Improve QtConcurrent ImageScaling example to demo new features

In order to demonstrate the new functionality, changed the example to
download the images from the network, scale and show them by attaching
different continuations to QFuture. Because QtConcurrent::map is not
used anymore, removed the suspension functionality (supporting
suspension of download would complicate the logic).

Task-number: QTBUG-87205
Change-Id: I5a48b63195d28025ae8c5de28bc6d6178dad03db
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

9 files changed, 618 insertions, 68 deletions

diff --git a/examples/qtconcurrent/imagescaling/CMakeLists.txt b/examples/qtconcurrent/imagescaling/CMakeLists.txt
index b1065e877b..caca16da12 100644
--- a/examples/qtconcurrent/imagescaling/CMakeLists.txt
+++ b/examples/qtconcurrent/imagescaling/CMakeLists.txt
@@ -19,8 +19,10 @@ find_package(Qt6 COMPONENTS Core)
 find_package(Qt6 COMPONENTS Gui)
 find_package(Qt6 COMPONENTS Concurrent)
 find_package(Qt6 COMPONENTS Widgets)
+find_package(Qt6 COMPONENTS Network)
 
 qt_add_executable(imagescaling
+    downloaddialog.cpp downloaddialog.h downloaddialog.ui
     imagescaling.cpp imagescaling.h
     main.cpp
 )
@@ -32,6 +34,7 @@ target_link_libraries(imagescaling PUBLIC
     Qt::Concurrent
     Qt::Core
     Qt::Gui
+    Qt::Network
     Qt::Widgets
 )
 
diff --git a/examples/qtconcurrent/imagescaling/doc/images/imagescaling_example.png b/examples/qtconcurrent/imagescaling/doc/images/imagescaling_example.png
index 7c6794132a..a3860e1974 100644
--- a/examples/qtconcurrent/imagescaling/doc/images/imagescaling_example.png
+++ b/examples/qtconcurrent/imagescaling/doc/images/imagescaling_example.png
diff --git a/examples/qtconcurrent/imagescaling/doc/src/qtconcurrent-imagescaling.qdoc b/examples/qtconcurrent/imagescaling/doc/src/qtconcurrent-imagescaling.qdoc
index 0134f0f8e8..a919b7e2ed 100644
--- a/examples/qtconcurrent/imagescaling/doc/src/qtconcurrent-imagescaling.qdoc
+++ b/examples/qtconcurrent/imagescaling/doc/src/qtconcurrent-imagescaling.qdoc
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2020 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the documentation of the Qt Toolkit.
@@ -28,10 +28,142 @@
 /*!
     \example imagescaling
     \title Image Scaling Example
-    \brief Demonstrates how to asynchronously scale images.
+    \brief Demonstrates how to asynchronously download and scale images.
     \ingroup qtconcurrentexamples
     \image imagescaling_example.png
 
