Problem with my own widget

[Macok]

Hello,
Im new to Qt, today i created very simple widget:

class MyWidget : public QWidget{
public:
    MyWidget(QWidget *parent=0);
};
 
MyWidget::MyWidget(QWidget *parent)
        :QWidget(parent)
{
    setFixedSize(200, 100);
    QPushButton *button=new QPushButton(tr("Przycisk"), this);
    button->setGeometry(20, 30, 100, 50);
}

class MyWidget : public QWidget{
public:
    MyWidget(QWidget *parent=0);
};

MyWidget::MyWidget(QWidget *parent)
        :QWidget(parent)
{
    setFixedSize(200, 100);
    QPushButton *button=new QPushButton(tr("Przycisk"), this);
    button->setGeometry(20, 30, 100, 50);
}

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As you can see, this widget is only window and button placed in it.

I added 2 lines (10 and 11) to main.cpp to display this widget:

#include <QtGui/QApplication>
#include "mainwindow.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
 
    MyWidget widget; 
    widget.show();
 
    return a.exec();
}

#include <QtGui/QApplication>
#include "mainwindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    MyWidget widget; 
    widget.show();

    return a.exec();
}

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It works fine, but now I'd like to display MyWidget when user click on button placed on MainWindow.
I created "buttonDown()" slot and connected it with pushButton from MainWindow:

void MainWindow::buttonDown(){
    MyWidget widget();
    widget.show();
}

void MainWindow::buttonDown(){
    MyWidget widget();
    widget.show();
}

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But when I click on button nothing happens
So displaying this widget from main function works fine, but displaying it from another function in exactly the same way doesn't.
What should i do?

PS. The whole code have been generated by Qt Creator.
I have only added MyWidget class, and buttonDown slot.
Sorry for bad english.


@EDIT
I solved problem, but I still need help.
I replaced those lines:

MyWidget widget;
    widget.show();

MyWidget widget;
    widget.show();

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By these:

MyWidget widget=new MyWidget;
    widget->show();

MyWidget widget=new MyWidget;
    widget->show();

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And it works now, but what is bad in first method?
I thought it doesn't make any difference.

[rexi]

MyWidget widget;
    widget.show();

MyWidget widget;
    widget.show();

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Here you create the widget on the stack. When the method exits, widget gets out of scope and is destroyed immediately, hence you don't see anything.

MyWidget widget=new MyWidget;
    widget->show();

MyWidget widget=new MyWidget;
    widget->show();

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This creates widget on the heap, which means it won't be destroyed when the method exits.

I suggest you read up on C++ and scopes.