请问一个QT标准INT输入框的小疑点

请教一个QT标准INT输入框的小问题
看书上的例子通过点击主界面的按钮弹出标准INT输入对话框，可是总是有异常自动退出，不知道为什么呢，麻烦大家帮帮忙 ，感激不尽了
上代码来：
dialog.h
#ifndef DIALOG_H
#define DIALOG_H

#include <QtGui/QDialog>
#include "inputdlg.h"
#include <QGridLayout>
class Dialog : public QDialog
{
  Q_OBJECT

public:
  Dialog(QWidget *parent = 0);
  
private:
  QPushButton *inputBtn;
  InputDlg *inDlg;
  QGridLayout *mainlayout;
private slots:
  void showInputDlg();
};

#endif // DIALOG_H




//dialog.cpp
#include "dialog.h"
#include <QGridLayout>
#include <QPushButton>

Dialog::Dialog(QWidget *parent)
  : QDialog(parent)
{
  inputBtn =new QPushButton;
  inputBtn->setText(tr("awrwarfwaf"));
  mainlayout->addWidget(inputBtn,2,0);
  connect(inputBtn,SIGNAL(clicked()),this,SLOT(showInputDlg()));



}


void Dialog::showInputDlg()
{
  inDlg=new InputDlg(this);
  inDlg->show();
}


//inputdlg.h
#ifndef INPUTDLG_H
#define INPUTDLG_H

#include <QDialog>
#include <QLabel>
#include <QPushButton>
#include <QGridLayout>

class InputDlg : public QDialog
{
  Q_OBJECT

public:
  InputDlg(QWidget *parent = 0);

private slots:
  void change();

private:
  QLabel *time1;
  QLabel *time2;
  QPushButton *sztime;
  QGridLayout *mainLayout;
};

#endif // INPUTDLG_H



//inputdlg.cpp
#include "inputdlg.h"
#include <QInputDialog>

InputDlg::InputDlg(QWidget *parent) :
  QDialog(parent)
{

  //setWindowTitle(tr("程序设置"));

  time1=new QLabel;
  time1->setText(tr("设置时间"));
  time2=new QLabel;
  time2->setText(tr("1"));
  time2->setFrameStyle(QFrame::Panel|QFrame::Sunken);

  sztime=new QPushButton;
  sztime->setText(tr("设置"));

  mainLayout->addWidget(time1,0,0);
  mainLayout->addWidget(time2,0,1);
  mainLayout->addWidget(sztime,0,2);

  connect(sztime,SIGNAL(clicked()),this,SLOT(change()));
}
void InputDlg::change()
{
  bool ok;
  int t = QInputDialog::getInt(this,tr("设置自动播放时间"),tr("请输入时间："),time2->text().toInt(&ok),0,100,1,&ok);
  if (ok)
  time2->setText(QString(tr("%1")).arg(t));
}

//main.cpp
#include <QtGui/QApplication>
#include "dialog.h"
#include <QTextCodec>
int main(int argc, char *argv[])
{
  QApplication a(argc, argv);
  QTextCodec::setCodecForTr(QTextCodec::codecForLocale());
  Dialog w;
  w.show();

  return a.exec();
}






谢谢 ，谢谢大家咯，感激不尽

------解决方案--------------------
sztime->setText(tr("设置"));

mainLayout->addWidget(time1,0,0);
mainLayout->addWidget(time2,0,1);
mainLayout->addWidget(sztime,0,2);

仔细看，mainLayout同有new就使用了
------解决方案--------------------
在InputDlg的构造函数里面加上这句mainLayout=new QGridLayout;