-    The QtConcurrent Map example shows how to use the asynchronous
-    QtConcurrent API to load and scale a collection of images.
+    This example shows how to use the QFuture and QPromise classes to download a
+    collection of images from the network and scale them, without blocking the UI.
+
+    The application consists of the the following steps:
+
+    \list 1
+    \li Download images form the list of URLs specified by the user.
+    \li Scale the images.
+    \li Show the scaled images in a grid layout.
+    \endlist
+
+    Let's start with the download:
+
+    \snippet imagescaling/imagescaling.cpp 8
+
+    The \c download() method takes a list of URLs and returns a QFuture. The QFuture
+    stores the byte array data received for each downloaded image. To store the data
+    inside the QFuture, we create a QPromise object and report that it has started to
+    indicate the start of the download:
+
+    \snippet imagescaling/imagescaling.cpp 9
+    \dots
+    \snippet imagescaling/imagescaling.cpp 13
+
+    The future associated with the promise is returned to the caller.
+
+    Without going into details yet, let's note that the promise object is wrapped
+    inside a QSharedPointer. This will be explained later.
+
+    We use QNetworkAccessManager to send network requests and download data for each
+    url:
+
+    \snippet imagescaling/imagescaling.cpp 10
+
+    And here starts the interesting part:
+
+    \dots
+    \snippet imagescaling/imagescaling.cpp 11
+    \dots
+
+    Instead of connecting to QNetworkReply's signals using the QObject::connect()
+    method, we use QtFuture::connect(). It works similar to QObject::connect(), but
+    returns a QFuture object, that becomes available as soon as the
+    QNetworkReply::finished() signal is emitted. This allows us to attach continuations
+    and failure handlers, as it is done in the example.
+
+    In the continuation attached via \b{.then()}, we check if the user has requested to
+    cancel the download. If that's the case, we stop processing the request. By calling
+    the \c QPromise::finish() method, we notify the user that processing has been finished.
+    In case the network request has ended with an error, we throw an exception. The
+    exception will be handled in the failure handler attached using the \b{.onFailed()}
+    method. Note that we have two failure handlers: the first one captures the network
+    errors, the second one all other exceptions thrown during the execution. Both handlers
+    save the exception inside the promise object (to be handled by the caller of the
+    \c download() method) and report that the computation has finished. Also note that,
+    for simplicity, in case of an error we interrupt all pending downloads.
+
+    If the request has not been canceled and no error occurred, we read the data from
+    the network reply and add it to the list of results of the promise object:
+
+    \dots
+    \snippet imagescaling/imagescaling.cpp 12
+    \dots
+
+    If the number of results stored inside the promise object is equal to the number
+    of the \c {url}s to be downloaded, there are no more requests to process, so we also
+    report that the promise has finished.
+
+    As mentioned earlier, we've wrapped the promise inside a QSharedPointer.
+    Since the promise object is shared between handlers connected to each network reply,
+    we need to copy and use the promise object in multiple places simultaneously. Hence,
+    a QSharedPointer is used.
+
+    \c download() method is called from the \c QImage::process method. It is invoked
+    when the user presses the \e {"Add URLs"} button:
+
+    \dots
+    \snippet imagescaling/imagescaling.cpp 1
+    \dots
+
+    After clearing the possible leftovers from previous download, we create a dialog
+    so that the user can specify the URLs for the images to download. Based on the
+    specified URL count, we initialize the layout where the images will be shown and
+    start the download. The future returned by the \c download() method is saved, so that
+    the user can cancel the download if needed:
+
+    \snippet imagescaling/imagescaling.cpp 3
+    \dots
+
+    Next, we attach a continuation to handle the scaling step:
+
+    \snippet imagescaling/imagescaling.cpp 4
+    \dots
+
+    Since the scaling may be computationally heavy, and we don't want to block the main
+    thread, we pass the \c QtFuture::Launch::Async option, to launch the scaling step in
+    a new thread.
+
+    The \c scaled() method returns a list of the scaled images to the next step, which
+    takes care of showing images in the layout:
+
+    \dots
+    \snippet imagescaling/imagescaling.cpp 5
+    \dots
+
+    Note that showImages() needs to be invoked from the main thread, so we call it through
+    QMetaObject::invokeMethod().
+
+    Then we add cancellation and failure handlers:
+
+    \dots
+    \snippet imagescaling/imagescaling.cpp 6
+
+    The handler attached via the \c .onCanceled() method will be called if the user has
+    pressed the \e "Cancel" button:
+
+    \dots
+    \snippet imagescaling/imagescaling.cpp 2
+    \dots
+
+    The \c cancel() method simply aborts all the pending requests:
+
+    \snippet imagescaling/imagescaling.cpp 7
+
+    The handlers attached via \c .onFailed() method will be called in case an
+    error occurred during one of the previous steps. For example, if a network error
+    has been saved inside the promise during the download step, it will be propagated to
+    the handler that takes \c QNetworkReply::NetworkError as argument. A failure can
+    happen also during the scaling step:
+
+    \snippet imagescaling/imagescaling.cpp 14
+
+    The rest of the code is straightforward, you can check the example project for
+    more details.
 */
