Why am I unable to delete tabWidget in Qt Designer? - c++

Question

I am using Qt Designer in combination with MSVC2019. I recently changed my form's base class from QWidget to QMainWindow manually by editing the .ui file, header, and constructor. In this form I have a tabWidget, which is now not able to be selected. It shows up in the object inspector and property editor, and I can edit its properties, but not select it. This is unlike all the other widgets in my form. When I right-click on the tabWidget in the Object inspector it gives the same menu options as a QMainWindow (Create Menu Bar, Add Tool Bar).
I have tried changing various object properties of the tabWidget and its main window but nothing has worked.
Here is the .ui region of interest. All I did was replace Widget with QMainWindow in line 4.
<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
<class>campanel</class>
<widget class="QMainWindow" name="campanel">
<property name="enabled">
<bool>true</bool>
</property>
<property name="geometry">
<rect>
<x>0</x>
<y>0</y>
<width>1509</width>
<height>984</height>
</rect>
</property>
<property name="sizePolicy">
<sizepolicy hsizetype="Fixed" vsizetype="Fixed">
<horstretch>0</horstretch>
<verstretch>0</verstretch>
</sizepolicy>
</property>
<property name="windowTitle">
<string>FASTPLOTTER</string>
</property>
<property name="windowIcon">
<iconset>
<normaloff>bigmoves.ico</normaloff>bigmoves.ico</iconset>
</property>
<property name="windowOpacity">
<double>1.000000000000000</double>
</property>
<property name="autoFillBackground">
<bool>false</bool>
</property>
<property name="styleSheet">
<string notr="true">background-color: rgb(255, 255, 255);</string>
</property>
<property name="tabShape">
<enum>QTabWidget::Rounded</enum>
</property>
<property name="dockNestingEnabled">
<bool>true</bool>
</property>
<property name="dockOptions">
<set>QMainWindow::AllowNestedDocks|QMainWindow::AllowTabbedDocks|QMainWindow::AnimatedDocks|QMainWindow::ForceTabbedDocks</set>
</property>
<widget class="QTabWidget" name="tabWidget">
<property name="enabled">
<bool>true</bool>
</property>
<property name="sizePolicy">
<sizepolicy hsizetype="Expanding" vsizetype="Expanding">
<horstretch>0</horstretch>
<verstretch>0</verstretch>
</sizepolicy>
</property>
<property name="tabPosition">
<enum>QTabWidget::West</enum>
</property>
<property name="currentIndex">
<number>1</number>
</property>
<property name="documentMode">
<bool>true</bool>
</property>
<property name="tabsClosable">
<bool>true</bool>
</property>
<property name="movable">
<bool>true</bool>
</property>
<widget class="QWidget" name="iolji">
<attribute name="title">
<string/>
</attribute>
</widget>
<widget class="QWidget" name="tab">
<attribute name="title">
<string/>
</attribute>
</widget>
</widget>

Answer 1

QMainWindow is a special case of QWidget: it has a menu bar, a status bar, tool bars, can add dockable frames, and have a central-widget. While you can switch between QWidget and QDialog in UI files, when switching to QMainWindow you must embed all the content of previous widget into the centralWidget:
<widget class="QMainWindow" name="MainWindow">
<!-- size policy, geometry... -->
<widget class="QWidget" name="centralwidget">
<!-- size policy, layout, content of your previous QWidget -->
</widget>
</widget>