Introduce QQmlApplicationEngine::loadFromModule

This allow instantiating QML types via their module and typename. It
simply exposes the underlying functionality of
QQmlComponent::loadFromModule.
Also add the corresponding convenience constructor.

This commit also does some minor refactoring so that functionality can
be shared between load and loadFromModule.

[ChangeLog][QtQml][QQmlApplicationEngine] It is now possible to load QML
types via their module and type name.

Fixes: QTBUG-97156
Change-Id: Iee812db269d27e4db4b10117ed2570272a7cc40c
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

5 files changed, 81 insertions, 16 deletions

diff --git a/src/qml/qml/qqmlapplicationengine.cpp b/src/qml/qml/qqmlapplicationengine.cpp
index 08564e1cc2..45f7043336 100644
--- a/src/qml/qml/qqmlapplicationengine.cpp
+++ b/src/qml/qml/qqmlapplicationengine.cpp
@@ -23,6 +23,14 @@ QQmlApplicationEnginePrivate::~QQmlApplicationEnginePrivate()
 {
 }
 
+void QQmlApplicationEnginePrivate::ensureInitialized()
+{
+    if (!isInitialized) {
+        init();
+        isInitialized = true;
+    }
+}
+
 void QQmlApplicationEnginePrivate::cleanUp()
 {
     Q_Q(QQmlApplicationEngine);
@@ -81,10 +89,7 @@ void QQmlApplicationEnginePrivate::startLoad(const QUrl &url, const QByteArray &
 {
     Q_Q(QQmlApplicationEngine);
 
-    if (!isInitialized) {
-        init();
-        isInitialized = true;
-    }
+    ensureInitialized();
 
     if (url.scheme() == QLatin1String("file") || url.scheme() == QLatin1String("qrc")) {
         QFileInfo fi(QQmlFile::urlToLocalFileOrQrc(url));
@@ -101,11 +106,19 @@ void QQmlApplicationEnginePrivate::startLoad(const QUrl &url, const QByteArray &
     else
         c->loadUrl(url);
 
-    if (!c->isLoading()) {
-        finishLoad(c);
-        return;
-    }
-    QObject::connect(c, &QQmlComponent::statusChanged, q, [this, c] { this->finishLoad(c); });
+    ensureLoadingFinishes(c);
+}
+
+void QQmlApplicationEnginePrivate::startLoad(QAnyStringView uri, QAnyStringView type)
+{
+    Q_Q(QQmlApplicationEngine);
+
+    _q_loadTranslations(); //Translations must be loaded before the QML file is
+    QQmlComponent *c = new QQmlComponent(q, q);
+
+    ensureInitialized();
+    c->loadFromModule(uri, type);
+    ensureLoadingFinishes(c);
 }
 
 void QQmlApplicationEnginePrivate::finishLoad(QQmlComponent *c)
@@ -142,6 +155,16 @@ void QQmlApplicationEnginePrivate::finishLoad(QQmlComponent *c)
     c->deleteLater();
 }
 
+void QQmlApplicationEnginePrivate::ensureLoadingFinishes(QQmlComponent *c)
+{
+    Q_Q(QQmlApplicationEngine);
+    if (!c->isLoading()) {
+        finishLoad(c);
+        return;
+    }
+    QObject::connect(c, &QQmlComponent::statusChanged, q, [this, c] { this->finishLoad(c); });
+}
+
 /*!
   \class QQmlApplicationEngine
   \since 5.1
@@ -249,6 +272,18 @@ QQmlApplicationEngine::QQmlApplicationEngine(const QUrl &url, QObject *parent)
 }
 
 /*!
+  Create a new QQmlApplicationEngine and loads the QML type specified by
+  \a uri and \a typeName
+  This is provided as a convenience,  and is the same as using the empty constructor and calling
+  loadFromModule afterwards.
+*/
+QQmlApplicationEngine::QQmlApplicationEngine(QAnyStringView uri, QAnyStringView typeName, QObject *parent)
+    : QQmlApplicationEngine(parent)
+{
+    loadFromModule(uri, typeName);
+}
+
+/*!
   Create a new QQmlApplicationEngine and loads the QML file at the given
   \a filePath, which must be a local file path. If a relative path is
   given then it will be interpreted as relative to the working directory of the
@@ -302,6 +337,30 @@ void QQmlApplicationEngine::load(const QString &filePath)
 }
 
 /*!
+    Loads the QML type \a typeName from the module specified by \a uri.
+    If the type originates from a QML file located at a  remote url,
+    the type will be loaded asynchronously.
+    Listen to the \l {QQmlApplicationEngine::objectCreated()}{objectCreated}
+    signal to determine when the object tree is ready.
+
+    If an error occurs, the \l {QQmlApplicationEngine::objectCreated()}{objectCreated}
+    signal is emitted with a null pointer as parameter and error messages are printed
+    with qWarning.
+
+    \code
+    QQmlApplicationEngine engine;
+    engine.loadFromModule("QtQuick", "Rectangle");
+    \endcode
+
+    \sa QQmlComponent::loadFromModule
+ */
+void QQmlApplicationEngine::loadFromModule(QAnyStringView uri, QAnyStringView typeName)
+{
+    Q_D(QQmlApplicationEngine);
+    d->startLoad(uri, typeName);
+}
+
+/*!
    Sets the \a initialProperties with which the QML component gets initialized after
    it gets loaded.
 
