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<h3><a name="toc">Contents</a></h3>
<ul>
<li class="level1"><a href="#defining-the-addressbook-class">Defining the AddressBook Class</a></li>
<li class="level1"><a href="#implementing-the-addressbook-class">Implementing the AddressBook Class</a></li>
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<h1 class="title">Part 3 - Navigating between Entries</h1>
<span class="subtitle"></span>
<!-- $$$tutorials/addressbook/part3-description -->
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<p>Files:</p>
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<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>
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<p>The address book is now about half complete. We should add the capability to navigate among the contacts, but first we must decide what sort of a data structure we need for containing these contacts.</p>
<p>In the previous section, 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 class="centerAlign"><img src="images/addressbook-tutorial-part3-linkedlist.png" alt="" /></p><a name="defining-the-addressbook-class"></a>
<h2>Defining the AddressBook Class</h2>
<p>To add navigation functions to the address book, we must add two more slots to the <tt>AddressBook</tt> class: <tt>next()</tt> and <tt>previous()</tt> to the <tt>addressbook.h</tt> file:</p>
<pre class="cpp"> <span class="type">void</span> next();
<span class="type">void</span> 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 class="cpp"> <span class="type"><a href="qpushbutton.html">QPushButton</a></span> <span class="operator">*</span>nextButton;
<span class="type"><a href="qpushbutton.html">QPushButton</a></span> <span class="operator">*</span>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 class="cpp"> nextButton <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qpushbutton.html">QPushButton</a></span>(tr(<span class="string">"&Next"</span>));
nextButton<span class="operator">-</span><span class="operator">></span>setEnabled(<span class="keyword">false</span>);
previousButton <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qpushbutton.html">QPushButton</a></span>(tr(<span class="string">"&Previous"</span>));
previousButton<span class="operator">-</span><span class="operator">></span>setEnabled(<span class="keyword">false</span>);</pre>
<p>We then connect these push buttons to their respective slots:</p>
<pre class="cpp"> connect(nextButton<span class="operator">,</span> SIGNAL(clicked())<span class="operator">,</span> <span class="keyword">this</span><span class="operator">,</span> SLOT(next()));
connect(previousButton<span class="operator">,</span> SIGNAL(clicked())<span class="operator">,</span> <span class="keyword">this</span><span class="operator">,</span> SLOT(previous()));</pre>
<p>The image below is the expected graphical user interface.</p>
<p class="centerAlign"><img src="images/addressbook-tutorial-part3-screenshot.png" alt="" /></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 class="cpp"> <span class="type"><a href="qhboxlayout.html">QHBoxLayout</a></span> <span class="operator">*</span>buttonLayout2 <span class="operator">=</span> <span class="keyword">new</span> <span class="type"><a href="qhboxlayout.html">QHBoxLayout</a></span>;
buttonLayout2<span class="operator">-</span><span class="operator">></span>addWidget(previousButton);
buttonLayout2<span class="operator">-</span><span class="operator">></span>addWidget(nextButton);</pre>
<p>The <a href="qhboxlayout.html">QHBoxLayout</a> object, <tt>buttonLayout2</tt>, is then added to <tt>mainLayout</tt>.</p>
<pre class="cpp"> mainLayout<span class="operator">-</span><span class="operator">></span>addLayout(buttonLayout2<span class="operator">,</span> <span class="number">2</span><span class="operator">,</span> <span class="number">1</span>);</pre>
<p>The figure below shows the coordinates of the widgets in <tt>mainLayout</tt>.</p>
<p class="centerAlign"><img src="images/addressbook-tutorial-part3-labeled-layout.png" alt="" /></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 class="cpp"> nextButton<span class="operator">-</span><span class="operator">></span>setEnabled(<span class="keyword">false</span>);
previousButton<span class="operator">-</span><span class="operator">></span>setEnabled(<span class="keyword">false</span>);</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 class="cpp"> <span class="type">int</span> number <span class="operator">=</span> contacts<span class="operator">.</span>size();
nextButton<span class="operator">-</span><span class="operator">></span>setEnabled(number <span class="operator">></span> <span class="number">1</span>);
previousButton<span class="operator">-</span><span class="operator">></span>setEnabled(number <span class="operator">></span> <span class="number">1</span>);</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 class="cpp"> <span class="type">void</span> AddressBook<span class="operator">::</span>next()
{
<span class="type"><a href="qstring.html">QString</a></span> name <span class="operator">=</span> nameLine<span class="operator">-</span><span class="operator">></span>text();
<span class="type"><a href="qmap.html">QMap</a></span><span class="operator"><</span><span class="type"><a href="qstring.html">QString</a></span><span class="operator">,</span> <span class="type"><a href="qstring.html">QString</a></span><span class="operator">></span><span class="operator">::</span>iterator i <span class="operator">=</span> contacts<span class="operator">.</span>find(name);
<span class="keyword">if</span> (i <span class="operator">!</span><span class="operator">=</span> contacts<span class="operator">.</span>end())
i<span class="operator">+</span><span class="operator">+</span>;
<span class="keyword">if</span> (i <span class="operator">=</span><span class="operator">=</span> contacts<span class="operator">.</span>end())
i <span class="operator">=</span> contacts<span class="operator">.</span>begin();
nameLine<span class="operator">-</span><span class="operator">></span>setText(i<span class="operator">.</span>key());
addressText<span class="operator">-</span><span class="operator">></span>setText(i<span class="operator">.</span>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 class="cpp"> <span class="type">void</span> AddressBook<span class="operator">::</span>previous()
{
<span class="type"><a href="qstring.html">QString</a></span> name <span class="operator">=</span> nameLine<span class="operator">-</span><span class="operator">></span>text();
<span class="type"><a href="qmap.html">QMap</a></span><span class="operator"><</span><span class="type"><a href="qstring.html">QString</a></span><span class="operator">,</span> <span class="type"><a href="qstring.html">QString</a></span><span class="operator">></span><span class="operator">::</span>iterator i <span class="operator">=</span> contacts<span class="operator">.</span>find(name);
<span class="keyword">if</span> (i <span class="operator">=</span><span class="operator">=</span> contacts<span class="operator">.</span>end()){
nameLine<span class="operator">-</span><span class="operator">></span>clear();
addressText<span class="operator">-</span><span class="operator">></span>clear();
<span class="keyword">return</span>;
}
<span class="keyword">if</span> (i <span class="operator">=</span><span class="operator">=</span> contacts<span class="operator">.</span>begin())
i <span class="operator">=</span> contacts<span class="operator">.</span>end();
i<span class="operator">-</span><span class="operator">-</span>;
nameLine<span class="operator">-</span><span class="operator">></span>setText(i<span class="operator">.</span>key());
addressText<span class="operator">-</span><span class="operator">></span>setText(i<span class="operator">.</span>value());
}</pre>
<p>Again, we display the contents of the current object in <tt>contacts</tt>.</p>
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