Add example showing the benefits of using bindable properties

Added two examples for modeling a subscription service: signal/slot
connection-based and bindable property-based. The examples are based
on the example from Fabian's Qt WS talk about the bindable properties.

Pick-to: 6.2
Task-number: QTBUG-97655
Change-Id: I0345913b8b6e5c40b8477e128d36483598bdfcaa
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

7 files changed, 510 insertions, 0 deletions

diff --git a/examples/corelib/bindableproperties/bindablesubscription/CMakeLists.txt b/examples/corelib/bindableproperties/bindablesubscription/CMakeLists.txt
new file mode 100644
index 0000000000..b2909589a5
--- /dev/null
+++ b/examples/corelib/bindableproperties/bindablesubscription/CMakeLists.txt
@@ -0,0 +1,53 @@
+cmake_minimum_required(VERSION 3.16)
+project(bindablesubscription LANGUAGES CXX)
+
+set(CMAKE_INCLUDE_CURRENT_DIR ON)
+
+set(CMAKE_AUTOMOC ON)
+set(CMAKE_AUTORCC ON)
+set(CMAKE_AUTOUIC ON)
+
+if(NOT DEFINED INSTALL_EXAMPLESDIR)
+  set(INSTALL_EXAMPLESDIR "examples")
+endif()
+
+set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/corelib/bindableproperties/bindablesubscription")
+
+find_package(Qt6 COMPONENTS Core)
+find_package(Qt6 COMPONENTS Gui)
+find_package(Qt6 COMPONENTS Widgets)
+
+qt_add_executable(bindablesubscription
+    ../shared/subscriptionwindow.cpp ../shared/subscriptionwindow.h ../shared/subscriptionwindow.ui
+    main.cpp
+    main.cpp
+    bindablesubscription.cpp bindablesubscription.h
+    bindableuser.cpp bindableuser.h
+)
+target_link_libraries(bindablesubscription PUBLIC
+    Qt::Core
+    Qt::Gui
+    Qt::Widgets
+)
+
+# Resources:
+set(countries_resource_files
+    "../shared/finland.png"
+    "../shared/germany.png"
+    "../shared/norway.png"
+)
+
+qt6_add_resources(bindablesubscription "countries"
+    PREFIX
+        "/"
+    BASE
+        "../shared"
+    FILES
+        ${countries_resource_files}
+)
+
+install(TARGETS bindablesubscription
+    RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
+    BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
+    LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
+)
diff --git a/examples/corelib/bindableproperties/bindablesubscription/bindablesubscription.cpp b/examples/corelib/bindableproperties/bindablesubscription/bindablesubscription.cpp
new file mode 100644
index 0000000000..d962216cd9
--- /dev/null
+++ b/examples/corelib/bindableproperties/bindablesubscription/bindablesubscription.cpp
@@ -0,0 +1,90 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "bindablesubscription.h"
+#include "bindableuser.h"
+
+BindableSubscription::BindableSubscription(BindableUser *user) : m_user(user)
+{
+    Q_ASSERT(user);
+
+    m_price.setBinding([this] { return qRound(calculateDiscount() * m_duration * basePrice()); });
+
+    m_isValid.setBinding([this] {
+        return m_user->country() != BindableUser::None && m_user->age() > 12;
+    });
+}
+
+void BindableSubscription::setDuration(Duration newDuration)
+{
+    m_duration = newDuration;
+}
+
+double BindableSubscription::calculateDiscount() const
+{
+    switch (m_duration) {
+    case Monthly:
+        return 1;
+    case Quarterly:
+        return 0.9;
+    case Yearly:
+        return 0.6;
+    }
+    Q_ASSERT(false);
+    return -1;
+}
+
+int BindableSubscription::basePrice() const
+{
+    if (m_user->country() == BindableUser::None)
+        return 0;
+
+    return (m_user->country() == BindableUser::Norway) ? 100 : 80;
+}
diff --git a/examples/corelib/bindableproperties/bindablesubscription/bindablesubscription.h b/examples/corelib/bindableproperties/bindablesubscription/bindablesubscription.h
new file mode 100644
index 0000000000..86dd0bdf26
--- /dev/null
+++ b/examples/corelib/bindableproperties/bindablesubscription/bindablesubscription.h
@@ -0,0 +1,87 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef BINDABLESUBSCRIPTION_H
+#define BINDABLESUBSCRIPTION_H
+
+#include <QPointer>
+#include <QProperty>
+
+class BindableUser;
+
+class BindableSubscription
+{
+public:
+    enum Duration { Monthly = 1, Quarterly = 4, Yearly = 12 };
+
+    BindableSubscription(BindableUser *user);
+    BindableSubscription(const BindableSubscription &) = delete;
+
+    int price() const { return m_price; }
+    QBindable<int> bindablePrice() { return &m_price; }
+
+    Duration duration() const { return m_duration; }
+    void setDuration(Duration newDuration);
+    QBindable<Duration> bindableDuration() { return &m_duration; }
+
+    bool isValid() const { return m_isValid; }
+    QBindable<bool> bindableIsValid() { return &m_isValid; }
+
+private:
+    double calculateDiscount() const;
+    int basePrice() const;
+
+    BindableUser *m_user;
+    QProperty<Duration> m_duration { Monthly };
+    QProperty<int> m_price { 0 };
+    QProperty<bool> m_isValid { false };
+};
+
+#endif // BNDABLESUBSCRIPTION_H
diff --git a/examples/corelib/bindableproperties/bindablesubscription/bindablesubscription.pro b/examples/corelib/bindableproperties/bindablesubscription/bindablesubscription.pro
