Implement initialization of video devices on the first connection

The problem is that VideoDevices are created and managed by
QPlatformMediaIntegration, but signals are connected to
QPlatformMediaDevices.
A possible redesign is here
codereview.qt-project.org/c/qt/qtmultimedia/+/484647,
but the concern is that it's a bit of controversy with the initial idea.

Current patchs solves the poblem directly and covers with UTs.
Idea of the patch: let's handle connection to
QMediaDevices::videoInputsChanged and initialize
QPlatformMediaIntegration and video devices connection.
I propose postpone initialization because users don't expect
us doing any serious magic just on the signal connection.

The UTs were slightly refactored in order to test the case.

Pick-to: 6.6 6.5
Change-Id: I0ca3dfb2126daf69746380fa65096d9d05327f5e
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>

1 files changed, 14 insertions, 2 deletions

diff --git a/src/multimedia/platform/qplatformmediadevices.cpp b/src/multimedia/platform/qplatformmediadevices.cpp
index 09c26a670..f971fb4c3 100644
--- a/src/multimedia/platform/qplatformmediadevices.cpp
+++ b/src/multimedia/platform/qplatformmediadevices.cpp
@@ -2,11 +2,13 @@
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
 
 #include "qplatformmediadevices_p.h"
+#include "qplatformmediaintegration_p.h"
 #include "qmediadevices.h"
 #include "qaudiodevice.h"
 #include "qcameradevice.h"
 #include "qaudiosystem_p.h"
 #include "qaudiodevice.h"
+#include "qplatformvideodevices_p.h"
 
 #include <qmutex.h>
 #include <qloggingcategory.h>
@@ -75,8 +77,18 @@ QPlatformMediaDevices *QPlatformMediaDevices::instance()
 }
 
 
-QPlatformMediaDevices::QPlatformMediaDevices()
-{}
+QPlatformMediaDevices::QPlatformMediaDevices() = default;
+
+void QPlatformMediaDevices::initVideoDevicesConnection() {
+    std::call_once(m_videoDevicesConnectionFlag, [this]() {
+        QMetaObject::invokeMethod(this, [this]() {
+            auto videoDevices = QPlatformMediaIntegration::instance()->videoDevices();
+            if (videoDevices)
+                connect(videoDevices, &QPlatformVideoDevices::videoInputsChanged, this,
+                        &QPlatformMediaDevices::videoInputsChanged);
+        }, Qt::QueuedConnection);
+    });
+}
 
 void QPlatformMediaDevices::setDevices(QPlatformMediaDevices *devices)
 {