Qt findChild returning 0

Question

I'm currently working on a nice way to use a GUI to modify object contents at run time, project uses Qt. So I thought of passing a `QLayout` to the objects, to let them create their own GUI. As POC, I created this ("display" is the name of the `QVBoxLayout*` parameter): ``` QPushButton* button = new QPushButton(); button->setText("foo"); button->setObjectName("bar"); display->addWidget(button); ``` which works just as fine as expected. But I will need to read what the user typed into the GuI, so this is what I did next: ``` QPushButton *button2 = display->findChild(); if(button2) std::cout << button2->objectName().toStdString() << std::endl; ``` here nothing is put out - if() statement is false! ``` QList widgets = display->findChildren(); foreach (QWidget* b, widgets) { std::cout << b->objectName().toStdString() << std::endl; } ``` similarly, the `widgets` list is empty. I tried looking through the full member list at: http://doc.qt.digia.com/qt/q…

Accepted Answer

The parent of a `QWidget` must be a `QWidget`. `QLayout` is not a `QWidget`.

Layouts exist to move and resize the children of a `QWidget`. Though you may add child widgets by making calls on the layout, ultimately, their parent will be the `QWidget` that the layout resides on.

To illustrate:

```
QWidget* widget = new QWidget;
qDebug("Widget: %p", widget);

QHBoxLayout* layout = new QHBoxLayout;
qDebug("Layout: %p", layout);

QWidget* child = new QWidget;
layout->addWidget(child);

qDebug("Child's parent before setLayout: %p", child->parent());
widget->setLayout(layout);
qDebug("Child's parent after setLayout: %p", child->parent());
```

Output:

```
Widget: 0x8e1c1e0
Layout: 0x8e1c3f0
Child's parent before setLayout: 0x0
Child's parent after setLayout: 0x8e1c1e0
```

Qt findChild returning 0

Solution

Problem