<?xml version="1.0" encoding="iso-8859-1"?>
<!DOCTYPE html
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<!-- addressbook.qdoc -->
<head>
<title>Qt 4.6: Address Book 3 - Navigating between Entries</title>
<link rel="prev" href="tutorials-addressbook-part2.html" />
<link rel="contents" href="tutorials-addressbook.html" />
<link rel="next" href="tutorials-addressbook-part4.html" />
<link href="classic.css" rel="stylesheet" type="text/css" />
</head>
<body>
<table border="0" cellpadding="0" cellspacing="0" width="100%">
<tr>
<td align="left" valign="top" width="32"><a href="http://qt.nokia.com/"><img src="images/qt-logo.png" align="left" border="0" /></a></td>
<td width="1"> </td><td class="postheader" valign="center"><a href="index.html"><font color="#004faf">Home</font></a> · <a href="classes.html"><font color="#004faf">All Classes</font></a> · <a href="functions.html"><font color="#004faf">All Functions</font></a> · <a href="overviews.html"><font color="#004faf">Overviews</font></a></td></tr></table><p>
[Previous: <a href="tutorials-addressbook-part2.html">Address Book 2 - Adding Addresses</a>]
[<a href="tutorials-addressbook.html">Contents</a>]
[Next: <a href="tutorials-addressbook-part4.html">Chapter 4</a>]
</p>
<h1 class="title">Address Book 3 - Navigating between Entries<br /><span class="subtitle"></span>
</h1>
<p>Files:</p>
<ul>
<li><a href="tutorials-addressbook-part3-addressbook-cpp.html">tutorials/addressbook/part3/addressbook.cpp</a></li>
<li><a href="tutorials-addressbook-part3-addressbook-h.html">tutorials/addressbook/part3/addressbook.h</a></li>
<li><a href="tutorials-addressbook-part3-main-cpp.html">tutorials/addressbook/part3/main.cpp</a></li>
<li><a href="tutorials-addressbook-part3-part3-pro.html">tutorials/addressbook/part3/part3.pro</a></li>
</ul>
<p>The address book application is now half complete. We need to add some functions to navigate between contacts. But first, we have to decide what sort of a data structure we would like to use to hold these contacts.</p>
<p>In Chapter 2, we used a <a href="qmap.html">QMap</a> of key-value pairs with the contact's name as the <i>key</i>, and the contact's address as the <i>value</i>. This works well for our case. However, in order to navigate and display each entry, a little bit of enhancement is needed.</p>
<p>We enhance the <a href="qmap.html">QMap</a> by making it replicate a data structure similar to a circularly-linked list, where all elements are connected, including the first element and the last element. The figure below illustrates this data structure.</p>
<p align="center"><img src="images/addressbook-tutorial-part3-linkedlist.png" /></p><a name="defining-the-addressbook-class"></a>
<h2>Defining the AddressBook Class</h2>
<p>In order to add navigation functions to the address book application, we need to add two more slots to our <tt>AddressBook</tt> class: <tt>next()</tt> and <tt>previous()</tt>. These are added to our <tt>addressbook.h</tt> file:</p>
<pre> void next();
void previous();</pre>
<p>We also require another two <a href="qpushbutton.html">QPushButton</a> objects, so we declare <tt>nextButton</tt> and <tt>previousButton</tt> as private variables:</p>
<pre> QPushButton *nextButton;
QPushButton *previousButton;</pre>
<a name="implementing-the-addressbook-class"></a>
<h2>Implementing the AddressBook Class</h2>
<p>In the <tt>AddressBook</tt> constructor in <tt>addressbook.cpp</tt>, we instantiate <tt>nextButton</tt> and <tt>previousButton</tt> and disable them by default. This is because navigation is only enabled when there is more than one contact in the address book.</p>
<pre> nextButton = new QPushButton(tr("&Next"));
nextButton->setEnabled(false);
previousButton = new QPushButton(tr("&Previous"));
previousButton->setEnabled(false);</pre>
<p>We then connect these push buttons to their respective slots:</p>
<pre> connect(nextButton, SIGNAL(clicked()), this, SLOT(next()));
connect(previousButton, SIGNAL(clicked()), this, SLOT(previous()));</pre>
<p>The image below is our expected graphical user interface. Notice that it is getting closer to our final application.</p>
