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<h1 align="center">Using Models and Views<br /><small></small></h1>
<ul><li><a href="#introduction">Introduction</a></li>
<li><a href="#using-views-with-an-existing-model">Using Views with an Existing Model</a></li>
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<a name="introduction"></a>
<h2>Introduction</h2>
<p>Two of the standard models provided by Qt are <a href="gui/QStandardItemModel.html"><tt>QStandardItemModel</tt></a> and <a href="gui/QDirModel.html"><tt>QDirModel</tt></a>. <a href="gui/QStandardItemModel.html"><tt>QStandardItemModel</tt></a> is a multi-purpose model that can be used to represent various different data structures needed by list, table, and tree views. This model also holds the items of data. <a href="gui/QDirModel.html"><tt>QDirModel</tt></a> is a model that maintains information about the contents of a directory. As a result, it does not hold any items of data itself, but simply represents files and directories on the local filing system.</p>
<p><a href="gui/QDirModel.html"><tt>QDirModel</tt></a> provides a ready-to-use model to experiment with, and can be easily configured to use existing data. Using this model, we can show how to set up a model for use with ready-made views, and explore how to manipulate data using model indexes.</p>
<a name="using-views-with-an-existing-model"></a>
<h2>Using Views with an Existing Model</h2>
<p>The <a href="gui/QListView.html"><tt>QListView</tt></a> and <a href="gui/QTreeView.html"><tt>QTreeView</tt></a> classes are the most suitable views to use with <a href="gui/QDirModel.html"><tt>QDirModel</tt></a>. The example presented below displays the contents of a directory in a tree view next to the same information in a list view. The views share the user's selection so that the selected items are highlighted in both views.</p>
<p align="center"><img src="images/shareddirmodel.png" /></p><p>We set up a <a href="gui/QDirModel.html"><tt>QDirModel</tt></a> so that it is ready for use, and create some views to display the contents of a directory. This shows the simplest way to use a model. The construction and use of the model is performed from within a single <tt>main()</tt> function:</p>
<pre> int main(int argc, char *argv[])
{
QApplication app(argc, argv);
QSplitter *splitter = new QSplitter;
QDirModel *model = new QDirModel;</pre>
<p>The model is set up to use data from a default directory. We create two views so that we can examine the items held in the model in two different ways:</p>
<pre> QTreeView *tree = new QTreeView(splitter);
tree->setModel(model);
tree->setRootIndex(model->index(QDir::currentPath()));
QListView *list = new QListView(splitter);
list->setModel(model);
list->setRootIndex(model->index(QDir::currentPath()));</pre>
<p>The views are constructed in the same way as other widgets. Setting up a view to display the items in the model is simply a matter of calling its setModel() function with the directory model as the argument. The calls to setRootIndex() tell the views which directory to display by supplying a <i>model index</i> that we obtain from the directory model.</p>
<p>The <tt>index()</tt> function used in this case is unique to <a href="gui/QDirModel.html"><tt>QDirModel</tt></a>; we supply it with a directory and it returns a model index. Model indexes are discussed in the <a href="model-view-model.html">Model Classes</tt></a> chapter.</p>
<p>The rest of the function just displays the views within a splitter widget, and runs the application's event loop:</p>
<pre> splitter->setWindowTitle("Two views onto the same directory model");
splitter->show();
return app.exec();
}</pre>
<p>In the above example, we neglected to mention how to handle selections of items. This subject is covered in more detail in the chapter on <a href="model-view-selection.html">Handling Selections in Item Views</tt></a>. Before examining how selections are handled, you may find it useful to read the <a href="model-view-model.html">Model Classes</tt></a> chapter which describes the concepts used in the model/view framework.</p>
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