How to catch clicks on blocked window?

Question

There are two windows in my Qt project: parant and child. Child window is modal, so all clicks on parent window are ignored by system. I need to react on mouse clicks on internal part of parant window (I understand that it is strange requirement, but I can't persuade customer to do not ask it).

So what do we have: parent window is disabled (because child window is opened and modal). And I need to catch mouse click on this blocked (disabled) window.

I see two ways to do it:

1. Simulate modality of child window. It is my current temporary solution: I've commented out line setWindowModality(Qt::WindowModal); in the code of child window (i.e. child window is not modal now), so I can catch mouse clicks on parent window. And I've set eventFilter() for parent window to ignore the most of actions. This solution works, but it looks wrong and rough.

2. Find way to catch mouse events on disabled window. Unfortunatelly I can't catch it by eventFilter() (because input of parent window is blocked). Do you see other approaches?

Or do you see other ways to do it?

Answer 1

This can be done by installing an event filter on the parent window inside the child window.

Here is an example project I did to demonstrate it:

untitled3.pro:

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

TARGET = untitled3
TEMPLATE = app


SOURCES += main.cpp\
        mainwindow.cpp \
    form.cpp

HEADERS  += mainwindow.h \
    form.h

FORMS    += mainwindow.ui \
    form.ui

form.h:

#ifndef FORM_H
#define FORM_H

#include <QDialog>

namespace Ui {
class Form;
}

class Form : public QDialog
{
    Q_OBJECT

public:
    explicit Form(QWidget *parent = 0);
    ~Form();

protected:
    bool eventFilter(QObject *obj, QEvent *event);

private:
    Ui::Form *ui;
};

#endif // FORM_H

form.cpp:

#include "form.h"
#include "ui_form.h"

Form::Form(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::Form)
{
    ui->setupUi(this);

    parentWidget()->installEventFilter(this);
}

Form::~Form()
{
    delete ui;
}

bool Form::eventFilter(QObject *obj, QEvent *event)
{
    return QObject::eventFilter(obj, event);
}

mainwindow.h:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

class Form;

namespace Ui {
class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();

private:
    Ui::MainWindow *ui;
    Form *f;
};

#endif // MAINWINDOW_H

mainwindow.cpp:

#include "mainwindow.h"
#include "ui_mainwindow.h"
#include "form.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    f = new Form(this);


    connect(ui->pushButton, SIGNAL(clicked()), f, SLOT(show()));
}

MainWindow::~MainWindow()
{
    delete ui;
}

form.ui:

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>Form</class>
 <widget class="QDialog" name="Form">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>400</width>
    <height>300</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>Dialog</string>
  </property>
  <widget class="QDialogButtonBox" name="buttonBox">
   <property name="geometry">
    <rect>
     <x>30</x>
     <y>240</y>
     <width>341</width>
     <height>32</height>
    </rect>
   </property>
   <property name="orientation">
    <enum>Qt::Horizontal</enum>
   </property>
   <property name="standardButtons">
    <set>QDialogButtonBox::Cancel|QDialogButtonBox::Ok</set>
   </property>
  </widget>
  <widget class="QLabel" name="label">
   <property name="geometry">
    <rect>
     <x>190</x>
     <y>40</y>
     <width>46</width>
     <height>13</height>
    </rect>
   </property>
   <property name="text">
    <string>zz</string>
   </property>
  </widget>
 </widget>
 <resources/>
 <connections>
  <connection>
   <sender>buttonBox</sender>
   <signal>accepted()</signal>
   <receiver>Form</receiver>
   <slot>accept()</slot>
   <hints>
    <hint type="sourcelabel">
     <x>248</x>
     <y>254</y>
    </hint>
    <hint type="destinationlabel">
     <x>157</x>
     <y>274</y>
    </hint>
   </hints>
  </connection>
  <connection>
   <sender>buttonBox</sender>
   <signal>rejected()</signal>
   <receiver>Form</receiver>
   <slot>reject()</slot>
   <hints>
    <hint type="sourcelabel">
     <x>316</x>
     <y>260</y>
    </hint>
    <hint type="destinationlabel">
     <x>286</x>
     <y>274</y>
    </hint>
   </hints>
  </connection>
 </connections>
</ui>

mainwindow.ui:

<?xml version="1.0" encoding="UTF-8"?>
<ui version="4.0">
 <class>MainWindow</class>
 <widget class="QMainWindow" name="MainWindow">
  <property name="geometry">
   <rect>
    <x>0</x>
    <y>0</y>
    <width>400</width>
    <height>300</height>
   </rect>
  </property>
  <property name="windowTitle">
   <string>MainWindow</string>
  </property>
  <widget class="QWidget" name="centralWidget">
   <widget class="QPushButton" name="pushButton">
    <property name="geometry">
     <rect>
      <x>200</x>
      <y>40</y>
      <width>75</width>
      <height>23</height>
     </rect>
    </property>
    <property name="text">
     <string>Push</string>
    </property>
   </widget>
  </widget>
  <widget class="QMenuBar" name="menuBar">
   <property name="geometry">
    <rect>
     <x>0</x>
     <y>0</y>
     <width>400</width>
     <height>21</height>
    </rect>
   </property>
  </widget>
  <widget class="QToolBar" name="mainToolBar">
   <attribute name="toolBarArea">
    <enum>TopToolBarArea</enum>
   </attribute>
   <attribute name="toolBarBreak">
    <bool>false</bool>
   </attribute>
  </widget>
  <widget class="QStatusBar" name="statusBar"/>
 </widget>
 <layoutdefault spacing="6" margin="11"/>
 <resources/>
 <connections/>
</ui>

main.cpp:

#include "mainwindow.h"
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();

    return a.exec();
}

The result is that the child widget loses focus but always stays on top of the parent widget. Let me know if it is what you are looking for.