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Qt_chapter01_02

+dialog.h
+
+#ifndef DIALOG_H
+#define DIALOG_H
+#include<QLabel>
+#include <QLineEdit>
+#include <QPushButton>
+#include <QDialog>
+
+class Dialog : public QDialog
+{
+    Q_OBJECT
+
+public:
+    Dialog(QWidget *parent = 0);
+    ~Dialog();
+private:
+    QLabel *label1,*label2;
+    QLineEdit *lineEdit;
+    QPushButton *button;
+private slots:
+    void showArea();
+
+};
+
+#endif // DIALOG_H
+
+==================================================================
+dialog.cpp
+
+#include "dialog.h"
+#include<QGridLayout>
+const static double PI=3.1416;
+
+
+Dialog::Dialog (QWidget *parent)
+    :QDialog (parent)
+{
+    label1=new QLabel(this) ;
+    label1->setText(tr ("请输入圆的半径: ")) ;
+    lineEdit=new QLineEdit (this) ;
+    label2=new QLabel(this) ;
+    button=new QPushButton (this) ;
+    button->setText (tr ("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(bool)),this,SLOT(showArea()));
+}
+
+Dialog::~Dialog()
+{
+
+}
+
+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));
+}