diff --git a/examples/qtconcurrent/imagescaling/downloaddialog.cpp b/examples/qtconcurrent/imagescaling/downloaddialog.cpp
new file mode 100644
index 0000000000..2f2f901b0e
--- /dev/null
+++ b/examples/qtconcurrent/imagescaling/downloaddialog.cpp
@@ -0,0 +1,87 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 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 "downloaddialog.h"
+#include "ui_downloaddialog.h"
+
+#include <QUrl>
+
+DownloadDialog::DownloadDialog(QWidget *parent) : QDialog(parent), ui(new Ui::DownloadDialog)
+{
+    ui->setupUi(this);
+
+    ui->urlLineEdit->setPlaceholderText(tr("Enter the URL of an image to download"));
+
+    connect(ui->addUrlButton, &QPushButton::clicked, this, [this] {
+        const auto text = ui->urlLineEdit->text();
+        if (!text.isEmpty()) {
+            ui->urlListWidget->addItem(text);
+            ui->urlLineEdit->clear();
+        }
+    });
+    connect(ui->urlListWidget, &QListWidget::itemSelectionChanged, this, [this] {
+        ui->removeUrlButton->setEnabled(!ui->urlListWidget->selectedItems().empty());
+    });
+    connect(ui->clearUrlsButton, &QPushButton::clicked, ui->urlListWidget, &QListWidget::clear);
+    connect(ui->removeUrlButton, &QPushButton::clicked, this,
+            [this] { qDeleteAll(ui->urlListWidget->selectedItems()); });
+}
+
+DownloadDialog::~DownloadDialog()
+{
+    delete ui;
+}
+
+QList<QUrl> DownloadDialog::getUrls() const
+{
+    QList<QUrl> urls;
+    for (auto row = 0; row < ui->urlListWidget->count(); ++row)
+        urls.push_back(QUrl(ui->urlListWidget->item(row)->text()));
+    return urls;
+}
diff --git a/examples/qtconcurrent/imagescaling/downloaddialog.h b/examples/qtconcurrent/imagescaling/downloaddialog.h
new file mode 100644
index 0000000000..9e5d478d7d
--- /dev/null
+++ b/examples/qtconcurrent/imagescaling/downloaddialog.h
@@ -0,0 +1,75 @@
+/****************************************************************************
+**
+** Copyright (C) 2020 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 DOWNLOADDIALOG_H
+#define DOWNLOADDIALOG_H
+
+#include <QDialog>
+
+QT_BEGIN_NAMESPACE
+namespace Ui {
+class DownloadDialog;
+}
+QT_END_NAMESPACE
+
+class DownloadDialog : public QDialog
+{
+    Q_OBJECT
+
+public:
+    explicit DownloadDialog(QWidget *parent = nullptr);
+    ~DownloadDialog();
+
+    QList<QUrl> getUrls() const;
+
+private:
+    Ui::DownloadDialog *ui;
+};
+
+#endif // DOWNLOADDIALOG_H
diff --git a/examples/qtconcurrent/imagescaling/downloaddialog.ui b/examples/qtconcurrent/imagescaling/downloaddialog.ui
new file mode 100644
index 0000000000..c85a063568
--- /dev/null
+++ b/examples/qtconcurrent/imagescaling/downloaddialog.ui
@@ -0,0 +1,119 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<ui version="4.0">
+ <class>DownloadDialog</class>
+ <widget class="QDialog" name="DownloadDialog">
+  <property name="geometry">
+   <rect>
+    <x>0</x>
+    <y>0</y>
+    <width>489</width>
+    <height>333</height>
+   </rect>
+  </property>
+  <property name="windowTitle">
+   <string>Dialog</string>
+  </property>
+  <layout class="QVBoxLayout" name="verticalLayout_5">
+   <item>
+    <layout class="QHBoxLayout" name="horizontalLayout_4">
+     <item>
+      <layout class="QVBoxLayout" name="verticalLayout_3">
+       <item>
+        <widget class="QLineEdit" name="urlLineEdit"/>
+       </item>
+       <item>
+        <widget class="QListWidget" name="urlListWidget"/>
+       </item>
+      </layout>
+     </item>
+     <item>
+      <layout class="QVBoxLayout" name="verticalLayout_4">
+       <item>
+        <widget class="QPushButton" name="addUrlButton">
+         <property name="text">
+          <string>Add URL</string>
+         </property>
+        </widget>
+       </item>
+       <item>
+        <widget class="QPushButton" name="removeUrlButton">
+         <property name="enabled">
+          <bool>false</bool>
+         </property>
+         <property name="text">
+          <string>Remove URL</string>
+         </property>
+        </widget>
+       </item>
+       <item>
+        <widget class="QPushButton" name="clearUrlsButton">
+         <property name="text">
+          <string>Clear</string>
+         </property>
+        </widget>
+       </item>
+       <item>
+        <spacer name="verticalSpacer_2">
+         <property name="orientation">
+          <enum>Qt::Vertical</enum>
+         </property>
+         <property name="sizeHint" stdset="0">
+          <size>
+           <width>20</width>
+           <height>40</height>
+          </size>
+         </property>
+        </spacer>
+       </item>
+      </layout>
+     </item>
+    </layout>
+   </item>
+   <item>
+    <widget class="QDialogButtonBox" name="buttonBox">
+     <property name="orientation">
+      <enum>Qt::Horizontal</enum>
+     </property>
+     <property name="standardButtons">
+      <set>QDialogButtonBox::Cancel|QDialogButtonBox::Ok</set>
+     </property>
+    </widget>
+   </item>
+  </layout>
+ </widget>
+ <resources/>
+ <connections>
+  <connection>
+   <sender>buttonBox</sender>
+   <signal>accepted()</signal>
+   <receiver>DownloadDialog</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>DownloadDialog</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>
diff --git a/examples/qtconcurrent/imagescaling/imagescaling.cpp b/examples/qtconcurrent/imagescaling/imagescaling.cpp
index 65ec16e383..59664f8a58 100644
--- a/examples/qtconcurrent/imagescaling/imagescaling.cpp
+++ b/examples/qtconcurrent/imagescaling/imagescaling.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2020 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the examples of the Qt Toolkit.
@@ -48,106 +48,219 @@
 **
 ****************************************************************************/
 #include "imagescaling.h"
+#include "downloaddialog.h"
+
+#include <QNetworkReply>
 