diff --git a/src/qml/qml/qqmlapplicationengine.h b/src/qml/qml/qqmlapplicationengine.h
index 828629602e..afbb76dd06 100644
--- a/src/qml/qml/qqmlapplicationengine.h
+++ b/src/qml/qml/qqmlapplicationengine.h
@@ -19,6 +19,7 @@ class Q_QML_EXPORT QQmlApplicationEngine : public QQmlEngine
 public:
     QQmlApplicationEngine(QObject *parent = nullptr);
     QQmlApplicationEngine(const QUrl &url, QObject *parent = nullptr);
+    QQmlApplicationEngine(QAnyStringView uri, QAnyStringView typeName, QObject *parent = nullptr);
     QQmlApplicationEngine(const QString &filePath, QObject *parent = nullptr);
     ~QQmlApplicationEngine() override;
 
@@ -27,6 +28,7 @@ public:
 public Q_SLOTS:
     void load(const QUrl &url);
     void load(const QString &filePath);
+    void loadFromModule(QAnyStringView uri, QAnyStringView typeName);
     void setInitialProperties(const QVariantMap &initialProperties);
     void setExtraFileSelectors(const QStringList &extraFileSelectors);
     void loadData(const QByteArray &data, const QUrl &url = QUrl());
diff --git a/src/qml/qml/qqmlapplicationengine_p.h b/src/qml/qml/qqmlapplicationengine_p.h
index 7ff7a954b1..4cf21bba6d 100644
--- a/src/qml/qml/qqmlapplicationengine_p.h
+++ b/src/qml/qml/qqmlapplicationengine_p.h
@@ -30,12 +30,15 @@ class Q_QML_PRIVATE_EXPORT QQmlApplicationEnginePrivate : public QQmlEnginePriva
 public:
     QQmlApplicationEnginePrivate(QQmlEngine *e);
     ~QQmlApplicationEnginePrivate();
+    void ensureInitialized();
     void init();
     void cleanUp();
 
     void startLoad(const QUrl &url, const QByteArray &data = QByteArray(), bool dataFlag = false);
+    void startLoad(QAnyStringView uri, QAnyStringView type);
     void _q_loadTranslations();
     void finishLoad(QQmlComponent *component);
+    void ensureLoadingFinishes(QQmlComponent *component);
     QList<QObject *> objects;
     QVariantMap initialProperties;
     QStringList extraFileSelectors;
diff --git a/src/qml/qml/qqmlfileselector.cpp b/src/qml/qml/qqmlfileselector.cpp
index e13dbba819..1704e2d994 100644
--- a/src/qml/qml/qqmlfileselector.cpp
+++ b/src/qml/qml/qqmlfileselector.cpp
@@ -163,10 +163,7 @@ QQmlFileSelector* QQmlFileSelector::get(QQmlEngine* engine)
 
     if (qobject_cast<QQmlApplicationEngine *>(engine)) {
         auto *appEnginePrivate = static_cast<QQmlApplicationEnginePrivate *>(enginePrivate);
-        if (!appEnginePrivate->isInitialized) {
-            appEnginePrivate->init();
-            appEnginePrivate->isInitialized = true;
-        }
+        appEnginePrivate->ensureInitialized();
     }
 
     const QUrl nonEmptyInvalid(QLatin1String(":"));
diff --git a/tests/auto/qml/qqmlapplicationengine/tst_qqmlapplicationengine.cpp b/tests/auto/qml/qqmlapplicationengine/tst_qqmlapplicationengine.cpp
index d0f580cf5f..5774b68c32 100644
--- a/tests/auto/qml/qqmlapplicationengine/tst_qqmlapplicationengine.cpp
+++ b/tests/auto/qml/qqmlapplicationengine/tst_qqmlapplicationengine.cpp
@@ -50,12 +50,12 @@ void tst_qqmlapplicationengine::basicLoading()
 {
     int size = 0;
 
-    QQmlApplicationEngine *test = new QQmlApplicationEngine(testFileUrl("basicTest.qml"));
+    auto test = std::make_unique<QQmlApplicationEngine>(testFileUrl("basicTest.qml"));
     QCOMPARE(test->rootObjects().size(), ++size);
     QVERIFY(test->rootObjects()[size -1]);
     QVERIFY(test->rootObjects()[size -1]->property("success").toBool());
 
-    QSignalSpy objectCreated(test, SIGNAL(objectCreated(QObject*,QUrl)));
+    QSignalSpy objectCreated(test.get(), &QQmlApplicationEngine::objectCreated);
     test->load(testFileUrl("basicTest.qml"));
     QCOMPARE(objectCreated.size(), size);//one less than rootObjects().size() because we missed the first one
     QCOMPARE(test->rootObjects().size(), ++size);
@@ -69,7 +69,11 @@ void tst_qqmlapplicationengine::basicLoading()
     QVERIFY(test->rootObjects()[size -1]);
     QVERIFY(test->rootObjects()[size -1]->property("success").toBool());
 
-    delete test;
+    test->loadFromModule("QtQuick", "Rectangle");
+    QCOMPARE(objectCreated.size(), size);
+    QCOMPARE(test->rootObjects().size(), ++size);
+    QVERIFY(test->rootObjects()[size -1]);
+    QCOMPARE(test->rootObjects()[size -1]->metaObject()->className(), "QQuickRectangle");
 }
 
 // make sure we resolve a relative URL to an absolute one, otherwise things