gtk2/docs/reference/gtk/tree_widget.sgml

<refentry id="TreeWidget" revision="20 Mar 2002">
  <refmeta>
    <refentrytitle>Tree and List Widget Overview</refentrytitle>
    <manvolnum>3</manvolnum>
    <refmiscinfo>GTK Library</refmiscinfo>
  </refmeta>

  <refnamediv>
    <refname>Tree and List Widget Overview</refname>
    <refpurpose>Overview of <link
    linkend="GtkTreeModel">GtkTreeModel</link>, <link
    linkend="GtkTreeView">GtkTreeView</link>, and other associated widgets</refpurpose>
  </refnamediv>

  <refsect1>
    <title>Overview</title>
    <para>
      To create a tree or list in GTK+, you need to use the <link
      linkend="GtkTreeModel">GtkTreeModel</link> interface, in
      conjunction with the <link
      linkend="GtkTreeView">GtkTreeView</link> widget.
    </para>
    <para>
      This widget is designed around a
      <firstterm>Model/View/Controller</firstterm> design and consists
      of four major parts:
      <simplelist>
	<member>the tree view widget (<structname>GtkTreeView</structname>)</member>
	<member>the view column (<structname>GtkTreeViewColumn</structname>)</member>
	<member>the cell renderers (<structname>GtkCellRenderer</structname> etc.)</member>
	<member>and the model interface (<structname>GtkTreeModel</structname>)</member>
      </simplelist>
      The <emphasis>View</emphasis> is composed of the first three,
	while the last is the <emphasis>Model</emphasis>.  One of the
	prime benefits of the MVC design is that multiple views can be
	created of a single model.  For example, a model mapping the file
	system could be created for a file manager.  Many views could be
	created to display various parts of the file system, but only one
	copy need be kept in memory.
    </para>
    <para>
        The purpose of the cell renderers is to provide extensibility to the
        widget and to allow multiple ways of rendering the same type of data.
        For example, consider how to render a boolean variable.  Should you
        render it as a string of "True" or "False", "On" or "Off", or should
        you render it as a checkbox?
    </para>
  </refsect1>
  <refsect1>
    <title>Creating a model</title>
    <para>
      GTK+ 2.0 provides two types of models that can be used:
      <link linkend="GtkListStore">GtkListStore</link> and
      <link linkend="GtkTreeStore">GtkTreeStore</link>.  GtkListStore is
      used to model columned list widgets, while GtkTreeStore models
      columned tree widgets.  It is possible to develop a new type of model,
      but the existing models should be satisfactory for all but the most
      specialized of situations.  Creating the model is quite simple:
    </para>
      <informalexample><programlisting><![CDATA[
GtkListStore *store = gtk_list_store_new (2, G_TYPE_STRING, G_TYPE_BOOLEAN);
]]></programlisting></informalexample>
    <para>
      This creates a list store with two columns: a string column and a boolean
      column.  Typically the 2 is never passed directly like that; usually an
      enum is created wherein the different columns are enumerated, followed by
      a token that represents the total number of columns.  The next example will
      illustrate this, only using a tree store instead of a list store. Creating
      a tree store operates almost exactly the same.
    </para>
    <informalexample><programlisting><![CDATA[
enum
{
   TITLE_COLUMN,
   AUTHOR_COLUMN,
   CHECKED_COLUMN,
   N_COLUMNS
};

GtkTreeStore *store = gtk_tree_store_new (N_COLUMNS,       /* Total number of columns */
                                          G_TYPE_STRING,   /* Book title              */
                                          G_TYPE_STRING,   /* Author                  */
                                          G_TYPE_BOOLEAN); /* Is checked out?         */
]]></programlisting></informalexample>
    <para>
      Adding data to the model is done using <link linkend="gtk_tree_store_set">
      gtk_tree_store_set()</link> or <link linkend="gtk_list_store_set">
      gtk_list_store_set()</link>, depending upon which sort of model was
      created.  To do this, a <link linkend="GtkTreeIter">GtkTreeIter</link> must
      be acquired.  The iterator points to the location where data will be added.
    </para>
    <para>
      Once an iterator has been acquired, <link linkend="gtk_tree_store_set">
      gtk_tree_store_set()</link> is used to apply data to the part of the model
      that the iterator points to.  Consider the following example:
    </para>
    <informalexample><programlisting><![CDATA[
GtkTreeIter   iter;

gtk_tree_store_append (store, &iter, NULL);  /* Acquire an iterator */

gtk_tree_store_set (store, &iter,
                    TITLE_COLUMN, "The Principle of Reason",
                    AUTHOR_COLUMN, "Martin Heidegger",
                    CHECKED_COLUMN, FALSE
                    -1);
]]></programlisting></informalexample>

