How to properly delete items from the QWidget - qt

Question

This is the code for populating and deleting item from the QWidget.
class ShowCommands : public QWidget
{
private:
QWidget wdg;
QVBoxLayout m_layout;
QScrollArea* m_area;
QWidget m_contents;
QVBoxLayout m_contentsLayout;
bool isWrite;
public:
ShowCommands(QWidget *parent = nullptr);
void showWindow();
void setParent(QWidget* par);
void AddCommand(std::string stdstrCommand);
};
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
ShowCommands::ShowCommands(QWidget *parent) : QWidget(parent)
{
isWrite = true;
m_area = new QScrollArea;
m_contents.setLayout(&m_contentsLayout);
m_layout.addWidget(m_area);
m_area->setWidget(&m_contents);
m_contentsLayout.setSizeConstraint(QLayout::SetMinimumSize);
wdg.setLayout(&m_layout);
wdg.setFixedWidth(650);
wdg.setWindowTitle("Commands");
wdg.setWindowFlags(Qt::Window
| Qt::FramelessWindowHint);
wdg.hide();
}
///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
void ShowCommands::showWindow()
{
if (isWrite == false)
{
if (m_contentsLayout.layout() != NULL)
{
QLayoutItem* item;
while ((item = m_contentsLayout.layout()->takeAt(0)) != NULL)
{
delete item->widget();
delete item;
}
}
isWrite = true;
wdg.show();
// AddCommand() function is called now multiple times and items are populated.
}
else
{
isWrite = false;
wdg.hide();
}
}
void ShowCommands::AddCommand(std::string stdstrCommand)
{
if (isWrite)
{
QLabel *label = new QLabel;
label->setText(stdstrCommand.c_str());
m_contentsLayout.addWidget(label);
}
}
In the showWindow() function first all of the items of widget are deleted and than populate the widget with new items.
The issue is that after i delete the existing items the new items are not populated from top to bottom but they start appearing from center.

Answer 1

I see many problems with your code, some of them make it hard to read, but anyway I think the main problem here is how properly create those items ...
You should create your widgets as pointers and assign good parenting to them, unparented widgets will create a new window. You should do something like this.
class MyWidget: public QWidget
{
Q_OBJECT
public;
MyWidget(QWidget *parent=nullptr) : QWidget(parent)
{
w1=new QWidget(this);
}
private:
class QWidget *m_w1;
}
that way you will have a child widget that will be drawn relative to you in the same window. You can add a layout to your widget, and then add your widgets to it so it handles the location for you. ie:
class MyWidget: public QWidget
{
Q_OBJECT
public;
MyWidget(QWidget *parent=nullptr) : QWidget(parent)
{
//passing this to the construct assign layout to 'this' widget
QVBoxLayout *verticalLayout=new QVBoxLayout(this);
w1=new QWidget(this);
w2=new QWidget(this);
verticalLayout->addWidget(w1);
verticalLayout->addWidget(w2);
}
private:
class QWidget *m_w1;
class QWidget *m_w2;
}
in that case both widgets will be display one below the other in the space assigned to you. Also the space assigned to you will depend on the characteristics of the two child widgets (you probably will create something derived from QWidget).
Now about the QScrollArea, that widget it is meant to be used with a widget placed 'inside', and you should add items to the layout of that one. ie:
class MyWidget: public QWidget
{
Q_OBJECT
public;
MyWidget(QWidget *parent=nullptr) : QWidget(parent)
{
//passing this to the construct assign layout to 'this' widget
QVBoxLayout *verticalLayout=new QVBoxLayout(this);
m_scroll=new QScrollArea(this);
verticalLayout->addWidget(m_scroll);
m_containerwidget=new QWidget(this);
//this sets our container widget as the inside's scrollarea widget
m_scroll->setWidget(m_containerwidget);
//if your widget will resize along the way you use this, in your case you do
m_scroll->setWidgetResizable(true);
m_containerLayout=new QVBoxLayout (m_containerwidget);
m_w1=new QWidget(this);
m_w2=new QWidget(this);
m_containerLayout->addWidget(m_w1);
m_containerLayout->addWidget(m_w2);
}
private:
class QScrollArea *m_scroll;
class QWidget *m_containerwidget;
class QVBoxLayout *m_containerLayout;
class QWidget *m_w1,m_w2;
}
You don't usually store all that information (m_containerLaoyut,m_containerWidget) in the class as you can query the objects for them, but just for clarity I add them there.
The last example applies to your scenario, you could store your 'items widgets' in a list, or query the layout for them, and when you need to delete them you just do that and then add new ones to the layout.
Of course you can use any kind of layout, I used vertical just as an example.