QQuickLoader: store status

This allows us to emit the change signal only when the status has
actually changed. Due to alignment restrictions, this does not even
change the size of the class.

Fixes: QTBUG-82002
Change-Id: I2192bf80e72b92108046780811c3acdab39af518
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

4 files changed, 91 insertions, 39 deletions

diff --git a/src/quick/items/qquickloader.cpp b/src/quick/items/qquickloader.cpp
index b389e7a11b..8c15b60712 100644
--- a/src/quick/items/qquickloader.cpp
+++ b/src/quick/items/qquickloader.cpp
@@ -55,7 +55,7 @@ static const QQuickItemPrivate::ChangeTypes watchedChanges
 
 QQuickLoaderPrivate::QQuickLoaderPrivate()
     : item(nullptr), object(nullptr), itemContext(nullptr), incubator(nullptr), updatingSize(false),
-      active(true), loadingFromSource(false), asynchronous(false)
+      active(true), loadingFromSource(false), asynchronous(false), status(computeStatus())
 {
 }
 
@@ -378,7 +378,7 @@ void QQuickLoader::setActive(bool newVal)
             d->object = nullptr;
             emit itemChanged();
         }
-        emit statusChanged();
+        d->updateStatus();
     }
     emit activeChanged();
 }
@@ -431,7 +431,7 @@ void QQuickLoader::loadFromSource()
     Q_D(QQuickLoader);
     if (d->source.isEmpty()) {
         emit sourceChanged();
-        emit statusChanged();
+        d->updateStatus();
         emit progressChanged();
         emit itemChanged();
         return;
@@ -502,7 +502,7 @@ void QQuickLoader::loadFromSourceComponent()
     Q_D(QQuickLoader);
     if (!d->component) {
         emit sourceComponentChanged();
-        emit statusChanged();
+        d->updateStatus();
         emit progressChanged();
         emit itemChanged();
         return;
@@ -618,7 +618,7 @@ void QQuickLoaderPrivate::load()
                 q, SLOT(_q_sourceLoaded()));
         QObject::connect(component, SIGNAL(progressChanged(qreal)),
                 q, SIGNAL(progressChanged()));
-        emit q->statusChanged();
+        updateStatus();
         emit q->progressChanged();
         if (loadingFromSource)
             emit q->sourceChanged();
@@ -705,7 +705,7 @@ void QQuickLoaderPrivate::incubatorStateChanged(QQmlIncubator::Status status)
         emit q->sourceChanged();
     else
         emit q->sourceComponentChanged();
-    emit q->statusChanged();
+    updateStatus();
     emit q->progressChanged();
     if (status == QQmlIncubator::Ready)
         emit q->loaded();
@@ -722,7 +722,7 @@ void QQuickLoaderPrivate::_q_sourceLoaded()
             emit q->sourceChanged();
         else
             emit q->sourceComponentChanged();
-        emit q->statusChanged();
+        updateStatus();
         emit q->progressChanged();
         emit q->itemChanged(); //Like clearing source, emit itemChanged even if previous item was also null
         disposeInitialPropertyValues(); // cleanup
@@ -740,7 +740,7 @@ void QQuickLoaderPrivate::_q_sourceLoaded()
     component->create(*incubator, itemContext);
 
     if (incubator && incubator->status() == QQmlIncubator::Loading)
-        emit q->statusChanged();
+        updateStatus();
 }
 
 /*!
@@ -787,37 +787,7 @@ QQuickLoader::Status QQuickLoader::status() const
 {
     Q_D(const QQuickLoader);
 
-    if (!d->active)
-        return Null;
-
-    if (d->component) {
-        switch (d->component->status()) {
-        case QQmlComponent::Loading:
-            return Loading;
-        case QQmlComponent::Error:
-            return Error;
-        case QQmlComponent::Null:
-            return Null;
-        default:
-            break;
-        }
-    }
-
-    if (d->incubator) {
-        switch (d->incubator->status()) {
-        case QQmlIncubator::Loading:
-            return Loading;
-        case QQmlIncubator::Error:
-            return Error;
-        default:
-            break;
-        }
-    }
-
-    if (d->object)
-        return Ready;
-
-    return d->source.isEmpty() ? Null : Error;
+    return static_cast<Status>(d->status);
 }
 
 void QQuickLoader::componentComplete()
@@ -1018,6 +988,51 @@ QV4::ReturnedValue QQuickLoaderPrivate::extractInitialPropertyValues(QQmlV4Funct
     return valuemap->asReturnedValue();
 }
 
