Provide API to access singletons associated with a QQmlEngine

This patch adds allows C++ code to retrieve the instance of a registered
singleton type. Until now this required a deturn via QML expression.

Two methods are added to QQmlEngine: A generic one that encapsulates all
singleton objects in a QJSValue and a template function for QObject-derived
singleton types.

An additional convenience function is added to query the QML type id.  This
function may also be used for other purposes in the future.

[ChangeLog][QtQml][QQmlEngine] Added API to access singletons associated with
a QQmlEngine.

Task-number: QTBUG-39970
Change-Id: I67c132ede35f80b9aaf1c5e5456715cf4f1b0848
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

1 files changed, 22 insertions, 0 deletions

diff --git a/tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp b/tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp
index 39f973f3fd..f3569c2efe 100644
--- a/tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp
+++ b/tests/auto/qml/qqmllanguage/tst_qqmllanguage.cpp
@@ -290,6 +290,8 @@ private slots:
 
     void valueTypeGroupPropertiesInBehavior();
 
+    void retrieveQmlTypeId();
+
 private:
     QQmlEngine engine;
     QStringList defaultImportPathList;
@@ -4956,6 +4958,26 @@ void tst_qqmllanguage::valueTypeGroupPropertiesInBehavior()
     QCOMPARE(animation->property("easing").value<QEasingCurve>().type(), QEasingCurve::InOutQuad);
 }
 
+void tst_qqmllanguage::retrieveQmlTypeId()
+{
+    // Register in reverse order to provoke wrong minor version matching.
+    int id2 = qmlRegisterType<QObject>("Test", 2, 3, "SomeTestType");
+    int id1 = qmlRegisterType<QObject>("Test", 2, 1, "SomeTestType");
+    QCOMPARE(qmlTypeId("Test", 2, 1, "SomeTestType"), id1);
+    QCOMPARE(qmlTypeId("Test", 2, 2, "SomeTestType"), id1);
+    QCOMPARE(qmlTypeId("Test", 2, 3, "SomeTestType"), id2);
+
+    // Error cases
+    QCOMPARE(qmlTypeId("Test", 2, 0, "SomeTestType"), -1);
+    QCOMPARE(qmlTypeId("Test", 2, 3, "DoesNotExist"), -1);
+    QCOMPARE(qmlTypeId("DoesNotExist", 2, 3, "SomeTestType"), -1);
+
+    // Must also work for other types (defined in testtpes.cpp)
+    QVERIFY(qmlTypeId("Test", 1, 0, "MyExtendedUncreateableBaseClass") >= 0);
+    QVERIFY(qmlTypeId("Test", 1, 0, "MyUncreateableBaseClass") >= 0);
+    QVERIFY(qmlTypeId("Test", 1, 0, "MyTypeObjectSingleton") >= 0);
+}
+
 QTEST_MAIN(tst_qqmllanguage)
 
 #include "tst_qqmllanguage.moc"