QT信号与槽实例

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/* widget.h*/#ifndef WIDGET_H#define WIDGET_H#include <QLabel>#include <QLineEdit>#include <QPushButton>#include <QtGui/QWidget>#include <QGridLayout>#include <QString>#include<QMessageBox>class Widget : public QWidget{    Q_OBJECT                //告诉QT 当前类中有自定义的槽函数public:    Widget(QWidget *parent = 0);    ~Widget();private:    QLabel *label1, *label2;    QLineEdit *lineEdit;    QPushButton *button;signals: void ss(QString);  //自定义信号private slots:    void showArea();        //自定义的槽函数声明    void showBox(QString);  //自定义的槽函数声明};#endif // WIDGET_H/* widget.cpp*/#include "widget.h"const static double PI = 3.1416;Widget::Widget(QWidget *parent)    : QWidget(parent){    label1 = new QLabel(this);    label1->setText(QString::fromLocal8Bit("请输入圆的半径："));    lineEdit = new QLineEdit(this);    label2 = new QLabel(this);    button = new QPushButton(this);    button->setText(QString::fromLocal8Bit("显示对应圆的面积"));    QGridLayout *mainLayout = new QGridLayout(this);    mainLayout->addWidget(label1,0,0);    mainLayout->addWidget(lineEdit,0,1);    mainLayout->addWidget(label2,1,0);    mainLayout->addWidget(button,1,1);    //connect(button,SIGNAL(clicked()),this,SLOT(close()));                //连接信号与槽函数    connect(button,SIGNAL(clicked()),this,SLOT(showArea()));               //连接信号与自定义槽函数    connect (lineEdit,SIGNAL(textChanged(QString)),this,SLOT(showArea())); //连接信号与自定义槽函数    connect(this,SIGNAL(ss(QString)),this,SLOT(showBox(QString)));         //连接自定义信号与自定义槽函数}Widget::~Widget(){}void Widget::showArea()    //自定义的槽函数定义{    bool ok;    QString tempStr;    QString valueStr = lineEdit->text();    int valueInt=valueStr.toInt(&ok);    double area=valueInt*valueInt*PI;    label2->setText(tempStr.setNum(area));    emit ss(QString::fromLocal8Bit("ShowArea执行了"));                    //发射信号}void Widget::showBox(QString a) //自定义的槽函数定义{    QMessageBox msgBox;    msgBox.setText(a);    msgBox.exec();}
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