diff options
Diffstat (limited to 'src/qml/doc/src/qmllanguageref/syntax')
-rw-r--r-- | src/qml/doc/src/qmllanguageref/syntax/objectattributes.qdoc | 38 | ||||
-rw-r--r-- | src/qml/doc/src/qmllanguageref/syntax/propertybinding.qdoc | 20 |
2 files changed, 58 insertions, 0 deletions
diff --git a/src/qml/doc/src/qmllanguageref/syntax/objectattributes.qdoc b/src/qml/doc/src/qmllanguageref/syntax/objectattributes.qdoc index d789c67fde..207fb53ca0 100644 --- a/src/qml/doc/src/qmllanguageref/syntax/objectattributes.qdoc +++ b/src/qml/doc/src/qmllanguageref/syntax/objectattributes.qdoc @@ -50,6 +50,7 @@ The set of QML object-type attribute types is as follows: \li signal handler attributes \li method attributes \li attached properties and attached signal handler attributes +\li enumeration attributes \endlist These attributes are discussed in detail below. @@ -974,4 +975,41 @@ ListView { Now \c delegateItem.ListView.isCurrentItem correctly refers to the \c isCurrentItem attached property of the delegate. +\section2 Enumeration Attributes + +Enumerations provide a fixed set of named choices. They can be declared in QML using the \c enum keyword: + +\qml +// MyText.qml +Text { + enum TextType { + Normal, + Heading + } +} +\endqml + +As shown above, enumeration types (e.g. \c TextType) and values (e.g. \c Normal) must begin with an uppercase letter. + +Values are referred to via \c {<Type>.<EnumerationType>.<Value>} or \c {<Type>.<Value>}. + +\qml +// MyText.qml +Text { + enum TextType { + Normal, + Heading + } + + property int textType: MyText.TextType.Normal + + font.bold: textType == MyText.TextType.Heading + font.pixelSize: textType == MyText.TextType.Heading ? 24 : 12 +} +\endqml + +More information on enumeration usage in QML can be found in the \l {QML Basic Types} \l enumeration documentation. + +The ability to declare enumerations in QML was introduced in Qt 5.10. + */ diff --git a/src/qml/doc/src/qmllanguageref/syntax/propertybinding.qdoc b/src/qml/doc/src/qmllanguageref/syntax/propertybinding.qdoc index b506de471f..a5ad6af4a2 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 |