From ed7a6358e35f5fdaf7468371a8b29aa6a3ef0fe7 Mon Sep 17 00:00:00 2001
From: Mitch Curtis <mitch.curtis@theqtcompany.com>
Date: Thu, 16 Oct 2014 11:06:32 +0200
Subject: [PATCH] Add note to QQuickItem docs about directly setting properties
in C++.
It's not obvious that calling setPosition() directly, for example,
won't trigger animations defined in behaviors that react to that
item's x and y properties changing, because a quick glance at the
code shows that they have almost identical code paths and both
emit geometryChanged().
Change-Id: Ic7f7019b1bbba24732569c0de777ee02d79c1d3b
Reviewed-by: Gunnar Sletta <gunnar@sletta.org>
---
src/quick/items/qquickitem.cpp | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/src/quick/items/qquickitem.cpp b/src/quick/items/qquickitem.cpp
index a1376682af..0fb8d0e2f8 100644
--- a/src/quick/items/qquickitem.cpp
+++ b/src/quick/items/qquickitem.cpp
@@ -1749,6 +1749,19 @@ void QQuickItemPrivate::updateSubFocusItem(QQuickItem *scope, bool focus)
surface. Using scene graph API directly is always significantly
faster.
+ \section1 Behavior Animations
+
+ If your Item uses the \l Behavior type to define animations for property
+ changes, you should always use either QObject::setProperty(),
+ QQmlProperty(), or QMetaProperty::write() when you need to modify those
+ properties from C++. This ensures that the QML engine knows about the
+ property change. Otherwise, the engine won't be able to carry out your
+ requested animation. For example, if you call \l setPosition() directly,
+ any behavior that reacts to changes in the x or y properties will not take
+ effect, as you are bypassing Qt's meta-object system. Note that these
+ functions incur a slight performance penalty. For more details, see
+ \l {Accessing Members of a QML Object Type from C++}.
+
\sa QQuickWindow, QQuickPaintedItem
*/
--
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