How to find a widget through QApplication::instance()?

[MT339M]

Main_window::Main_window (QWidget *parent) : QMainWindow(parent) {
    QHBoxLayout *layout = new QHBoxLayout;
    QPushButton *button = new QPushButton("button");
    QPushButton *button2 = new QPushButton("button2");

    button->connect(button, &QPushButton::clicked, this, &Main_window::do_something);
    button2->setObjectName("button2");

    layout->addWidget(button);
    layout->addWidget(button2);

    this->UI.setupUi(this);
    this->centralWidget()->setLayout(layout);
}
void Main_window::do_something ()  {
    QPushButton *button2 = QApplication::instance()->findChild<QPushButton *>("button2");
    
    qDebug() << button2; // QWidget(0x0)
}

I want to find a widget using findChild() method with QApplication::instance(), but it's not working.

QApplication::instance()->findChild<QPushButton *>("button2");

When I use findChild() method with Main_window's instance, it works well.

this->findChild<QPushButton *>("button2");

Could you tell me why it fails with QApplication::instance(), and how to solve this? Thanks in advance.

[Christian Ehrlicher]

I don't know exactly why it does not work but also don't understand why you would need it.

[MT339M]

@Christian-Ehrlicher
I want to access a widget from afar without pass widget as argument.

void Main_window::do_something ()  {
    for (auto &widget : QApplication::allWidgets())
        if (widget->objectName() == "button2") {
            QPushButton *button2 = static_cast<QPushButton *>(widget);
            
            qDebug() << button2;
        }
}

The above solution is working well. It's weird..

[Christian Ehrlicher]

Looks like no good design.
Please provide a minimal, compileable testcase.

[Bonnie]

Not a good design +1.
However, about the question, it's simple, because a widget (or any other QObject) is normally not QApplication::instance()'s child, unless you have set the parent to be it.
You could use QApplication::allWidgets() or QApplication::topLevelWidgets() to iterate widgets of the application, but still not a good design.

[MT339M]

@Bonnie
Thanks for your answer!