new Ui::Widget)
				{
				    lineEdit = new MyLineEdit(this);
				    lineEdit->move(100, 100);
				    lineEdit->installEventFilter(this); //在widget上为lineEdit安装事件过滤器
				    ui->setupUi(this);
				}

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

				bool Widget::eventFilter(QObject *watched, QEvent *event)
				{
				    if(watched==lineEdit) {
				        if(event->type()==QEvent::KeyPress)
				            qDebug()<<QObject::tr("Widget的事件过滤器");
				    }
				    return QWidget::eventFilter(watched, event);
				}

				void Widget::keyPressEvent(QKeyEvent *event)
				{
				    qDebug()<<QObject::tr("Widget键盘按下事件");
				}