+QQuickLoader::Status QQuickLoaderPrivate::computeStatus() const
+{
+    if (!active)
+        return QQuickLoader::Status::Null;
+
+    if (component) {
+        switch (component->status()) {
+        case QQmlComponent::Loading:
+            return QQuickLoader::Status::Loading;
+        case QQmlComponent::Error:
+            return QQuickLoader::Status::Error;
+        case QQmlComponent::Null:
+            return QQuickLoader::Status::Null;
+        default:
+            break;
+        }
+    }
+
+    if (incubator) {
+        switch (incubator->status()) {
+        case QQmlIncubator::Loading:
+            return QQuickLoader::Status::Loading;
+        case QQmlIncubator::Error:
+            return QQuickLoader::Status::Error;
+        default:
+            break;
+        }
+    }
+
+    if (object)
+        return QQuickLoader::Status::Ready;
+
+    return source.isEmpty() ? QQuickLoader::Status::Null : QQuickLoader::Status::Error;
+}
+
+void QQuickLoaderPrivate::updateStatus()
+{
+    Q_Q(QQuickLoader);
+    auto newStatus = computeStatus();
+    if (status != newStatus) {
+        status = newStatus;
+        emit q->statusChanged();
+    }
+}
+
 #include <moc_qquickloader_p.cpp>
 
 QT_END_NAMESPACE
diff --git a/src/quick/items/qquickloader_p_p.h b/src/quick/items/qquickloader_p_p.h
index 349b5c6c06..39d50280c5 100644
--- a/src/quick/items/qquickloader_p_p.h
+++ b/src/quick/items/qquickloader_p_p.h
@@ -96,6 +96,8 @@ public:
     void disposeInitialPropertyValues();
     static QUrl resolveSourceUrl(QQmlV4Function *args);
     QV4::ReturnedValue extractInitialPropertyValues(QQmlV4Function *args, QObject *loader, bool *error);
+    QQuickLoader::Status computeStatus() const;
+    void updateStatus();
 
     qreal getImplicitWidth() const override;
     qreal getImplicitHeight() const override;
@@ -112,6 +114,11 @@ public:
     bool active : 1;
     bool loadingFromSource : 1;
     bool asynchronous : 1;
+    // We need to use char instead of QQuickLoader::Status
+    // as otherwise the size of the class would increase
+    // on 32-bit systems, as sizeof(Status) == sizeof(int)
+    // and sizeof(int) > remaining padding on 32 bit
+    char status;
 
     void _q_sourceLoaded();
     void _q_updateSize(bool loaderGeometryChanged = true);
diff --git a/tests/auto/quick/qquickloader/data/statusChanged.qml b/tests/auto/quick/qquickloader/data/statusChanged.qml
new file mode 100644
index 0000000000..fe46bc7b24
--- /dev/null
+++ b/tests/auto/quick/qquickloader/data/statusChanged.qml
@@ -0,0 +1,16 @@
+import QtQuick 2.12
+import QtQuick.Window 2.12
+
+Window {
+    id: root
+    property int statusChangedCounter: 0
+    property alias status: loader.status
+    visible: true; width: 640; height: 480
+    Loader {
+        id: loader
+        anchors.fill: parent
+        asynchronous: true
+        source: "./RedRect.qml"
+        onStatusChanged: root.statusChangedCounter++
+    }
+}
diff --git a/tests/auto/quick/qquickloader/tst_qquickloader.cpp b/tests/auto/quick/qquickloader/tst_qquickloader.cpp
index d0a1a8a45b..7bd6f9466a 100644
--- a/tests/auto/quick/qquickloader/tst_qquickloader.cpp
+++ b/tests/auto/quick/qquickloader/tst_qquickloader.cpp
@@ -39,6 +39,7 @@
 #include "testhttpserver.h"
 #include "../../shared/util.h"
 #include "../shared/geometrytestutil.h"
+#include <QQmlApplicationEngine>
 
 Q_LOGGING_CATEGORY(lcTests, "qt.quick.tests")
 
@@ -128,6 +129,7 @@ private slots:
     void rootContext();
     void sourceURLKeepComponent();
 
+    void statusChangeOnlyEmittedOnce();
 };
 
 Q_DECLARE_METATYPE(QList<QQmlError>)
@@ -1446,6 +1448,18 @@ void tst_QQuickLoader::sourceURLKeepComponent()
 
 }
 
+// QTBUG-82002
+void tst_QQuickLoader::statusChangeOnlyEmittedOnce()
+{
+    QQmlApplicationEngine engine;
+    auto url = testFileUrl("statusChanged.qml");
+    engine.load(url);
+    auto root = engine.rootObjects().at(0);
+    QVERIFY(root);
+    QTRY_COMPARE(QQuickLoader::Status(root->property("status").toInt()), QQuickLoader::Ready);
+    QCOMPARE(root->property("statusChangedCounter").toInt(), 2); // 1xLoading + 1xReady*/
+}
+
 QTEST_MAIN(tst_QQuickLoader)
 
 #include "tst_qquickloader.moc"