Scroll bars in scroll area not comming in scroll area

i created scroll area using designer and adding line edit in run time, when button clicked….
But scroll area is not expanding(scroll bars are inactive even though i set scrollbarAlways on)
please help me…
here is my complete code..
mainwindow.h
[CODE] #ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
Q_OBJECT

public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();

private slots:
void on_pushButton_clicked();

private:
Ui::MainWindow *ui;
};

#endif // MAINWINDOW_H[/CODE]

mainwindow.cpp

[CODE]
#include "mainwindow.h"
#include "ui_mainwindow.h"

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

}

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

void MainWindow::on_pushButton_clicked()
{
QLineEdit *le=new QLineEdit;

ui->gridLayout->addWidget(le);

ui->scrollArea->setWidgetResizable(true);

}
[/CODE]
mainwindow.ui
[CODE]
<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>MainWindow</class>
<widget class="QMainWindow" name="MainWindow">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>400</width>
<height>300</height>
</rect>
</property>
<property name="windowTitle">
<string>MainWindow</string>
</property>
<widget class="QWidget" name="centralWidget">
<layout class="QVBoxLayout" name="verticalLayout">
<property name="sizeConstraint">
<enum>QLayout::SetMinAndMaxSize</enum>
</property>
<item>
<widget class="QScrollArea" name="scrollArea">
<property name="widgetResizable">
<bool>true</bool>
</property>
<widget class="QWidget" name="scrollAreaWidgetContents">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>380</width>
<height>198</height>
</rect>
</property>
<widget class="QWidget" name="">
<property name="geometry">
<rect>
<x>40</x>
<y>31</y>
<width>216</width>
<height>25</height>
</rect>
</property>
<layout class="QGridLayout" name="gridLayout">
<property name="sizeConstraint">
<enum>QLayout::SetMinAndMaxSize</enum>
</property>
<item row="0" column="0">
<widget class="QPushButton" name="pushButton_2">
<property name="text">
<string>PushButton</string>
</property>
</widget>
</item>
<item row="0" column="1">
<widget class="QLineEdit" name="lineEdit"/>
</item>
</layout>
</widget>
</widget>
</widget>
</item>
<item>
<widget class="QPushButton" name="pushButton">
<property name="text">
<string>PushButton</string>
</property>
</widget>
</item>
</layout>
</widget>
<widget class="QMenuBar" name="menuBar">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>400</width>
<height>21</height>
</rect>
</property>
</widget>
<widget class="QToolBar" name="mainToolBar">
<attribute name="toolBarArea">
<enum>TopToolBarArea</enum>
</attribute>
<attribute name="toolBarBreak">
<bool>false</bool>
</attribute>
</widget>
<widget class="QStatusBar" name="statusBar"/>
</widget>
<layoutdefault spacing="6" margin="11"/>
<resources/>
<connections/>
</ui>
[/CODE]