 #include <qmath.h>
 
 #include <functional>
 
-Images::Images(QWidget *parent)
-    : QWidget(parent)
+Images::Images(QWidget *parent) : QWidget(parent), downloadDialog(new DownloadDialog())
 {
-    setWindowTitle(tr("Image loading and scaling example"));
+    setWindowTitle(tr("Image downloading and scaling example"));
     resize(800, 600);
 
-    imageScaling = new QFutureWatcher<QImage>(this);
-    connect(imageScaling, &QFutureWatcher<QImage>::resultReadyAt, this, &Images::showImage);
-    connect(imageScaling, &QFutureWatcher<QImage>::finished, this, &Images::finished);
-
-    openButton = new QPushButton(tr("Open Images"));
-    connect(openButton, &QPushButton::clicked, this, &Images::open);
+    addUrlsButton = new QPushButton(tr("Add URLs"));
+//! [1]
+    connect(addUrlsButton, &QPushButton::clicked, this, &Images::process);
+//! [1]
 
     cancelButton = new QPushButton(tr("Cancel"));
     cancelButton->setEnabled(false);
-    connect(cancelButton, &QPushButton::clicked, imageScaling, &QFutureWatcher<QImage>::cancel);
-
-    pauseButton = new QPushButton(tr("Pause/Resume"));
-    pauseButton->setEnabled(false);
-    connect(pauseButton, &QPushButton::clicked, imageScaling, &QFutureWatcher<QImage>::toggleSuspended);
+//! [2]
+    connect(cancelButton, &QPushButton::clicked, this, &Images::cancel);
+//! [2]
 
     QHBoxLayout *buttonLayout = new QHBoxLayout();
-    buttonLayout->addWidget(openButton);
+    buttonLayout->addWidget(addUrlsButton);
     buttonLayout->addWidget(cancelButton);
-    buttonLayout->addWidget(pauseButton);
     buttonLayout->addStretch();
 
+    statusBar = new QStatusBar();
+
     imagesLayout = new QGridLayout();
 
     mainLayout = new QVBoxLayout();
     mainLayout->addLayout(buttonLayout);
     mainLayout->addLayout(imagesLayout);
     mainLayout->addStretch();
+    mainLayout->addWidget(statusBar);
     setLayout(mainLayout);
 }
 
