forked from AuroraMiddleware/gtk
284 lines
10 KiB
Markdown
284 lines
10 KiB
Markdown
Title: Tree and List Widget Overview
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Slug: gtk-treeview
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To create a tree or list in GTK, use the `GtkTreeModel` interface in
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conjunction with the `GtkTreeView` widget. This widget is designed around
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a _Model/View/Controller_ design and consists of four major parts:
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- The tree view widget (GtkTreeView)
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- The view column (GtkTreeViewColumn)
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- The cell renderers (GtkCellRenderer etc.)
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- The model interface (GtkTreeModel)
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The _View_ is composed of the first three objects, while the last is the
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_Model_. One of the prime benefits of the MVC design is that multiple views
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can be created of a single model. For example, a model mapping the file
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system could be created for a file manager. Many views could be created
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to display various parts of the file system, but only one copy need be
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kept in memory.
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The purpose of the cell renderers is to provide extensibility to the
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widget and to allow multiple ways of rendering the same type of data.
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For example, consider how to render a boolean variable. Should it
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render it as a string of "True" or "False", "On" or "Off", or should
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it be rendered as a checkbox?
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## Creating a model
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GTK provides two simple models that can be used: the `GtkListStore`
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and the `GtkTreeStore`. `GtkListStore` is used to model list widgets,
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while the `GtkTreeStore` models trees. It is possible to develop a new
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type of model, but the existing models should be satisfactory for all
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but the most specialized of situations. Creating the model is quite
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``` {.c}
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GtkListStore *store = gtk_list_store_new (2, G_TYPE_STRING, G_TYPE_BOOLEAN);
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```
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This creates a list store with two columns: a string column and a boolean
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column. Typically the 2 is never passed directly like that; usually an
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enum is created wherein the different columns are enumerated, followed by
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a token that represents the total number of columns. The next example will
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illustrate this, only using a tree store instead of a list store. Creating
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a tree store operates almost exactly the same.
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``` {.c}
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enum
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{
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TITLE_COLUMN,
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AUTHOR_COLUMN,
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CHECKED_COLUMN,
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N_COLUMNS
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};
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GtkTreeStore *store = gtk_tree_store_new (N_COLUMNS, /* Total number of columns */
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G_TYPE_STRING, /* Book title */
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G_TYPE_STRING, /* Author */
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G_TYPE_BOOLEAN); /* Is checked out? */
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```
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Adding data to the model is done using gtk_tree_store_set() or
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gtk_list_store_set(), depending upon which sort of model was
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created. To do this, a `GtkTreeIter` must be acquired. The iterator
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points to the location where data will be added.
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Once an iterator has been acquired, gtk_tree_store_set() is used to
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apply data to the part of the model that the iterator points to.
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Consider the following example:
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``` {.c}
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GtkTreeIter iter;
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gtk_tree_store_append (store, &iter, NULL); /* Acquire an iterator */
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gtk_tree_store_set (store, &iter,
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TITLE_COLUMN, "The Principle of Reason",
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AUTHOR_COLUMN, "Martin Heidegger",
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CHECKED_COLUMN, FALSE,
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-1);
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```
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Notice that the last argument is -1. This is always done because
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this is a variable-argument function and it needs to know when to stop
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processing arguments. It can be used to set the data in any or all
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columns in a given row.
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The third argument to gtk_tree_store_append() is the parent iterator.
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It is used to add a row to a GtkTreeStore as a child of an existing row.
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This means that the new row will only be visible when its parent is visible
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and in its expanded state. Consider the following example:
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``` {.c}
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GtkTreeIter iter1; /* Parent iter */
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GtkTreeIter iter2; /* Child iter */
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gtk_tree_store_append (store, &iter1, NULL); /* Acquire a top-level iterator */
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gtk_tree_store_set (store, &iter1,
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TITLE_COLUMN, "The Art of Computer Programming",
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AUTHOR_COLUMN, "Donald E. Knuth",
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CHECKED_COLUMN, FALSE,
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-1);
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gtk_tree_store_append (store, &iter2, &iter1); /* Acquire a child iterator */
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gtk_tree_store_set (store, &iter2,
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TITLE_COLUMN, "Volume 1: Fundamental Algorithms",
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-1);
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gtk_tree_store_append (store, &iter2, &iter1);
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gtk_tree_store_set (store, &iter2,
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TITLE_COLUMN, "Volume 2: Seminumerical Algorithms",
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-1);
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gtk_tree_store_append (store, &iter2, &iter1);
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gtk_tree_store_set (store, &iter2,
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TITLE_COLUMN, "Volume 3: Sorting and Searching",
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-1);
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```
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## Creating the view component
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While there are several different models to choose from, there is
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only one view widget to deal with. It works with either the list
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or the tree store. Setting up a `GtkTreeView` is not a difficult
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matter. It needs a `GtkTreeModel` to know where to retrieve its data
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from.
