QT简单实例计算圆的面积

注：本文部分或全部内容摘自《Qt5开发及实例 陆文周 主编》

dialog.h

#ifndef DIALOG_H
#define DIALOG_H

#include <QDialog>
#include <QLabel>
#include <QPushButton>
#include <QLineEdit>
#include <QWidget>
#include <QSerialPort>
#include <QSerialPortInfo>

class Dialog : public QDialog
{
    
    
    //Q_OBJECT 宏的作用是启动Qt元对象系统的一些特性（如：支持信号和槽），必须放到类定义的私有区；
    Q_OBJECT
public:
    Dialog(QWidget *parent = nullptr);
    ~Dialog();
private:
    // 控件变量指针
    QLabel *label1, *label2;
    QLineEdit *lineEdit;
    QPushButton *button;
    QSerialPort *serial;

private slots: //信号槽方法接口
    void showArea();
};

#endif // DIALOG_H

dialog.cpp

#include <QLabel>
#include <QLineEdit>
#include <QPushButton>
#include <QGridLayout>

#include <QList>
#include <QMap>
#include <QHash>
#include <QLinkedList>
#include <QVector>



#include "dialog.h"
const static double PI = 3.1415926;

// Dialog类构造方法
Dialog::Dialog(QWidget *parent):QDialog(parent)
{
    
    
    // 创建控件实例
    label1 = new QLabel(this);
    label1->setText(tr("请输入半径："));
    lineEdit = new QLineEdit(this);
    label2 = new QLabel(this);
    label2->setText(tr("面积"));
    button = new QPushButton(this);
    button->setText(tr("计算"));

    // 添加控制到指定布局
    QGridLayout *gridLayout = new QGridLayout(this);
    gridLayout->addWidget(label1, 0, 0);
    gridLayout->addWidget(lineEdit, 0, 1);
    gridLayout->addWidget(label2, 1, 0);
    gridLayout->addWidget(button, 1, 1);

    // 连接信号槽
    connect(button, SIGNAL(clicked()), this, SLOT(showArea()));
    connect(lineEdit, SIGNAL(textChanged()), this, SLOT(showArea()));
};

// Dialog析构方法
Dialog::~Dialog()
{
    
    
    delete(label1);
    delete(label2);
    delete(lineEdit);
    delete(button);
};

// 信号槽功能实现
void Dialog::showArea()
{
    
    
    bool ok;
    QString tempStr;
    QString valueStr = lineEdit->text();
    int valueInt = valueStr.toInt(&ok);
    double area = valueInt * valueInt * PI;
    label2->setText(tempStr.setNum(area));
    qDebug("tempStr:%s", tempStr.toStdString().c_str());
};

mainwindow.h

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

QT_BEGIN_NAMESPACE
namespace Ui {
    
     class MainWindow; }
QT_END_NAMESPACE

class MainWindow : public QMainWindow
{
    
    
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);
    ~MainWindow();

private slots:
    void on_pushButton_clicked();

    void on_radiusLineEdit_textChanged(const QString &arg1);

private:
    Ui::MainWindow *ui;
};
#endif // MAINWINDOW_H

mainwindow.cpp

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

const static double PI = 3.1415926;
//const static double E = 2.71828;
//const static double S2 = 1.414;
//const static double FI = 0.618;


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

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

// UI添加信号槽
void MainWindow::on_pushButton_clicked()
{
    
    
    bool ok;
    qDebug("on pushbutton clicked");
    QString tempStr;
    QString valueStr = ui->radiusLineEdit->text();
    int valueInt = valueStr.toInt(&ok);
    double area = valueInt * valueInt *PI; //
    ui->valueLineEdit->setText(tempStr.setNum(area));
}

// UI添加信号槽
void MainWindow::on_radiusLineEdit_textChanged(const QString &arg1)
{
    
    
    bool ok;
    qDebug("on lineedit textchanged");
    QString tempStr;
    QString valueStr = ui->radiusLineEdit->text();
    int valueInt = valueStr.toInt(&ok);
    double area = valueInt * valueInt * PI;
    ui->valueLineEdit->setText(tempStr.setNum(area));
}

main.cpp

#include "mainwindow.h"
#include "dialog.h"

#include <QApplication>
#include <QLabel>
#include <QButtonGroup>
#include <QPushButton>
#include <QWidget>
#include <QVBoxLayout>

#include <QFile>



int main(int argc, char *argv[])
{
    
    
    QApplication app(argc, argv);
    MainWindow win;
    win.show();

    Dialog dialog;
    dialog.show(); // 显示Dialog对话框


    #if 0//代码实现控件,因为控制没有指定父窗口window, 所以创建控件都是在独立窗口显示
    QLabel label("hello word");
    label.setText("Hello Word new text!");
    label.show();

    QLabel *label2 = new QLabel("Label 2");
    label2->setAttribute(Qt::WA_DeleteOnClose);
    label2->show();

    QPushButton button("Quit");
    QObject::connect(&button, &QPushButton::clicked, &QApplication::quit);
    button.show();
    #endif

    return app.exec();
}

运行效果：
![在这里插入图片描述](https://img-blog.csdnimg.cn/20201021181854250.gif#pic_center)
添加链接描述