diff options
| author | Olivier JG <olivier.de.gaalon@kdab.com> | 2016-12-16 09:57:37 -0600 |
|---|---|---|
| committer | Giuseppe D'Angelo <giuseppe.dangelo@kdab.com> | 2017-05-17 09:23:39 +0000 |
| commit | 4425d6f9b637e7404379b611cef4b22929acbe62 (patch) | |
| tree | ceaa670ee0efc6ed3a455aa18a6ec0784854629d /src/qml/doc | |
| parent | dc3015e891e903e6f701f1abc303be9f2efc2e5a (diff) | |
QML: emit messages when breaking bindings
Add a new logging category that can be used to debug issues with
unexpected binding breakages caused by assignment to previously bound
properties. If enabled, outputs a message when a binding is broken with
detailed location and property/value information.
[ChangeLog][QtQml] The QML engine can now emit informational messages
(in the "qt.qml.binding.removal" logging category) whenever a binding is
lost due to an imperative assignment. This can be used to debug issues
due to broken bindings.
Change-Id: Ie31e5a198450b6f998c1266acfc97e8f33a92e3d
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Diffstat (limited to 'src/qml/doc')
| -rw-r--r-- | src/qml/doc/src/qmllanguageref/syntax/propertybinding.qdoc | 20 |
1 files changed, 20 insertions, 0 deletions
diff --git a/src/qml/doc/src/qmllanguageref/syntax/propertybinding.qdoc b/src/qml/doc/src/qmllanguageref/syntax/propertybinding.qdoc index f28ff5082a..99426d984d 100644 --- a/src/qml/doc/src/qmllanguageref/syntax/propertybinding.qdoc +++ b/src/qml/doc/src/qmllanguageref/syntax/propertybinding.qdoc @@ -179,6 +179,26 @@ Rectangle { Now, after the space key is pressed, the rectangle's height will continue auto-updating to always be three times its width. +\section3 Debugging overwriting of bindings + +A common cause of bugs in QML applications is accidentally overwriting bindings +with static values from JavaScript statements. To help developers track down +problems of this kind, the QML engine is able to emit messages whenever a +binding is lost due to imperative assignments. + +In order to generate such messages, you need to enable the informational output +for the \c{qt.qml.binding.removal} logging category, for instance by calling: + +\code +QLoggingCategory::setFilterRules(QStringLiteral("qt.qml.binding.removal.info=true")); +\endcode + +Please refer to the QLoggingCategory documentation for more information about +enabling output from logging categories. + +Note that is perfectly reasonable in some circumstances to overwrite bindings. +Any message generated by the QML engine should be treated as a diagnostic aid, +and not necessarily as evidence of a problem without further investigation. \section2 Using \c this with Property Binding |