<p align="center"><img src="images/addressbook-tutorial-part3-screenshot.png" /></p><p>We follow basic conventions for <tt>next()</tt> and <tt>previous()</tt> functions by placing the <tt>nextButton</tt> on the right and the <tt>previousButton</tt> on the left. In order to achieve this intuitive layout, we use <a href="qhboxlayout.html">QHBoxLayout</a> to place the widgets side-by-side:</p>
<pre> QHBoxLayout *buttonLayout2 = new QHBoxLayout;
buttonLayout2->addWidget(previousButton);
buttonLayout2->addWidget(nextButton);</pre>
<p>The <a href="qhboxlayout.html">QHBoxLayout</a> object, <tt>buttonLayout2</tt>, is then added to <tt>mainLayout</tt>.</p>
<pre> mainLayout->addLayout(buttonLayout2, 3, 1);</pre>
<p>The figure below shows the coordinates of the widgets in <tt>mainLayout</tt>.</p>
<p align="center"><img src="images/addressbook-tutorial-part3-labeled-layout.png" /></p><p>Within our <tt>addContact()</tt> function, we have to disable these buttons so that the user does not attempt to navigate while adding a contact.</p>
<pre> nextButton->setEnabled(false);
previousButton->setEnabled(false);</pre>
<p>Also, in our <tt>submitContact()</tt> function, we enable the navigation buttons, <tt>nextButton</tt> and <tt>previousButton</tt>, depending on the size of <tt>contacts</tt>. As mentioned earlier, navigation is only enabled when there is more than one contact in the address book. The following lines of code demonstrates how to do this:</p>
<pre> int number = contacts.size();
nextButton->setEnabled(number > 1);
previousButton->setEnabled(number > 1);</pre>
<p>We also include these lines of code in the <tt>cancel()</tt> function.</p>
<p>Recall that we intend to emulate a circularly-linked list with our <a href="qmap.html">QMap</a> object, <tt>contacts</tt>. So, in the <tt>next()</tt> function, we obtain an iterator for <tt>contacts</tt> and then:</p>
<ul>
<li>If the iterator is not at the end of <tt>contacts</tt>, we increment it by one.</li>
<li>If the iterator is at the end of <tt>contacts</tt>, we move it to the beginning of <tt>contacts</tt>. This gives us the illusion that our <a href="qmap.html">QMap</a> is working like a circularly-linked list.</li>
</ul>
<pre> void AddressBook::next()
{
QString name = nameLine->text();
QMap<QString, QString>::iterator i = contacts.find(name);
if (i != contacts.end())
i++;
if (i == contacts.end())
i = contacts.begin();
nameLine->setText(i.key());
addressText->setText(i.value());
}</pre>
<p>Once we have iterated to the correct object in <tt>contacts</tt>, we display its contents on <tt>nameLine</tt> and <tt>addressText</tt>.</p>
<p>Similarly, for the <tt>previous()</tt> function, we obtain an iterator for <tt>contacts</tt> and then:</p>
<ul>
<li>If the iterator is at the end of <tt>contacts</tt>, we clear the display and return.</li>
<li>If the iterator is at the beginning of <tt>contacts</tt>, we move it to the end.</li>
<li>We then decrement the iterator by one.</li>
</ul>
<pre> void AddressBook::previous()
{
QString name = nameLine->text();
QMap<QString, QString>::iterator i = contacts.find(name);
if (i == contacts.end()){
nameLine->clear();
addressText->clear();
return;
}
if (i == contacts.begin())
i = contacts.end();
i--;
nameLine->setText(i.key());
addressText->setText(i.value());
}</pre>
<p>Again, we display the contents of the current object in <tt>contacts</tt>.</p>
<p>
[Previous: <a href="tutorials-addressbook-part2.html">Address Book 2 - Adding Addresses</a>]
[<a href="tutorials-addressbook.html">Contents</a>]
[Next: <a href="tutorials-addressbook-part4.html">Chapter 4</a>]
</p>
<p /><address><hr /><div align="center">
<table width="100%" cellspacing="0" border="0"><tr class="address">
<td width="40%" align="left">Copyright © 2010 Nokia Corporation and/or its subsidiary(-ies)</td>
<td width="20%" align="center"><a href="trademarks.html">Trademarks</a></td>
<td width="40%" align="right"><div align="right">Qt 4.6.3</div></td>
</tr></table></div></address></body>
</html>
distrib
>
Mandriva
>
current
>
i586
>
media
>
main-updates
>
by-pkgid
>
8e6051afcdb111a0317a58fb64c2abf5
>
files
>
6120