  <para>
    Notice that the last argument is -1.  This is always done because
    this is a variable-argument function and it needs to know when to stop
    processing arguments.  It can be used to set the data in any or all
    columns in a given row.
  </para>
  <para>
    The third argument to gtk_tree_store_append() is the parent iterator.  It
    is used to add a row to a GtkTreeStore as a child of an existing row.  This
    means that the new row will only be visible when its parent is visible and
    in its expanded state.  Consider the following example:
  </para>
  <informalexample><programlisting><![CDATA[
GtkTreeIter iter1;  /* Parent iter */
GtkTreeIter iter2;  /* Child iter  */

gtk_tree_store_append (store, &iter1, NULL);  /* Acquire a top-level iterator */
gtk_tree_store_set (store, &iter1,
                    TITLE_COLUMN, "The Art of Computer Programming",
                    AUTHOR_COLUMN, "Donald E. Knuth",
                    CHECKED_COLUMN, FALSE,
                    -1);

gtk_tree_store_append (store, &iter2, &iter1);  /* Acquire a child iterator */
gtk_tree_store_set (store, &iter2,
                    TITLE_COLUMN, "Volume 1: Fundamental Algorithms",
                    -1);

gtk_tree_store_append (store, &iter2, &iter1);
gtk_tree_store_set (store, &iter2,
                    TITLE_COLUMN, "Volume 2: Seminumerical Algorithms",
                    -1);

gtk_tree_store_append (store, &iter2, &iter1);
gtk_tree_store_set (store, &iter2,
                    TITLE_COLUMN, "Volume 3: Sorting and Searching",
                    -1);
]]></programlisting></informalexample>
  </refsect1>

  <refsect1>
    <title>Creating the view component</title>
    <para>
      While there are several different models to choose from, there is
      only one view widget to deal with.  It works with either the list
      or the tree store.  Setting up a <link
      linkend="GtkTreeView">GtkTreeView</link> is not a difficult
      matter.  It needs a <link
      linkend="GtkTreeModel">GtkTreeModel</link> to know where to
      retrieve its data from.
    </para>
    <informalexample><programlisting><![CDATA[
GtkWidget *tree;

tree = gtk_tree_view_new_with_model (GTK_TREE_MODEL (store));
]]></programlisting></informalexample>

    <refsect2>
      <title>Columns and cell renderers</title>
      <para>
	Once the <link linkend="GtkTreeView">GtkTreeView</link> widget
	has a model, it will need to know how to display the model.  It
	does this with columns and cell renderers.
      </para>
      <para>
        Cell renderers are used to draw the data in the tree model in a
        way.  There are three cell renderers that come with GTK+ 2.0.
        They are the <link
        linkend="GtkCellRendererText">GtkCellRendererText</link>, <link
        linkend="GtkCellRendererPixbuf">GtkCellRendererPixbuf</link> and
        the <link
        linkend="GtkCellRendererToggle">GtkCellRendererToggle</link>.
        It is relatively easy to write a custom renderer.
      </para>
      <para>
        A <link linkend="GtkTreeViewColumn">GtkTreeViewColumn</link> is the
        object that GtkTreeView uses to organize the vertical columns in
        the tree view.  It needs to know the name of the column to label
        for the user, what type of cell renderer to use, and which piece of
        data to retrieve from the model for a given row.
      </para>
      <informalexample><programlisting><![CDATA[
GtkCellRenderer *renderer;
GtkTreeViewColumn *column;

renderer = gtk_cell_renderer_text_new ();
column = gtk_tree_view_column_new_with_attributes ("Author",
                                                   renderer,
                                                   "text", AUTHOR_COLUMN,
                                                   NULL);
gtk_tree_view_append_column (GTK_TREE_VIEW (tree), column);
]]></programlisting></informalexample>
      <para>
       At this point, all the steps in creating a displayable tree have been
       covered.  The model is created, data is stored in it, a tree view is
       created and columns are added to it.
      </para>
    </refsect2>

