diff options
Diffstat (limited to 'doc/src/declarative/qmlevents.qdoc')
-rw-r--r-- | doc/src/declarative/qmlevents.qdoc | 110 |
1 files changed, 104 insertions, 6 deletions
diff --git a/doc/src/declarative/qmlevents.qdoc b/doc/src/declarative/qmlevents.qdoc index 3c1c8df..8c2147a 100644 --- a/doc/src/declarative/qmlevents.qdoc +++ b/doc/src/declarative/qmlevents.qdoc @@ -1,6 +1,10 @@ /**************************************************************************** ** +<<<<<<< HEAD +** Copyright (C) 2011 Nokia Corporation and/or its subsidiary(-ies). +======= ** Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies). +>>>>>>> d7a91cfe8683309883694fbbf508e5fc42d44165 ** All rights reserved. ** Contact: Nokia Corporation (qt-info@nokia.com) ** @@ -26,12 +30,106 @@ ****************************************************************************/ /*! - \page qmlevents.html - \ingroup qml-features - \contentspage QML Features - \previouspage {Integrating QML Code with Existing Qt UI Code} - \nextpage {Dynamic Object Management in QML}{Dynamic Object Management} +\page qmlevents.html +\ingroup qml-features +\contentspage QML Features +\previouspage {Integrating QML Code with Existing Qt UI Code} +\nextpage {Dynamic Object Management in QML}{Dynamic Object Management} - \title QML Signal and Handler Event System +\title QML Signal and Handler Event System + +\section1 Overview, structural information + +QML utilizes Qt's \l{The Meta-Object System}{meta-object} and +\l{Signals & Slots}{signals} systems. Signals and slots created using Qt in C++ +are inheritely valid in QML. + +\keyword qml-signals-and-handlers +\section1 Signals and Handlers + +Signals provide a way to notify other objects when an event has occurred. For +example, the MouseArea \c clicked signal notifies other objects that the mouse +has been clicked within the area. + +The syntax for defining a new signal is: + +\qml +signal <name>[([<type> <parameter name>[, ...]])] +\endqml + +Attempting to declare two signals or methods with the same name in the same type +block is an error. However, a new signal may reuse the name of an existing +signal on the type. (This should be done with caution, as the existing signal +may be hidden and become inaccessible.) + +Here are various examples of signal declarations: +\snippet doc/src/snippets/declarative/events.qml parent begin +\snippet doc/src/snippets/declarative/events.qml signal declaration +\snippet doc/src/snippets/declarative/events.qml parent end + +If the signal has no parameters, the "\c{()}" brackets are optional. If +parameters are used, the parameter types must be declared, as for the \c string +and \c variant arguments of the \c perform signal. + +Adding a signal to an item automatically adds a \e{signal handler} as well. The +signal hander is named \c on<SignalName>, with the first letter of the signal in +uppercase. The previous signals have the following signal handlers: +\snippet doc/src/snippets/declarative/events.qml signal handler declaration + +Further, each QML properties have a \c{<property_name>Changed} signal and its +corresponding \c{on<property_name>Changed} signal handler. As a result, property +changes may notify other components for any changes. +\snippet doc/src/snippets/declarative/events.qml automatic signals + +To emit a signal, invoke it as a method. The signal handler binding is similar +to a property binding and it is invoked when the signal is emitted. Use the +defined argument names to access the respective arguments. +\snippet doc/src/snippets/declarative/events.qml signal emit +Note that the \c Component.onCompleted is an +\l{attached-signalhandlers}{attached signal handler}; it is invoked when the +\l Component initialization is complete. + +\keyword qml-connect-signals-to-method +\section2 Connecting Signals to Methods and Signals + +Signal objects have a \c connect() method to a connect a signal either to a +method or another signal. When a signal is connected to a method, the method is +automatically invoked whenever the signal is emitted. (In Qt terminology, the +method is a \e slot that is connected to the \e signal; all methods defined in +QML are created as \l{Signals & Slots}{Qt slots}.) This enables a signal +to be received by a method instead of a \l {Signal Handlers}{signal handler}. + +\snippet doc/src/snippets/declarative/events.qml connect method +The \c {connect()} method is appropriate when connecting a JavaScript method, +such as the \c {callee}'s\c answer method, to QML signals. + +The corresponding \c disconnect() method is for removing connected +signals. The following code removes the connection created in \c application.qml above: +\snippet doc/src/snippets/declarative/events.qml disconnect method + +\section3 Signal to Signal Connect + +By connecting signals to other signals, the \c connect() method can form different +signal chains. +\snippet doc/src/snippets/declarative/events.qml parent begin +\snippet doc/src/snippets/declarative/events.qml forward signal +\snippet doc/src/snippets/declarative/events.qml parent end + +Whenever the \l MouseArea \c clicked signal is emitted, the \c widgetClicked +signal will automatically be emitted as well. + +\code +output: + MouseArea clicked + Widget clicked +\endcode + +\section1 C++ additions + +Because QML uses Qt, a signal defined in C++ also works as a QML signal. The +signal may be emitted in QML code or called as a method. In addition, the QML +runtime automatically creates signal handlers for the C++ signals. For more +signal control, the \c connect() method and the \l Connect element may connect a +C++ to another signal or method. */ |