Can't add an object derived from QWidget in a layout.

[Netich]

Hi, i have one widget defined lik this:

class TestWidget: public QWidget, private Ui::TestWidget

class TestWidget: public QWidget, private Ui::TestWidget

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I thougt that is it is derived from QWidget, can be added in a layout using ->addWidget().

Is this wrong? How can I put it in the MainWindow?

Thanks

[Netich]

If i use a cast to QWidget i can insert it, but why i can addWidget(QSpinBox) and cannot addWidget(QSpinBox) ??