    <refsect2>
      <title>Selection handling</title>
      <para>
        Most applications will need to not only deal with displaying data, but also
        receiving input events from users.  To do this, simply get a reference to
        a selection object and connect to the "changed" signal.
      </para>
      <informalexample><programlisting><![CDATA[
/* Prototype for selection handler callback */
static void tree_selection_changed_cb (GtkTreeSelection *selection, gpointer data);

/* Setup the selection handler */
GtkTreeSelection *select;

select = gtk_tree_view_get_selection (GTK_TREE_VIEW (tree));
gtk_tree_selection_set_mode (select, GTK_SELECT_SINGLE);
g_signal_connect (G_OBJECT (select), "changed",
                  G_CALLBACK (tree_selection_changed_cb),
                  NULL);
]]></programlisting></informalexample>
        <para>
          Then to retrieve data for the row selected:
        </para>
        <informalexample><programlisting><![CDATA[
static void
tree_selection_changed_cb (GtkTreeSelection *selection, gpointer data)
{
        GtkTreeIter iter;
        GtkTreeModel *model;
        gchar *author;

        if (gtk_tree_selection_get_selected (selection, &model, &iter))
        {
                gtk_tree_model_get (model, &iter, AUTHOR_COLUMN, &author, -1);

                g_print ("You selected a book by %s\n", author);

                g_free (author);
        }
}
]]></programlisting></informalexample>
    </refsect2>
  </refsect1>

  <refsect1>
    <title>Simple Example</title>
    <para>
      Here is a simple example of using a <link
      linkend="GtkTreeView">GtkTreeView</link> widget in context of the
      other widgets.  It simply creates a simple model and view, and
      puts them together.  Note that the model is never populated with
      data &mdash; that is left as an exercise for the reader.  More
      information can be found on this in the <link
      linkend="GtkTreeStore">GtkTreeModel</link> section.
      <informalexample><programlisting><![CDATA[
enum
{
   TITLE_COLUMN,
   AUTHOR_COLUMN,
   CHECKED_COLUMN,
   N_COLUMNS
};

void
setup_tree (void)
{
   GtkTreeStore *store;
   GtkWidget *tree;
   GtkTreeViewColumn *column;
   GtkCellRenderer *renderer;

   /* Create a model.  We are using the store model for now, though we
    * could use any other GtkTreeModel */
   store = gtk_tree_store_new (N_COLUMNS,
                               G_TYPE_STRING,
                               G_TYPE_STRING,
                               G_TYPE_BOOLEAN);

   /* custom function to fill the model with data */
   populate_tree_model (store);

   /* Create a view */
   tree = gtk_tree_view_new_with_model (GTK_TREE_MODEL (store));

   /* The view now holds a reference.  We can get rid of our own
    * reference */
   g_object_unref (G_OBJECT (store));

   /* Create a cell render and arbitrarily make it red for demonstration
    * purposes */
   renderer = gtk_cell_renderer_text_new ();
   g_object_set (G_OBJECT (renderer),
                 "foreground", "red",
                 NULL);

   /* Create a column, associating the "text" attribute of the
    * cell_renderer to the first column of the model */
   column = gtk_tree_view_column_new_with_attributes ("Author", renderer,
                                                      "text", AUTHOR_COLUMN,
                                                      NULL);

   /* Add the column to the view. */
   gtk_tree_view_append_column (GTK_TREE_VIEW (tree), column);

   /* Second column.. title of the book. */
   renderer = gtk_cell_renderer_text_new ();
   column = gtk_tree_view_column_new_with_attributes ("Title",
                                                      renderer,
                                                      "text", TITLE_COLUMN,
                                                      NULL);
   gtk_tree_view_append_column (GTK_TREE_VIEW (tree), column);

   /* Last column.. whether a book is checked out. */
   renderer = gtk_cell_renderer_toggle_new ();
   column = gtk_tree_view_column_new_with_attributes ("Checked out",
                                                      renderer,
                                                      "active", CHECKED_COLUMN,
                                                      NULL);
   gtk_tree_view_append_column (GTK_TREE_VIEW (tree), column);

   /* Now we can manipulate the view just like any other GTK widget */
   ...
}
]]>
      </programlisting></informalexample>
    </para>
  </refsect1>
</refentry>