new file mode 100644
index 0000000000..321a1226c4
--- /dev/null
+++ b/examples/corelib/bindableproperties/bindablesubscription/bindablesubscription.pro
@@ -0,0 +1,22 @@
+QT += widgets
+TARGET = bindablesubscription
+
+SOURCES += main.cpp \
+    bindablesubscription.cpp \
+    bindableuser.cpp \
+    ../shared/subscriptionwindow.cpp
+
+target.path = $$[QT_INSTALL_EXAMPLES]/corelib/bindableproperties/bindablesubscription
+INSTALLS += target
+
+FORMS += \
+    ../shared/subscriptionwindow.ui
+
+HEADERS += \
+    bindablesubscription.h \
+    bindableuser.h \
+    ../shared/subscriptionwindow.h
+
+RESOURCES += \
+    ../shared/countries.qrc
+
diff --git a/examples/corelib/bindableproperties/bindablesubscription/bindableuser.cpp b/examples/corelib/bindableproperties/bindablesubscription/bindableuser.cpp
new file mode 100644
index 0000000000..fc651c2579
--- /dev/null
+++ b/examples/corelib/bindableproperties/bindablesubscription/bindableuser.cpp
@@ -0,0 +1,61 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "bindableuser.h"
+
+void BindableUser::setCountry(Country country)
+{
+    m_country = country;
+}
+
+void BindableUser::setAge(int age)
+{
+    m_age = age;
+}
diff --git a/examples/corelib/bindableproperties/bindablesubscription/bindableuser.h b/examples/corelib/bindableproperties/bindablesubscription/bindableuser.h
new file mode 100644
index 0000000000..1c37078076
--- /dev/null
+++ b/examples/corelib/bindableproperties/bindablesubscription/bindableuser.h
@@ -0,0 +1,81 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef BINDABLEUSER_H
+#define BINDABLEUSER_H
+
+#include <QProperty>
+
+class BindableUser
+{
+public:
+    enum Country {
+        None,
+        Finland,
+        Germany,
+        Norway,
+    };
+
+    BindableUser() = default;
+    BindableUser(const BindableUser &) = delete;
+
+    Country country() const { return m_country; }
+    void setCountry(Country country);
+    QBindable<Country> bindableCountry() { return &m_country; }
+
+    int age() const { return m_age; }
+    void setAge(int age);
+    QBindable<int> bindableAge() { return &m_age; }
+
+private:
+    QProperty<Country> m_country { None };
+    QProperty<int> m_age { 0 };
+};
+#endif // BINDABLEUSER_H
diff --git a/examples/corelib/bindableproperties/bindablesubscription/main.cpp b/examples/corelib/bindableproperties/bindablesubscription/main.cpp
new file mode 100644
index 0000000000..2ee39c5bb5
--- /dev/null
+++ b/examples/corelib/bindableproperties/bindablesubscription/main.cpp
@@ -0,0 +1,116 @@
+/****************************************************************************
+**
+** Copyright (C) 2021 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the examples of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "../shared/subscriptionwindow.h"
+#include "bindablesubscription.h"
+#include "bindableuser.h"
+
+#include <QApplication>
+#include <QButtonGroup>
+#include <QLabel>
+#include <QPushButton>
+#include <QRadioButton>
+#include <QSpinBox>
+
+int main(int argc, char *argv[])
+{
+    QApplication a(argc, argv);
+    BindableUser user;
+    BindableSubscription subscription(&user);
+
+    SubscriptionWindow w;
+
+    // Initialize subscription data
+    QRadioButton *monthly = w.findChild<QRadioButton *>("btnMonthly");
+    QObject::connect(monthly, &QRadioButton::clicked, [&] {
+        subscription.setDuration(BindableSubscription::Monthly);
+    });
+    QRadioButton *quarterly = w.findChild<QRadioButton *>("btnQuarterly");
+    QObject::connect(quarterly, &QRadioButton::clicked, [&] {
+        subscription.setDuration(BindableSubscription::Quarterly);
+    });
+    QRadioButton *yearly = w.findChild<QRadioButton *>("btnYearly");
+    QObject::connect(yearly, &QRadioButton::clicked, [&] {
+        subscription.setDuration(BindableSubscription::Yearly);
+    });
+
+    // Initialize user data
+    QPushButton *germany = w.findChild<QPushButton *>("btnGermany");
+    QObject::connect(germany, &QPushButton::clicked, [&] {
+        user.setCountry(BindableUser::Germany);
+    });
+    QPushButton *finland = w.findChild<QPushButton *>("btnFinland");
+    QObject::connect(finland, &QPushButton::clicked, [&] {
+        user.setCountry(BindableUser::Finland);
+    });
+    QPushButton *norway = w.findChild<QPushButton *>("btnNorway");
+    QObject::connect(norway, &QPushButton::clicked, [&] {
+        user.setCountry(BindableUser::Norway);
+    });
+
+    QSpinBox *ageSpinBox = w.findChild<QSpinBox *>("ageSpinBox");
+    QObject::connect(ageSpinBox, &QSpinBox::valueChanged, [&](int value) {
+        user.setAge(value);
+    });
+
+    QLabel *priceDisplay = w.findChild<QLabel *>("priceDisplay");
+
+    // Track price changes
+    auto priceChangeHandler = subscription.bindablePrice().subscribe([&] {
+        priceDisplay->setText(QString::number(subscription.price()));
+    });
+
+    auto priceValidHandler = subscription.bindableIsValid().subscribe([&] {
+        priceDisplay->setEnabled(subscription.isValid());
+    });
+
+    w.show();
+    return a.exec();
+}