 Images::~Images()
 {
-    imageScaling->cancel();
-    imageScaling->waitForFinished();
+    cancel();
+}
+
+//! [3]
+void Images::process()
+{
+    // Clean previous state
+    replies.clear();
+
+    if (downloadDialog->exec() == QDialog::Accepted) {
+
+        const auto urls = downloadDialog->getUrls();
+        if (urls.empty())
+            return;
+
+        cancelButton->setEnabled(true);
+
+        initLayout(urls.size());
+
+        downloadFuture = download(urls);
+        statusBar->showMessage(tr("Downloading..."));
+//! [3]
+
+//! [4]
+        downloadFuture.then([this](auto) { cancelButton->setEnabled(false); })
+                .then(QtFuture::Launch::Async,
+                      [this] {
+                          updateStatus(tr("Scaling..."));
+                          return scaled();
+                      })
+//! [4]
+//! [5]
+                .then([this](const QList<QImage> &scaled) {
+                    QMetaObject::invokeMethod(this, [this, scaled] { showImages(scaled); });
+                    updateStatus(tr("Finished"));
+                })
+//! [5]
+//! [6]
+                .onCanceled([this] { updateStatus(tr("Download has been canceled.")); })
+                .onFailed([this](QNetworkReply::NetworkError error) {
+                    const auto msg = QString("Download finished with error: %1").arg(error);
+                    updateStatus(tr(msg.toStdString().c_str()));
+
+                    // Abort all pending requests
+                    QMetaObject::invokeMethod(this, &Images::abortDownload);
+                })
+                .onFailed([this](const std::exception& ex) {
+                    updateStatus(tr(ex.what()));
+                });
+//! [6]
+    }
+}
+
+//! [7]
+void Images::cancel()
+{
+    statusBar->showMessage(tr("Canceling..."));
+
+    downloadFuture.cancel();
+    abortDownload();
 }
+//! [7]
 
-void Images::open()
+//! [8]
+QFuture<QByteArray> Images::download(const QList<QUrl> &urls)
+//! [8]
 {
-    // Cancel and wait if we are already loading images.
-    if (imageScaling->isRunning()) {
-        imageScaling->cancel();
-        imageScaling->waitForFinished();
+//! [9]
+    QSharedPointer<QPromise<QByteArray>> promise(new QPromise<QByteArray>());
+    promise->start();
+//! [9]
+
+//! [10]
+    for (auto url : urls) {
+        QSharedPointer<QNetworkReply> reply(qnam.get(QNetworkRequest(url)));
+        replies.push_back(reply);
+//! [10]
+
+//! [11]
+        QtFuture::connect(reply.get(), &QNetworkReply::finished).then([=] {
+            if (promise->isCanceled()) {
+                if (!promise->future().isFinished())
+                    promise->finish();
+                return;
+            }
+
+            if (reply->error() != QNetworkReply::NoError) {
+                if (!promise->future().isFinished())
+                    throw reply->error();
+            }
+//! [12]
+            promise->addResult(reply->readAll());
+
+            // Report finished on the last download
+            if (promise->future().resultCount() == urls.size()) {
+                promise->finish();
+            }
+//! [12]
+        }).onFailed([=] (QNetworkReply::NetworkError error) {
+            promise->setException(std::make_exception_ptr(error));
+            promise->finish();
+        }).onFailed([=] {
+            const auto ex = std::make_exception_ptr(
+                        std::runtime_error("Unknown error occurred while downloading."));
+            promise->setException(ex);
+            promise->finish();
+        });
     }
+//! [11]
+
+//! [13]
+    return promise->future();
+}
+//! [13]
 
-    // Show a file open dialog at QStandardPaths::PicturesLocation.
-    QStringList files = QFileDialog::getOpenFileNames(this, tr("Select Images"),
-                            QStandardPaths::writableLocation(QStandardPaths::PicturesLocation),
-                            "*.jpg *.png");
+//! [14]
+QList<QImage> Images::scaled() const
+{
+    QList<QImage> scaled;
+    const auto data = downloadFuture.results();
+    for (auto imgData : data) {
+        QImage image;
+        image.loadFromData(imgData);
+        if (image.isNull())
+            throw std::runtime_error("Failed to load image.");
 
-    if (files.isEmpty())
-        return;
+        scaled.push_back(image.scaled(100, 100, Qt::KeepAspectRatio));
+    }
 
-    const int imageSize = 100;
+    return scaled;
+}
+//! [14]
 
-    // Do a simple layout.
-    qDeleteAll(labels);
+void Images::showImages(const QList<QImage> &images)
+{
+    for (int i = 0; i < images.size(); ++i) {
+        labels[i]->setAlignment(Qt::AlignCenter);
+        labels[i]->setPixmap(QPixmap::fromImage(images[i]));
+    }
+}
+
+void Images::initLayout(qsizetype count)
+{
+    // Clean old images
+    QLayoutItem *child;
+    while ((child = imagesLayout->takeAt(0)) != nullptr) {
+        child->widget()->setParent(nullptr);
+        delete child;
+    }
     labels.clear();
 
