Child widget not updating parent widget layout

[jj382]

How can I force parent widgets to update their layout when a child layout changes its size hints? I have sizeHints overriden, and i call updateGeometry(), but none of these work. The layout updates only after a resizeEvent is called (which calls my updateLayout() function). Below is a full test case showing 3 layouts stacked on top of each other, and pressing button adds 50 pixels to teh top widget's height. (this is a test case, and i'm aware of existing QLayouts).

 #ifndef WIDGET_H_
 #define WIDGET_H_
 
 #include <QWidget>
 #include <QColor>
 #include <QPalette>
 #include <QPushButton>
 
 class SubWidget : public QWidget
 {
   Q_OBJECT
 public:
   SubWidget(QColor const& c, QWidget *parent = nullptr)
     : QWidget(parent), addedHeight_(0)
   {
     QPalette pal(palette());
     pal.setColor(QPalette::Background, c);
     setAutoFillBackground(true);
     setPalette(pal);
   }
 
   virtual QSize sizeHint() const override
   {
     return QSize(100, 50+addedHeight_);
   }
 
   virtual QSize minimumSizeHint() const override
   {
     return sizeHint();
   }
 
 public slots:
   void addFiftyPixelsToHeight()
   {
     addedHeight_ += 50; 
     updateGeometry();
     update();
   }
   
 private:
   int addedHeight_;
 };
 
 
 class MainWidget : public QWidget
 {
   Q_OBJECT
 public:
   explicit MainWidget(QWidget *parent = nullptr)
     : QWidget(parent)
   {
     topWidget_ = new SubWidget(QColor(Qt::red), this);
     botWidget_ = new SubWidget( QColor(Qt::yellow), this);
     button_    = new QPushButton(this);
 
     connect(button_, SIGNAL(clicked()), topWidget_, SLOT(addFiftyPixelsToHeight()));
     resize(200,300);
   }
 
   virtual void showEvent(QShowEvent *event) override
   {
     QWidget::showEvent(event);
   }
 
   virtual void resizeEvent(QResizeEvent *event) override
   {
     updateLayout();
     QWidget::resizeEvent(event);
   }
 
 private:
 
   // Update the layout of the widgets by stacking them on top of each other
   void updateLayout()
   {
     QRect const r = geometry();
 
     QSize const topSize    = topWidget_->sizeHint();
     QSize const bottomSize = botWidget_->sizeHint();
 
     QRect const topRect    = QRect(0,0, r.width(), topSize.height());
     QRect const bottomRect = QRect(0,topSize.height(), r.width(), bottomSize.height());
     QRect const buttonRect = QRect(0,topSize.height()+bottomSize.height(), 
                                    r.width(), r.height()-topSize.height()-bottomSize.height());
     topWidget_->setGeometry(topRect);
     botWidget_->setGeometry(bottomRect);
     button_->setGeometry(buttonRect);
   }
 
 
   SubWidget *topWidget_;
   SubWidget *botWidget_;
   QPushButton *button_;
 };
 
 
 
 
 #endif /* WIDGET_H_ */
 
 
 int main(int argc, char *argv[])
 {
   QApplication app(argc, argv);
 
   MainWidget w;
   w.show();
   
   return app.exec();
 }

[mrjj]

Hi and welcome
Have you tried with
QSizePolicy::Expanding
void QSizePolicy::setHorizontalPolicy(Policy policy)

so its set to use as much as possible.

[jj382]

@mrjj Yes. For this test case, I believe it would be setSizePolicy(QSizePolicy::MinimumExpanding, QSizePolicy::Expanding), but it does not work.