Qt学习笔记1_搭建一个基本窗口实现计算圆的面积

这里记录下Qt的学习过程：

先注明一下环境：Qt5.9.2+VS2015

在VS新建项目选择QT GUI Application 会自动生成三个文件 "main.cpp" 、“qtappliction.h”和”qtappliction.cpp”

以及ui文件  "QtGuiApplication1.ui" 和 ui头文件 "ui_QtGuiApplication.h"

用Qt_Designer打开ui文件可以发现里面已经包含了一个名为centralWidget的Widget对象。

而我们需要在“qtappliction.h”和”qtappliction.cpp”中添加我们需要的组件：QLabel和QPushButton以及QLineEdit

/*------------------------qtapplication.h-----------------------*/
#include "ui_QtGuiApplication.h"
#include 
#include 
#include 
#include 

/*宏定义*/
///
#define pi 3.1415926

class QtGuiApplication1 : public QMainWindow
{
	Q_OBJECT

public:
	QtGuiApplication1(QWidget *parent = Q_NULLPTR);
	void InitConnect();

private:
	QLabel *m_pLabel1, *m_pLabel2;
	QLineEdit *m_pLineEdit1;
	QPushButton * m_pPushbotton1;
	bool m_bStartupIsOver;

private slots:         //槽函数必须要注明，不然无法建立信号槽
	void CalcArea();

private:
	Ui::QtGuiApplication1Class ui;
};

/*----------------------------qtapplication.cpp-------------------*/

#include "qtapplication.h"

QtGuiApplication1::QtGuiApplication1(QWidget *parent)
	: QMainWindow(parent)
{
	ui.setupUi(this);   //将ui跟我们的QtGuiApplication1对象关联


	m_pLabel1 = new QLabel(this);
	m_pLabel2 = new QLabel(this);
	m_pLabel1->setText(tr("please write the radis"));
	
	m_pLineEdit1 = new QLineEdit(this);
	m_pPushbotton1 = new QPushButton(this);
	m_pPushbotton1->setText(tr("build the area"));
	QGridLayout *m_pGridLayout = new QGridLayout(this);
	m_pGridLayout->addWidget(m_pLabel1, 0, 0);
	m_pGridLayout->addWidget(m_pLabel2, 0, 1);
	m_pGridLayout->addWidget(m_pLineEdit1, 1, 0);
	m_pGridLayout->addWidget(m_pPushbotton1, 1, 1);
	ui.centralWidget->setLayout(m_pGridLayout);   //这里要注意必须将我们的控件加到ui的centralWidget，不然MainWindow是无法显示控件的
	InitConnect();                    //初始化信号槽配置
	
}

void QtGuiApplication1::InitConnect()
{
	connect(m_pPushbotton1, SIGNAL(clicked()), this, SLOT(CalcArea())); //将按键的点击信号和面积计算函数建立信号槽
}

void QtGuiApplication1::CalcArea()
{
	QString valueStr= m_pLineEdit1->text();
	int valueInt = valueStr.toInt();
	double area = valueInt*valueInt*pi;
	QString tmpstr;
	m_pLabel2->setText(tmpstr.setNum(area));
}

#include "QtGuiApplication1.h"
#include 


int main(int argc, char *argv[])
{
	QApplication app(argc, argv); //创建qt应用
	QtGuiApplication1 w;   //创建窗口对象
	w.show();              //显示窗口对象
	return app.exec();     //执行应用消息循环
}

这是编译之后的运行结果：输入半径并点击按键会输出圆的面积