diff options
Diffstat (limited to 'examples/corelib/tools/doc/src')
| -rw-r--r-- | examples/corelib/tools/doc/src/contiguouscache.qdoc | 83 | ||||
| -rw-r--r-- | examples/corelib/tools/doc/src/customtype.qdoc | 143 |
2 files changed, 226 insertions, 0 deletions
diff --git a/examples/corelib/tools/doc/src/contiguouscache.qdoc b/examples/corelib/tools/doc/src/contiguouscache.qdoc new file mode 100644 index 0000000000..e88b2629b8 --- /dev/null +++ b/examples/corelib/tools/doc/src/contiguouscache.qdoc @@ -0,0 +1,83 @@ +/**************************************************************************** +** +** 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 +** Software or, alternatively, in accordance with the terms contained in +** a written agreement between you and Digia. For licensing terms and +** conditions see http://qt.digia.com/licensing. For further information +** use the contact form at http://qt.digia.com/contact-us. +** +** 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. +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \example tools/contiguouscache + \title Contiguous Cache Example + + \brief The Contiguous Cache example shows how to use QContiguousCache to manage memory usage for + very large models. In some environments memory is limited and, even when it + isn't, users still dislike an application using excessive memory. + Using QContiguousCache to manage a list, rather than loading + the entire list into memory, allows the application to limit the amount + of memory it uses, regardless of the size of the data set it accesses + + The simplest way to use QContiguousCache is to cache as items are requested. When + a view requests an item at row N it is also likely to ask for items at rows near + to N. + + \snippet tools/contiguouscache/randomlistmodel.cpp 0 + + After getting the row, the class determines if the row is in the bounds + of the contiguous cache's current range. It would have been equally valid to + simply have the following code instead. + + \code + while (row > m_rows.lastIndex()) + m_rows.append(fetchWord(m_rows.lastIndex()+1); + while (row < m_rows.firstIndex()) + m_rows.prepend(fetchWord(m_rows.firstIndex()-1); + \endcode + + However a list will often jump rows if the scroll bar is used directly, resulting in + the code above causing every row between the old and new rows to be fetched. + + Using QContiguousCache::lastIndex() and QContiguousCache::firstIndex() allows + the example to determine what part of the list the cache is currently caching. + These values don't represent the indexes into the cache's own memory, but rather + a virtual infinite array that the cache represents. + + By using QContiguousCache::append() and QContiguousCache::prepend() the code ensures + that items that may be still on the screen are not lost when the requested row + has not moved far from the current cache range. QContiguousCache::insert() can + potentially remove more than one item from the cache as QContiguousCache does not + allow for gaps. If your cache needs to quickly jump back and forth between + rows with significant gaps between them consider using QCache instead. + + And thats it. A perfectly reasonable cache, using minimal memory for a very large + list. In this case the accessor for getting the words into the cache + generates random information rather than fixed information. This allows you + to see how the cache range is kept for a local number of rows when running the + example. + + \snippet tools/contiguouscache/randomlistmodel.cpp 1 + + It is also worth considering pre-fetching items into the cache outside of the + application's paint routine. This can be done either with a separate thread + or using a QTimer to incrementally expand the range of the cache prior to + rows being requested out of the current cache range. +*/ diff --git a/examples/corelib/tools/doc/src/customtype.qdoc b/examples/corelib/tools/doc/src/customtype.qdoc new file mode 100644 index 0000000000..f03fafec30 --- /dev/null +++ b/examples/corelib/tools/doc/src/customtype.qdoc @@ -0,0 +1,143 @@ +/**************************************************************************** +** +** 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 +** Software or, alternatively, in accordance with the terms contained in +** a written agreement between you and Digia. For licensing terms and +** conditions see http://qt.digia.com/licensing. For further information +** use the contact form at http://qt.digia.com/contact-us. +** +** 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. +** $QT_END_LICENSE$ +** +****************************************************************************/ + +/*! + \example tools/customtype + \title Custom Type Example + + \brief The Custom Type example shows how to integrate a custom type into Qt's + meta-object system. + + Contents: + + \tableofcontents + + \section1 Overview + + Qt provides a range of standard value types that are used to provide + rich and meaningful APIs. These types are integrated with the meta-object + system, enabling them to be stored in QVariant objects, written out in + debugging information and sent between components in signal-slot + communication. + + Custom types can also be integrated with the meta-object system as long as + they are written to conform to some simple guidelines. In this example, we + introduce a simple \c Message class, we describe how we make it work with + QVariant, and we show how it can be extended to generate a printable + representation of itself for use in debugging output. + + \section1 The Message Class Definition + + The \c Message class is a simple value class that contains two pieces + of information (a QString and a QStringList), each of which can be read + using trivial getter functions: + + \snippet tools/customtype/message.h custom type definition + + The default constructor, copy constructor and destructor are + all required, and must be public, if the type is to be integrated into the + meta-object system. Other than this, we are free to implement whatever we + need to make the type do what we want, so we also include a constructor + that lets us set the type's data members. + + To enable the type to be used with QVariant, we declare it using the + Q_DECLARE_METATYPE() macro: + + \snippet tools/customtype/message.h custom type meta-type declaration + + We do not need to write any additional code to accompany this macro. + + To allow us to see a readable description of each \c Message object when it + is sent to the debug output stream, we define a streaming operator: + + \snippet tools/customtype/message.h custom type streaming operator + + This facility is useful if you need to insert tracing statements in your + code for debugging purposes. + + \section1 The Message Class Implementation + + The implementation of the default constructor, copy constructor and destructor + are straightforward for the \c Message class: + + \snippet tools/customtype/message.cpp Message class implementation + + The streaming operator is implemented in the following way: + + \snippet tools/customtype/message.cpp custom type streaming operator + + Here, we want to represent each value depending on how many lines are stored + in the message body. We stream text to the QDebug object passed to the + operator and return the QDebug object obtained from its maybeSpace() member + function; this is described in more detail in the + \l{Creating Custom Qt Types#Making the Type Printable}{Creating Custom Qt Types} + document. + + We include the code for the getter functions for completeness: + + \snippet tools/customtype/message.cpp getter functions + + With the type fully defined, implemented, and integrated with the + meta-object system, we can now use it. + + \section1 Using the Message + + In the example's \c{main()} function, we show how a \c Message object can + be printed to the console by sending it to the debug stream: + + \snippet tools/customtype/main.cpp printing a custom type + + You can use the type with QVariant in exactly the same way as you would + use standard Qt value types. Here's how to store a value using the + QVariant::setValue() function: + + \snippet tools/customtype/main.cpp storing a custom value + + Alternatively, the QVariant::fromValue() and qVariantSetValue() functions + can be used if you are using a compiler without support for member template + functions. + + The value can be retrieved using the QVariant::value() member template + function: + + \snippet tools/customtype/main.cpp retrieving a custom value + + Alternatively, the qVariantValue() template function can be used if + you are using a compiler without support for member template functions. + + \section1 Further Reading + + The custom \c Message type can also be used with direct signal-slot + connections. + + To register a custom type for use with queued signals and slots, such as + those used in cross-thread communication, see the + \l{Queued Custom Type Example}. + + More information on using custom types with Qt can be found in the + \l{Creating Custom Qt Types} document. +*/ |