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Diffstat (limited to 'doc/src/declarative/propertybinding.qdoc')
| -rw-r--r-- | doc/src/declarative/propertybinding.qdoc | 30 |
1 files changed, 18 insertions, 12 deletions
diff --git a/doc/src/declarative/propertybinding.qdoc b/doc/src/declarative/propertybinding.qdoc index 3bf85de..92cf874 100644 --- a/doc/src/declarative/propertybinding.qdoc +++ b/doc/src/declarative/propertybinding.qdoc @@ -27,15 +27,21 @@ /*! \page propertybinding.html +\ingroup qml-features +\contentspage QML Features +\previouspage QML Features +\nextpage Using QML Positioner and Repeater Items \title Property Binding + +\section1 Introduction Property binding is a declarative way of specifying the value of a property. Binding allows a property's value to be expressed as an JavaScript expression that defines the value relative -to other property values or data accessible in the application. The property value is +to other property values or data accessible in the application. The property value is automatically kept up to date if the other properties or data values change. -Property bindings are created implicitly in QML whenever a property is assigned an JavaScript -expression. The following QML uses two property bindings to connect the size of the rectangle +Property bindings are created implicitly in QML whenever a property is assigned a JavaScript +expression. The following QML code uses two property bindings to connect the size of the rectangle to that of \c otherItem. \code @@ -45,9 +51,9 @@ Rectangle { } \endcode -QML extends a standards compliant JavaScript engine, so any valid JavaScript expression can be +QML extends a standards compliant JavaScript engine, so any valid JavaScript expression can be used as a property binding. Bindings can access object properties, make function calls and even -use builtin JavaScript objects like \e {Date} and \e {Math}. Assigning a constant value to a +use built-in JavaScript objects like \c {Date} and \c {Math}. Assigning a constant value to a property can even be thought of as a binding - after all, a constant is a valid JavaScript expression! Here are some examples of more complex bindings: @@ -71,10 +77,10 @@ function. \section1 Changing Bindings -The \l PropertyChanges element can be used within a state change to modify the bindings on -properties. +The \l PropertyChanges element can be used within a state change to modify the bindings on +properties. -This example modifies the \l Rectangle's width property binding to be \c {otherItem.height} +This example modifies the \l Rectangle's width property binding to be \c {otherItem.height} when in the "square" state. When it returns to its default state, width's original property binding will have been restored. @@ -97,7 +103,7 @@ Rectangle { \section1 Effects of Property Assignment in JavaScript -Assigning a property value from JavaScript does \e not create a property binding. +Assigning a property value from JavaScript does \i not create a property binding. For example: \code @@ -110,10 +116,10 @@ Rectangle { \endcode Instead of creating a property binding, this simply sets the \c width of the \l Rectangle -to the value of \c other.width at the time the JavaScript code is invoked. See +to the value of \c other.width at the time the JavaScript code is invoked. See \l {Property Assignment vs Property Binding} for more details. -Also note that assigning a value to a property that is currently bound will remove the binding. +Also note that assigning a value to a property that is currently bound will remove the previous binding. A property can only have one value at a time, and if any code explicitly sets this value, the binding is removed. The \l Rectangle in the example below will have a width of 13, regardless of the \c otherItem's width. @@ -135,7 +141,7 @@ although it is possible to set up a \l Binding object (shown below). \section1 Binding Element The implicit binding syntax shown previously is easy to use and works perfectly for most uses -of bindings. In some advanced cases, it is necessary to create bindings explicitly using the +of bindings. In some advanced cases, it is necessary to create bindings explicitly using the \l Binding element. For example, to bind a property exposed from C++ (\c system.brightness) to a value |