Why doesnt the old widget get removed? - c++

Question

Because of the mouseEvent, I would expect the red and blue widgets to switch places on every click. Instead the red switches to the blue and then it never switches back, why?
Frame *red = NULL;
Frame *blue = NULL;
bool isRed = true;
Frame::Frame(QWidget *parent) :
QFrame(parent)
{
}
Frame::~Frame(){
printf("deleted.\n");
fflush(0);
}
void QLayout_clear(QLayout* layout, bool deleteWidgets){
QLayoutItem* item;
QLayout* childLayout;
while ((item = layout->takeAt(0)) != NULL){
QWidget* widget = item->widget();
if (widget != NULL){
layout->removeWidget(widget);
if (deleteWidgets){
delete widget;
}
} else if (childLayout = item->layout()){
QLayout_clear(childLayout, deleteWidgets);
}
//delete item;
}
}
Widget::Widget(QWidget *parent)
: QWidget(parent)
{
QVBoxLayout *layout = new QVBoxLayout;
this->setLayout(layout);
red = new Frame;
red->setFixedSize(100,100);
red->setStyleSheet("background-color:red");
blue = new Frame;
blue->setFixedSize(100,100);
blue->setStyleSheet("background-color:blue");
layout->addWidget(red);
}
void Widget::mouseReleaseEvent(QMouseEvent *){
printf("clicked.\n");
fflush(0);
QVBoxLayout *layout = (QVBoxLayout *)this->layout();
if (1){ //it doesnt matter if this is 1 or 0
delete layout;
layout = new QVBoxLayout;
this->setLayout(layout);
} else {
QLayout_clear(layout, false);
}
if (isRed){
layout->addWidget(blue);
isRed = false;
} else {
layout->addWidget(red);
isRed = true;
}
}
Note: here I am using a simple QFrame for the widgets to switch, in my application the widgets are much more complicated and I cannot recreate them every time I want to swap.

Answer 1

I believe it is not good practice from performance point of view to delete and recreate layers each time you want to switch frames, it would be easier to add both frames to the layer and then set visible only frame you want to appear. Also, boolean isRed is not necessary as info about visibility is contained within each frame itself...
Try this:
QFrame *red = NULL;
QFrame *blue = NULL;
Widget::Widget(QWidget *parent)
: QWidget(parent)
{
QVBoxLayout *layout = new QVBoxLayout(this);
red = new QFrame(this);
red->setFixedSize(100,100);
red->setStyleSheet("background-color:red");
red->setHidden(false);
blue = new QFrame(this);
blue->setFixedSize(100,100);
blue->setStyleSheet("background-color:blue");
blue->setHidden(true);
layout->addWidget(red);
layout->addWidget(blue);
this->setLayout(layout);
}
void Widget::mouseReleaseEvent(QMouseEvent *){
printf("clicked.\n");
fflush(0);
red->setHidden(!red->isHidden());
blue->setHidden(!blue->isHidden());
}

Answer 2

The layout destructs its children. Because addWidget takes ownership so delete layout will delete red and blue widgets too.