QWidget application does not display anything

[PstdEr]

I have written the following program using QWidget

and placed some pushbuttons and labels in layout and added those in another layout, but nothing is getting displayed except some default window.

Must i have QMainwindow always as a base widget?

please help.

apphub.cpp
----------------

#include "apphub.h"
#include<QDebug>
 
 
AppHub::AppHub(QWidget *parent) : QWidget(parent)
{
    qDebug() << "AppHub";
 
    Mainwidget = new QWidget;
    MainLayout = new QGridLayout;
    Mainwidget->setLayout(MainLayout);
 
 
    //Mainwidget->setPalette(QPalette(QColor(255,0,0,255)));
    //Mainwidget->setAutoFillBackground(true);
    Mainwidget->setMinimumSize(500,500);
 
    for(int r=0;r<1;r++) {
        for(int c=0;c<2;c++) {
            App = new AppRsrc;
            MainLayout->addWidget(App,r,c,10,2,Qt::AlignTop);
        }
    }
    //Mainwidget->show(); 
   // showing the window seperately , but  without this also it should show
}
 
AppHub::~AppHub()
{
 
}
 
AppRsrc:: AppRsrc()
{
    qDebug() << "AppRsrc";
    AppWidget = new QWidget ;
    AppButton = new QPushButton;
    AppLayout = new QVBoxLayout;
    AppNameLbl = new QLabel;
    AppWidget->resize(98,97);
    AppWidget->setPalette(QColor(255,0,0,255));
    AppWidget->setAutoFillBackground(true);
    QPixmap pixmap(":/appimages/orca.png");
    QIcon AppIcon(pixmap);
    AppButton->setFixedSize(100,100);
    AppButton->setIcon(AppIcon);
    AppNameLbl->setFixedSize(83,20);
 
    AppLayout->addWidget(AppButton);
    AppLayout->addWidget(AppNameLbl);
 
    AppWidget->setLayout(AppLayout);
}
 
AppRsrc:: ~AppRsrc()
{
 
}

#include "apphub.h"
#include<QDebug>


AppHub::AppHub(QWidget *parent) : QWidget(parent)
{
    qDebug() << "AppHub";

    Mainwidget = new QWidget;
    MainLayout = new QGridLayout;
    Mainwidget->setLayout(MainLayout);


    //Mainwidget->setPalette(QPalette(QColor(255,0,0,255)));
    //Mainwidget->setAutoFillBackground(true);
    Mainwidget->setMinimumSize(500,500);

    for(int r=0;r<1;r++) {
        for(int c=0;c<2;c++) {
            App = new AppRsrc;
            MainLayout->addWidget(App,r,c,10,2,Qt::AlignTop);
        }
    }
    //Mainwidget->show(); 
   // showing the window seperately , but  without this also it should show
}

AppHub::~AppHub()
{
    
}

AppRsrc:: AppRsrc()
{
    qDebug() << "AppRsrc";
    AppWidget = new QWidget ;
    AppButton = new QPushButton;
    AppLayout = new QVBoxLayout;
    AppNameLbl = new QLabel;
    AppWidget->resize(98,97);
    AppWidget->setPalette(QColor(255,0,0,255));
    AppWidget->setAutoFillBackground(true);
    QPixmap pixmap(":/appimages/orca.png");
    QIcon AppIcon(pixmap);
    AppButton->setFixedSize(100,100);
    AppButton->setIcon(AppIcon);
    AppNameLbl->setFixedSize(83,20);

    AppLayout->addWidget(AppButton);
    AppLayout->addWidget(AppNameLbl);

    AppWidget->setLayout(AppLayout);
}

AppRsrc:: ~AppRsrc()
{

}

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apphub.h
----------------

#ifndef APPHUB_H
#define APPHUB_H
 
#include <QWidget>
#include <QPushButton>
#include <QGridLayout>
#include <QLabel>
#include "app_rsrc.h"
 
class AppRsrc;
class AppHub : public QWidget
{
    Q_OBJECT
 
public:
    AppHub(QWidget *parent = 0);
    ~AppHub();
 
private:
    QWidget *Mainwidget;
    AppRsrc *App;
    QGridLayout *MainLayout;
 
};
 
#endif // APPHUB_H

#ifndef APPHUB_H
#define APPHUB_H

#include <QWidget>
#include <QPushButton>
#include <QGridLayout>
#include <QLabel>
#include "app_rsrc.h"

class AppRsrc;
class AppHub : public QWidget
{
    Q_OBJECT
    
public:
    AppHub(QWidget *parent = 0);
    ~AppHub();

private:
    QWidget *Mainwidget;
    AppRsrc *App;
    QGridLayout *MainLayout;

};

#endif // APPHUB_H

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app_rsrc.h
----------------
 
#ifndef APP_RSRC_H
#define APP_RSRC_H
 
#include<QPushButton>
#include<QLabel>
#include<QGridLayout>
#include<QIcon>
#include<QWidget>
 
class AppRsrc : public QWidget
{
private:
    QWidget *AppWidget;
    QPushButton *AppButton;
    QVBoxLayout *AppLayout;
    QLabel *AppNameLbl;
 
public:
    AppRsrc();
    ~AppRsrc();
};
 
#endif // APP_RSRC_H

app_rsrc.h
----------------

#ifndef APP_RSRC_H
#define APP_RSRC_H

#include<QPushButton>
#include<QLabel>
#include<QGridLayout>
#include<QIcon>
#include<QWidget>

class AppRsrc : public QWidget
{
private:
    QWidget *AppWidget;
    QPushButton *AppButton;
    QVBoxLayout *AppLayout;
    QLabel *AppNameLbl;

public:
    AppRsrc();
    ~AppRsrc();
};

#endif // APP_RSRC_H

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main.cpp
----------------

#include "apphub.h"
#include <QApplication>
#include<QMainWindow>
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    AppHub w;
 
    w.show();
 
    return a.exec();
}

#include "apphub.h"
#include <QApplication>
#include<QMainWindow>
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    AppHub w;

    w.show();
    
    return a.exec();
}

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