inherited QPushButton is not being displayed in a layout

[seux]

Hello,
I want to create a new QPushButton, so I inherited it like this:

class MyButton : public QPushButton
{
    Q_OBJECT
public:
    MyButton(const QString &text, QWidget *parent = 0);
 
    QPushButton *btn;
};

class MyButton : public QPushButton
{
    Q_OBJECT
public:
    MyButton(const QString &text, QWidget *parent = 0);

    QPushButton *btn;
};

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the code of the constructor looks like this:

MyButton::MyButton(const QString &text, QWidget *parent)
{
    btn = new QPushButton(text);
    btn->setFlat(true);
    //btn->show();
    btn->setMaximumHeight(30);
}

MyButton::MyButton(const QString &text, QWidget *parent)
{
    btn = new QPushButton(text);
    btn->setFlat(true);
    //btn->show();
    btn->setMaximumHeight(30);
}

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When I now add a new MyButton to my MainWindow widget it does not show up, but when I remove the two slashes before btn->show(), the new button is drawn in a separate window. Why does the button only appear in a separate window and not in my main widget?

Here is the code snipped from the main widget:

Btn1 = new MyButton("Hello World");
layout->addWidget(Btn1);

Btn1 = new MyButton("Hello World");
layout->addWidget(Btn1);

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