QMainWindows show empty QWidget

[Tarko1976]

How do I remove max and min buttons in frmmantenimientosexo?

FrmMantenimientoSexo::FrmMantenimientoSexo(const QString strUserName, const QString strTableName, QWidget *parent) : QWidget(parent)
{
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.
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this->setWindowFlags(Qt::WindowMinimizeButtonHint | Qt::WindowMinimizeButtonHint);

FrmMantenimientoSexo::FrmMantenimientoSexo(const QString strUserName, const QString strTableName, QWidget *parent) : QWidget(parent)
{
.
.
.

this->setWindowFlags(Qt::WindowMinimizeButtonHint | Qt::WindowMinimizeButtonHint);

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that's not work.