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/****************************************************************************
**
** Copyright (C) 2013 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
** Commercial License Usage
** Licensees holding valid commercial Qt licenses may use this file in
** accordance with the commercial license agreement provided with the
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**
** GNU Free Documentation License Usage
** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: http://www.gnu.org/copyleft/fdl.html.
** $QT_END_LICENSE$
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****************************************************************************/
/*!
\example tools/customtypesending
\title Custom Type Sending Example
The Custom Type Sending example shows how to use a custom type with signals
and slots.
\image customtypesending-example.png
\section1 Overview
In the \l{Custom Type Example}, we showed how to integrate custom types
with the meta-object system, enabling them to be stored in QVariant
objects, written out in debugging information and used in signal-slot
communication.
In this example, we demonstrate that the preparations made to the
\c Message class and its declaration with Q_DECLARE_METATYPE() enable it
to be used with direct signal-slot connections. We do this by creating
a \c Window class containing signals and slots whose signatures include
\c Message arguments.
\section1 The Window and Message Class Definitions
We define a simple \c Window class with a signal and public slot that
allow a \c Message object to be sent via a signal-slot connection:
\snippet examples/tools/customtypesending/window.h Window class definition
The window will contain a text editor to show the contents of a message
and a push button that the user can click to send a message. To facilitate
this, we also define the \c sendMessage() slot. We also keep a \c Message
instance in the \c thisMessage private variable which holds the actual
message to be sent.
The \c Message class is defined in the following way:
\snippet examples/tools/customtypesending/message.h custom type definition
The type is declared to the meta-type system with the Q_DECLARE_METATYPE()
macro:
\snippet examples/tools/customtypesending/message.h custom type meta-type declaration
This will make the type available for use in direct signal-slot connections.
\section1 The Window Class Implementation
The \c Window constructor sets up a user interface containing a text
editor and a push button.
\snippet examples/tools/customtypesending/window.cpp Window constructor
The button's \l{QPushButton::}{clicked()} signal is connected to the
window's \c{sendMessage()} slot, which emits the \c{messageSent(Message)}
signal with the \c Message held by the \c thisMessage variable:
\snippet examples/tools/customtypesending/window.cpp sending a message
We implement a slot to allow the message to be received, and this also
lets us set the message in the window programatically:
\snippet examples/tools/customtypesending/window.cpp receiving a message
In this function, we simply assign the new message to \c thisMessage
and update the text in the editor.
\section1 Making the Connection
In the example's \c{main()} function, we perform the connection between
two instances of the \c Window class:
\snippet examples/tools/customtypesending/main.cpp main function
We set the message for the first window and connect the
\c{messageSent(Message)} signal from each window to the other's
\c{setMessage(Message)} slot. Since the signals and slots mechanism is only
concerned with the type, we can simplify the signatures of both the
signal and slot when we make the connection.
When the user clicks on the \uicontrol{Send message} button in either window,
the message shown will be emitted in a signal that the other window will
receive and display.
\section1 Further Reading
Although the custom \c Message type can be used with direct signals and
slots, an additional registration step needs to be performed if you want
to use it with queued signal-slot connections. See the
\l{Queued Custom Type Example} for details.
More information on using custom types with Qt can be found in the
\l{Creating Custom Qt Types} document.
*/
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