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``` {.c}
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GtkWidget *tree;
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tree = gtk_tree_view_new_with_model (GTK_TREE_MODEL (store));
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```
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## Columns and cell renderers
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Once the `GtkTreeView` widget has a model, it will need to know how
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to display the model. It does this with columns and cell renderers.
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Cell renderers are used to draw the data in the tree model in a
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way. There are a number of cell renderers that come with GTK,
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including the `GtkCellRendererText`, `GtkCellRendererPixbuf` and
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the `GtkCellRendererToggle`. It is relatively easy to write a
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custom renderer.
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A `GtkTreeViewColumn` is the object that `GtkTreeView` uses to organize
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the vertical columns in the tree view. It needs to know the name of
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the column to label for the user, what type of cell renderer to use,
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and which piece of data to retrieve from the model for a given row.
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``` {.c}
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GtkCellRenderer *renderer;
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GtkTreeViewColumn *column;
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renderer = gtk_cell_renderer_text_new (<!-- -->);
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column = gtk_tree_view_column_new_with_attributes ("Author",
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renderer,
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"text", AUTHOR_COLUMN,
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NULL);
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gtk_tree_view_append_column (GTK_TREE_VIEW (tree), column);
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```
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At this point, all the steps in creating a displayable tree have been
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covered. The model is created, data is stored in it, a tree view is
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created and columns are added to it.
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## Selection handling
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Most applications will need to not only deal with displaying data,
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but also receiving input events from users. To do this, simply get
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a reference to a selection object and connect to the
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`GtkTreeSelection::changed` signal.
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``` {.c}
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/* Prototype for selection handler callback */
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static void tree_selection_changed_cb (GtkTreeSelection *selection, gpointer data);
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/* Setup the selection handler */
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GtkTreeSelection *select;
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select = gtk_tree_view_get_selection (GTK_TREE_VIEW (tree));
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gtk_tree_selection_set_mode (select, GTK_SELECTION_SINGLE);
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g_signal_connect (G_OBJECT (select), "changed",
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G_CALLBACK (tree_selection_changed_cb),
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NULL);
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```
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Then to retrieve data for the row selected:
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``` {.c}
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static void
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tree_selection_changed_cb (GtkTreeSelection *selection, gpointer data)
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{
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GtkTreeIter iter;
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GtkTreeModel *model;
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char *author;
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if (gtk_tree_selection_get_selected (selection, &model, &iter))
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{
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gtk_tree_model_get (model, &iter, AUTHOR_COLUMN, &author, -1);
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g_print ("You selected a book by %s\n", author);
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g_free (author);
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}
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}
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```
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## Simple Example
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Here is a simple example of using a `GtkTreeView` widget in context
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of the other widgets. It simply creates a simple model and view,
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and puts them together. Note that the model is never populated
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with data — that is left as an exercise for the reader.
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More information can be found on this in the `GtkTreeModel` section.
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``` {.c}
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enum
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{
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TITLE_COLUMN,
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AUTHOR_COLUMN,
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CHECKED_COLUMN,
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N_COLUMNS
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};
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void
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setup_tree (void)
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{
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GtkTreeStore *store;
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GtkWidget *tree;
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GtkTreeViewColumn *column;
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GtkCellRenderer *renderer;
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/* Create a model. We are using the store model for now, though we
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* could use any other GtkTreeModel */
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store = gtk_tree_store_new (N_COLUMNS,
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G_TYPE_STRING,
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G_TYPE_STRING,
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G_TYPE_BOOLEAN);
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/* custom function to fill the model with data */
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populate_tree_model (store);
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/* Create a view */
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tree = gtk_tree_view_new_with_model (GTK_TREE_MODEL (store));
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/* The view now holds a reference. We can get rid of our own
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* reference */
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g_object_unref (G_OBJECT (store));
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/* Create a cell render and arbitrarily make it red for demonstration
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* purposes */
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renderer = gtk_cell_renderer_text_new (<!-- -->);
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g_object_set (G_OBJECT (renderer),
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"foreground", "red",
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NULL);
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/* Create a column, associating the "text" attribute of the
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* cell_renderer to the first column of the model */
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column = gtk_tree_view_column_new_with_attributes ("Author", renderer,
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"text", AUTHOR_COLUMN,
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NULL);
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/* Add the column to the view. */
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gtk_tree_view_append_column (GTK_TREE_VIEW (tree), column);
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/* Second column.. title of the book. */
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renderer = gtk_cell_renderer_text_new (<!-- -->);
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column = gtk_tree_view_column_new_with_attributes ("Title",
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renderer,
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"text", TITLE_COLUMN,
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NULL);
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gtk_tree_view_append_column (GTK_TREE_VIEW (tree), column);
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/* Last column.. whether a book is checked out. */
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renderer = gtk_cell_renderer_toggle_new (<!-- -->);
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column = gtk_tree_view_column_new_with_attributes ("Checked out",
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renderer,
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"active", CHECKED_COLUMN,
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NULL);
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gtk_tree_view_append_column (GTK_TREE_VIEW (tree), column);
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/* Now we can manipulate the view just like any other GTK widget */
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...
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}
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```
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