-    int dim = qSqrt(qreal(files.count())) + 1;
+    // Init the images layout for the new images
+    const auto dim = int(qSqrt(qreal(count))) + 1;
     for (int i = 0; i < dim; ++i) {
         for (int j = 0; j < dim; ++j) {
             QLabel *imageLabel = new QLabel;
-            imageLabel->setFixedSize(imageSize,imageSize);
-            imagesLayout->addWidget(imageLabel,i,j);
+            imageLabel->setFixedSize(100, 100);
+            imagesLayout->addWidget(imageLabel, i, j);
             labels.append(imageLabel);
         }
     }
-
-    std::function<QImage(const QString&)> scale = [&](const QString &imageFileName) {
-        QImage image(imageFileName);
-        return image.scaled(QSize(imageSize, imageSize), Qt::IgnoreAspectRatio, Qt::SmoothTransformation);
-    };
-
-    // Use mapped to run the thread safe scale function on the files.
-    imageScaling->setFuture(QtConcurrent::mapped(files, scale));
-
-    openButton->setEnabled(false);
-    cancelButton->setEnabled(true);
-    pauseButton->setEnabled(true);
 }
 
-void Images::showImage(int num)
+void Images::updateStatus(const QString &msg)
 {
-    labels[num]->setPixmap(QPixmap::fromImage(imageScaling->resultAt(num)));
+    QMetaObject::invokeMethod(this, [this, msg] { statusBar->showMessage(msg); });
 }
 
-void Images::finished()
+void Images::abortDownload()
 {
-    openButton->setEnabled(true);
-    cancelButton->setEnabled(false);
-    pauseButton->setEnabled(false);
+    for (auto reply : replies)
+        reply->abort();
 }
diff --git a/examples/qtconcurrent/imagescaling/imagescaling.h b/examples/qtconcurrent/imagescaling/imagescaling.h
index fe9c801387..0c0d90870e 100644
--- a/examples/qtconcurrent/imagescaling/imagescaling.h
+++ b/examples/qtconcurrent/imagescaling/imagescaling.h
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2020 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the examples of the Qt Toolkit.
@@ -52,25 +52,40 @@
 
 #include <QtWidgets>
 #include <QtConcurrent>
+#include <QNetworkAccessManager>
 
+class DownloadDialog;
 class Images : public QWidget
 {
 Q_OBJECT
 public:
     Images(QWidget *parent = nullptr);
     ~Images();
+
+    void initLayout(qsizetype count);
+
+    QFuture<QByteArray> download(const QList<QUrl> &urls);
+    QList<QImage> scaled() const;
+    void updateStatus(const QString &msg);
+    void showImages(const QList<QImage> &images);
+    void abortDownload();
+
 public slots:
-    void open();
-    void showImage(int num);
-    void finished();
+    void process();
+    void cancel();
+
 private:
-    QPushButton *openButton;
+    QPushButton *addUrlsButton;
     QPushButton *cancelButton;
-    QPushButton *pauseButton;
     QVBoxLayout *mainLayout;
     QList<QLabel *> labels;
     QGridLayout *imagesLayout;
-    QFutureWatcher<QImage> *imageScaling;
+    QStatusBar *statusBar;
+    DownloadDialog *downloadDialog;
+
+    QNetworkAccessManager qnam;
+    QList<QSharedPointer<QNetworkReply>> replies;
+    QFuture<QByteArray> downloadFuture;
 };
 
 #endif // IMAGESCALING_H
diff --git a/examples/qtconcurrent/imagescaling/imagescaling.pro b/examples/qtconcurrent/imagescaling/imagescaling.pro
index 127fa532c9..9b458adfea 100644
--- a/examples/qtconcurrent/imagescaling/imagescaling.pro
+++ b/examples/qtconcurrent/imagescaling/imagescaling.pro
@@ -1,8 +1,14 @@
-QT += concurrent widgets
+QT += concurrent widgets network
+CONFIG += exceptions
 requires(qtConfig(filedialog))
 
-SOURCES += main.cpp imagescaling.cpp
-HEADERS += imagescaling.h
+SOURCES += main.cpp imagescaling.cpp \
+    downloaddialog.cpp
+HEADERS += imagescaling.h \
+    downloaddialog.h
 
 target.path = $$[QT_INSTALL_EXAMPLES]/qtconcurrent/imagescaling
 INSTALLS += target
+
+FORMS += \
+    downloaddialog.ui