How to dynamically swap QWidgets - c++

Question

I have a QMainWindow which contains, on the left, a QTreeWidget and, on the right, another QMainWindow with windowFlags set to Qt::Widget.
This is because the QMainWindow is the only way to provide docking functionality to a QWidget. (I want the docked components to be popped out of the "real" window entirely if needed.
My problem is that I want users to be able to keep popped out dock widgets even if their item is not selected on the left.
For example, here is the global layout:
Let's say I select Item 1. On the right I will have some dockable widgets which I am able to reorder as I wish. If I pop one out to keep an eye on it, I don't want it to disappear if I select Item 2.
To go even further, I could want to show ALL Items' dockable widgets at once if I want.
My original idea to achieve this was to make each Item have its dedicated QMainWindow stored inside its data and I would just switch the right one to reflect the currently active one.
Maybe what I want is a bad idea and maybe it's not even feasible.
Could someone with some Qt knowledge tell me if I'm doing/wanting something wrong please?
Edit:
It would be perfectly fine to me if there were a way to trigger the "inner QMainWindow" pop out manually. Like, for example, a button "pop out" in the top right corner which would completely pop it and make it an entirely new window (still linked to the other one, though)
Edit2:
I's like to point out that I haven't tried anything regarding this question yet. I am essentially wondering if it fits with Qt's way of doing things.
This question made me happy about being able to provide docking capabilities to only a part of the program but I still aren't sure about what I want. Can I really achieve this?
Edit7, MVCE:
Hopefully I didn't forget anything since this is done by modifying my files.
mainwindow2.cpp
#include "mainwindow2.hh"
#include "ui_mainwindow2.h"
#include <QTreeWidgetItem>
MainWindow2::MainWindow2(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow2)
{
ui->setupUi(this);
ui->mainPanel->setWindowFlags(Qt::Widget);
QTreeWidgetItem* item = new QTreeWidgetItem;
item->setData(0, 0, QVariant::fromValue(QString("Item 1")));
ui->accountsTreeWidget->addTopLevelItem(item);
QTreeWidgetItem* item2 = new QTreeWidgetItem;
item2->setData(0, 0, QVariant::fromValue(QString("Item 2")));
ui->accountsTreeWidget->addTopLevelItem(item2);
}
MainWindow2::~MainWindow2()
{
delete ui;
}
mainwindow2.hh
#ifndef MAINWINDOW2_HH
#define MAINWINDOW2_HH
#include <QMainWindow>
namespace Ui {
class MainWindow2;
}
class MainWindow2 : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow2(QWidget *parent = 0);
~MainWindow2();
private:
Ui::MainWindow2 *ui;
};
#endif // MAINWINDOW2_HH
mainwindow2.ui
<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>MainWindow2</class>
<widget class="QMainWindow" name="MainWindow2">
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>1200</width>
<height>700</height>
</rect>
</property>
<property name="minimumSize">
<size>
<width>1200</width>
<height>700</height>
</size>
</property>
<property name="windowTitle">
<string>Main Window</string>
</property>
<widget class="QWidget" name="centralWidget">
<property name="minimumSize">
<size>
<width>1200</width>
<height>658</height>
</size>
</property>
<layout class="QGridLayout" name="gridLayout">
<item row="0" column="1" rowspan="2" colspan="2">
<widget class="QMainWindow" name="mainPanel"/>
</item>
<item row="0" column="0">
<widget class="QTreeWidget" name="accountsTreeWidget">
<property name="minimumSize">
<size>
<width>200</width>
<height>0</height>
</size>
</property>
<property name="maximumSize">
<size>
<width>300</width>
<height>16777215</height>
</size>
</property>
<property name="frameShape">
<enum>QFrame::NoFrame</enum>
</property>
<property name="selectionBehavior">
<enum>QAbstractItemView::SelectItems</enum>
</property>
<property name="uniformRowHeights">
<bool>true</bool>
</property>
<attribute name="headerVisible">
<bool>false</bool>
</attribute>
<column>
<property name="text">
<string notr="true">1</string>
</property>
</column>
</widget>
</item>
</layout>
</widget>
</widget>
<layoutdefault spacing="6" margin="11"/>
<connections/>
</ui>
main.cpp
#include "mainwindow2.hh"
#include <QApplication>
#include <QStyleFactory>
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
app.setStyle(QStyleFactory::create("Fusion"));
MainWindow2 w;
w.show();
return app.exec();
}
project.pro
#-------------------------------------------------
#
# Project created by QtCreator 2017-11-12T23:07:49
#
#-------------------------------------------------
QT += core gui
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
TARGET = project
TEMPLATE = app
DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000 # disables all the APIs deprecated before Qt 6.0.0
INCLUDEPATH += $$PWD
SOURCES += \
main.cpp \
mainwindow2.cpp
HEADERS += \
mainwindow2.hh
FORMS += \
mainwindow2.ui

Answer 1

In the right side, you could add a parent widget, with a QBoxLayout, attach all the items to it, and just hide, show and sort them as you wish.
Make them a custom class, with a public int variable to let you identify them later on. Store their pointers in a QList, and then just loop the list and hide or show items by your criteria ( Using the int variable ).
Example:
Items form category A -> int value 0
Items form category B -> int value 1
etc...