Add delayed property to Binding.

Provide a way to avoid potentially expensive or unexpected intermediate
values.

[ChangeLog][Binding] Add delayed property to Binding as a way to avoid potentially expensive or unexpected intermediate values.

Change-Id: I6aaca570859cc1344eeb9c9f19f32660e8c0b4e0
Reviewed-by: Robin Burchell <robin.burchell@viroteck.net>

4 files changed, 51 insertions, 3 deletions

diff --git a/tests/auto/qml/qqmlbinding/data/delayed.qml b/tests/auto/qml/qqmlbinding/data/delayed.qml
new file mode 100644
index 0000000000..6f8281cc33
--- /dev/null
+++ b/tests/auto/qml/qqmlbinding/data/delayed.qml
@@ -0,0 +1,26 @@
+import QtQuick 2.8
+
+Item {
+    width: 400
+    height: 400
+
+    property int changeCount: 0
+
+    property string text1
+    property string text2
+
+    function updateText() {
+        text1 = "Hello"
+        text2 = "World"
+    }
+
+    Text {
+        anchors.centerIn: parent
+        Binding on text {
+            value: text1 + " " + text2
+            delayed: true
+        }
+        onTextChanged: ++changeCount
+    }
+}
+
diff --git a/tests/auto/qml/qqmlbinding/tst_qqmlbinding.cpp b/tests/auto/qml/qqmlbinding/tst_qqmlbinding.cpp
index 3e8dfbdb12..6f1d82eca5 100644
--- a/tests/auto/qml/qqmlbinding/tst_qqmlbinding.cpp
+++ b/tests/auto/qml/qqmlbinding/tst_qqmlbinding.cpp
@@ -49,6 +49,7 @@ private slots:
     void warningOnReadOnlyProperty();
     void disabledOnUnknownProperty();
     void disabledOnReadonlyProperty();
+    void delayed();
 
 private:
     QQmlEngine engine;
@@ -281,6 +282,27 @@ void tst_qqmlbinding::disabledOnReadonlyProperty()
     QCOMPARE(messageHandler.messages().count(), 0);
 }
 
+void tst_qqmlbinding::delayed()
+{
+    QQmlEngine engine;
+    QQmlComponent c(&engine, testFileUrl("delayed.qml"));
+    QQuickItem *item = qobject_cast<QQuickItem*>(c.create());
+
+    QVERIFY(item != 0);
+    // update on creation
+    QCOMPARE(item->property("changeCount").toInt(), 1);
+
+    QMetaObject::invokeMethod(item, "updateText");
+    // doesn't update immediately
+    QCOMPARE(item->property("changeCount").toInt(), 1);
+
+    QCoreApplication::processEvents();
+    // only updates once (non-delayed would update twice)
+    QCOMPARE(item->property("changeCount").toInt(), 2);
+
+    delete item;
+}
+
 QTEST_MAIN(tst_qqmlbinding)
 
 #include "tst_qqmlbinding.moc"
diff --git a/tests/auto/qml/qqmlengine/data/qtqmlModule.4.qml b/tests/auto/qml/qqmlengine/data/qtqmlModule.4.qml
index 9b9b7922da..94ee46ddf0 100644
--- a/tests/auto/qml/qqmlengine/data/qtqmlModule.4.qml
+++ b/tests/auto/qml/qqmlengine/data/qtqmlModule.4.qml
@@ -1,4 +1,4 @@
-import QtQml 2.5
+import QtQml 2.50
 
 QtObject {
 }
diff --git a/tests/auto/qml/qqmlengine/tst_qqmlengine.cpp b/tests/auto/qml/qqmlengine/tst_qqmlengine.cpp
index 3208745c5c..3af1cf46b3 100644
--- a/tests/auto/qml/qqmlengine/tst_qqmlengine.cpp
+++ b/tests/auto/qml/qqmlengine/tst_qqmlengine.cpp
@@ -615,9 +615,9 @@ void tst_qqmlengine::qtqmlModule_data()
             << QString(testFileUrl("qtqmlModule.3.qml").toString() + QLatin1String(":1 module \"QtQml\" version 1.0 is not installed\n"))
             << QStringList();
 
-    QTest::newRow("import QtQml of incorrect version (2.5)")
+    QTest::newRow("import QtQml of incorrect version (2.50)")
             << testFileUrl("qtqmlModule.4.qml")
-            << QString(testFileUrl("qtqmlModule.4.qml").toString() + QLatin1String(":1 module \"QtQml\" version 2.5 is not installed\n"))
+            << QString(testFileUrl("qtqmlModule.4.qml").toString() + QLatin1String(":1 module \"QtQml\" version 2.50 is not installed\n"))
             << QStringList();
 
     QTest::newRow("QtQml 2.0 module provides Component, QtObject, Connections, Binding and Timer")