LowEnergyScanner example: migrate to QML Permission API

Update the example to use QML Permission API.
This is not strictly necessary, because the example provides custom
C++ wrappers around Qt Bluetooth classes, and the permission request
was already conveniently implemented there.
However, this example is a good candidate to show QML Permission API
usage with Qt Bluetooth.
That's the reason for the code update, as well as a documentation
improvement.

Fixes: QTBUG-114640
Change-Id: I3ffeb61a83c205724da8b462f930604e1adb26c0
Reviewed-by: Juha Vuolle <juha.vuolle@qt.io>
(cherry picked from commit 92e095a4ff780145d91feae2be33184be4503b40)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

3 files changed, 46 insertions, 29 deletions

diff --git a/examples/bluetooth/lowenergyscanner/Devices.qml b/examples/bluetooth/lowenergyscanner/Devices.qml
index 40afce7f..b41c259d 100644
--- a/examples/bluetooth/lowenergyscanner/Devices.qml
+++ b/examples/bluetooth/lowenergyscanner/Devices.qml
@@ -3,6 +3,7 @@
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
 
 pragma ComponentBehavior: Bound
+import QtCore
 import QtQuick
 
 Rectangle {
@@ -14,6 +15,19 @@ Rectangle {
     width: 300
     height: 600
 
+    function toggleDiscovery() {
+        if (!Device.state) {
+            Device.startDeviceDiscovery()
+            // if startDeviceDiscovery() failed Device.state is not set
+            if (Device.state) {
+                info.dialogText = "Searching..."
+                info.visible = true
+            }
+        } else {
+            Device.stopDeviceDiscovery()
+        }
+    }
+
     onDeviceStateChanged: {
         if (!Device.state)
             info.visible = false
@@ -99,23 +113,32 @@ Rectangle {
         onButtonClick: Device.useRandomAddress = !Device.useRandomAddress
     }
 
+    //! [permission-object]
+    BluetoothPermission {
+        id: permission
+        communicationModes: BluetoothPermission.Access
+        onStatusChanged: {
+            if (permission.status === Qt.PermissionStatus.Denied)
+                Device.update = "Bluetooth permission required"
+            else if (permission.status === Qt.PermissionStatus.Granted)
+                devicesPage.toggleDiscovery()
+        }
+    }
+    //! [permission-object]
+
     Menu {
         id: menu
         anchors.bottom: parent.bottom
         menuWidth: parent.width
         menuHeight: (parent.height / 6)
         menuText: Device.update
+        //! [permission-request]
         onButtonClick: {
-            if (!Device.state) {
-                Device.startDeviceDiscovery()
-                // if startDeviceDiscovery() failed Device.state is not set
-                if (Device.state) {
-                    info.dialogText = "Searching..."
-                    info.visible = true
-                }
-            } else {
-                Device.stopDeviceDiscovery()
-            }
+            if (permission.status === Qt.PermissionStatus.Undetermined)
+                permission.request()
+            else if (permission.status === Qt.PermissionStatus.Granted)
+                devicesPage.toggleDiscovery()
         }
+        //! [permission-request]
     }
 }
diff --git a/examples/bluetooth/lowenergyscanner/device.cpp b/examples/bluetooth/lowenergyscanner/device.cpp
index ae74d54c..93960c31 100644
--- a/examples/bluetooth/lowenergyscanner/device.cpp
+++ b/examples/bluetooth/lowenergyscanner/device.cpp
@@ -48,22 +48,6 @@ Device::~Device()
 
 void Device::startDeviceDiscovery()
 {
-#if QT_CONFIG(permissions)
-    //! [les-bluetooth-permission]
-    QBluetoothPermission permission;
-    permission.setCommunicationModes(QBluetoothPermission::Access);
-    const auto permissionStatus = qApp->checkPermission(permission);
-    if (permissionStatus == Qt::PermissionStatus::Undetermined) {
-        qApp->requestPermission(permission, this, &Device::startDeviceDiscovery);
-        return;
-    }
-    if (permissionStatus == Qt::PermissionStatus::Denied) {
-        setUpdate("Bluetooth permission required.");
-        return;
-    }
-    //! [les-bluetooth-permission]
-#endif // QT_CONFIG(permissions)
-
     qDeleteAll(devices);
     devices.clear();
     emit devicesUpdated();
diff --git a/examples/bluetooth/lowenergyscanner/doc/src/lowenergyscanner.qdoc b/examples/bluetooth/lowenergyscanner/doc/src/lowenergyscanner.qdoc
index df7f8484..d7f76c4d 100644
--- a/examples/bluetooth/lowenergyscanner/doc/src/lowenergyscanner.qdoc
+++ b/examples/bluetooth/lowenergyscanner/doc/src/lowenergyscanner.qdoc
@@ -34,10 +34,20 @@
     \include examples-run.qdocinc
 
     \section1 Requesting Permission to use Bluetooth
-    Before the application can start using Bluetooth, we have to check Bluetooth
-    permission, and if its status is not determined yet, request this permission:
 
-    \snippet lowenergyscanner/device.cpp les-bluetooth-permission
+    On certain platforms, it is required to explicitly grant permissions for
+    using Bluetooth. The example uses \c BluetoothPermission QML object to
+    check and request the permissions, if required:
+
+    \snippet lowenergyscanner/Devices.qml permission-object
+
+    The permission request dialog is triggered when the user tries to start
+    the device discovery, and the permission status is \c {Undetermined}:
+
+    \snippet lowenergyscanner/Devices.qml permission-request
+
+    The device discovery starts if the permission is granted by the user.
+    Otherwise the application is non-functional.
 
     \section1 Scanning for Devices