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authorAaron Kennedy <aaron.kennedy@nokia.com>2010-02-23 01:08:37 (GMT)
committerAaron Kennedy <aaron.kennedy@nokia.com>2010-02-23 01:54:04 (GMT)
commitce78e4124d57a3c517e6de88696a09ad399c703f (patch)
treee93cb73254f8c5e924fb0c7bb15d5e4d64ad1234 /doc
parent27f35a9cb588ad1dd595fafedc27e5a216bebf48 (diff)
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Add documentation on QMLs memory management assumptions
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-rw-r--r--doc/src/declarative/extending.qdoc31
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diff --git a/doc/src/declarative/extending.qdoc b/doc/src/declarative/extending.qdoc
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@@ -375,6 +375,37 @@ object will only be returned if it has previously been created.
\l {Extending QML - Attached Properties Example} shows the complete code used to
implement the rsvp attached property.
+\section1 Memory Management and QVariant types
+
+It is an elements responsibility to ensure that it does not access or return
+pointers to invalid objects. QML makes the following guarentees:
+
+\list
+\o An object assigned to an QObject (or QObject-derived) pointer property will be
+valid at the time of assignment.
+
+Following assignment, it is the responsibility of the class to subsequently guard
+this pointer, either through a class specific method or the generic QPointer class.
+
+\o An object assigned to a QVariant will be valid at the time of assignment.
+
+When assigning an object to a QVariant property, QML will always use a QMetaType::QObjectStar
+typed QVariant. It is the responsibility of the class to guard the pointer. A
+general rule when writing a class that uses QVariant properties is to check the
+type of the QVariant when it is set and if the type is not handled by your class,
+reset it to an invalid variant.
+
+\o An object assigned to a QObject (or QObject-derived) list property will be
+valid at the time of assignment.
+
+Following assignment, it is the responsibility of the class to subsequently guard
+this pointer, either through a class specific method or the generic QPointer class.
+\endlist
+
+Elements should assume that any QML assigned object can be deleted at any time, and
+respond accordingly. If documented as such an element need not continue to work in
+this situation, but it must not crash.
+
\section1 Signal Support
\snippet examples/declarative/extending/signal/example.qml 0