GTK+ 2.0 Tree View C接口教程详解

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Chapter 3. GtkTreeModels for Data Storage: GtkListStore and GtkTreeStore

model = gtk_tree_view_get_model(GTK_TREE_VIEW(view));

g_object_ref(model); /

Make sure the model stays with us after the tree view unrefs it

gtk_tree_view_set_model(GTK_TREE_VIEW(view), NULL); /

Detach model from view

... insert a couple of thousand rows ...

gtk_tree_view_set_model(GTK_TREE_VIEW(view), model); /

Re-attach model to view

g_object_unref(model);

...

Secondly, you should make sure that sorting is disabled while you are doing your mass insertions, otherwise your

store might be resorted after each and every single row insertion, which is going to be everything but fast.

Thirdly, you should not keep around a lot of tree row references if you have so many rows, because with each

insertion (or removal) every single tree row reference will check whether its path needs to be updated or not.

3.4. Manipulating Row Data

Adding empty rows to a data store is not terribly exciting, so let’s see how we can add or change data in the store.

gtk_list_store_set and gtk_tree_store_set are used to manipulate a given row’s data. There is also

gtk_list_store_set_value and gtk_tree_store_set_value, but those should only be used by people

familiar with GLib’s GValue system.

Both gtk_list_store_set and gtk_tree_store_set take a variable number of arguments, and must be termi-

nated with a -1 argument. The ﬁrst two arguments are a pointer to the model, and the iter pointing to the row

whose data we want to change. They are followed by a variable number of (column, data) argument pairs, termi-

nated by a -1. The column refers to the model column number and is usually an enum value (to make the code

more readable and to make changes easier). The data should be of the same data type as the model column.

Here is an example where we create a store that stores two strings and one integer for each row:

enum

{

COL_FIRST_NAME = 0,

COL_LAST_NAME,

COL_YEAR_BORN,

NUM_COLS

};

GtkListStore

liststore;

GtkTreeIter iter;

liststore = gtk_list_store_new(NUM_COLS, G_TYPE_STRING, G_TYPE_STRING, G_TYPE_UINT);

Append an empty row to the list store. Iter will point to the new row

gtk_list_store_append(liststore, &iter);

Fill fields with some data

gtk_list_store_set (liststore, &iter,

COL_FIRST_NAME, "Joe",

COL_LAST_NAME, "Average",

COL_YEAR_BORN, (guint) 1970,

-1);

You do not need to worry about allocating and freeing memory for the data to store. The model (or more precisely:

the GLib/GObject GType and GValue system) will take care of that for you. If you store a string, for example, the

model will make a copy of the string and store that. If you then set the ﬁeld to a new string later on, the model

will automatically free the old string and again make a copy of the new string and store the copy. This applies to

almost all types, be it G_TYPE_STRING or GDK_TYPE_PIXBUF.

The exception to note is G_TYPE_POINTER. If you allocate a chunk of data or a complex structure and store it

in a G_TYPE_POINTER ﬁeld, only the pointer value is stored. The model does not know anything about the size

or content of the data your pointer refers to, so it could not even make a copy if it wanted to, so you need to

Chapter 3. GtkTreeModels for Data Storage: GtkListStore and GtkTreeStore

allocate and free the memory yourself in this case. However, if you do not want to do that yourself and want the

model to take care of your custom data for you, then you need to register your own type and derive it from one

of the GLib fundamental types (usually G_TYPE_BOXED). See the GObject GType reference manual for details.

Making a copy of data involves memory allocation and other overhead of course, so one should consider the

performance implications of using a custom GLib type over a G_TYPE_POINTER carefully before taking that

approach. Again, a custom model might be the better alternative, depending on the overall amount of data to be

stored (and retrieved).

3.5. Retrieving Row Data

Storing data is not very useful if it cannot be retrieved again. This is done using gtk_tree_model_get, which

takes similar arguments as gtk_list_store_set or gtk_tree_store_set do, only that it takes (column, pointer)

arguments. The pointer must point to a variable that is of the same type as the data stored in that particular model

column.

Here is the previous example extended to traverse the list store and print out the data stored. As an extra, we use

gtk_tree_model_foreach to traverse the store and retrieve the row number from the GtkTreePath passed to us

in the foreach callback function:

#include <gtk/gtk.h>

enum

{

COL_FIRST_NAME = 0,

COL_LAST_NAME,

COL_YEAR_BORN,

NUM_COLS

};

gboolean

foreach_func (GtkTreeModel

model,

GtkTreePath

path,

GtkTreeIter

iter,

gpointer user_data)

{

gchar

first_name,

last_name,

tree_path_str;

guint year_of_birth;

Note: here we use ’iter’ and not ’&iter’, because we did not allocate

the iter on the stack and are already getting the pointer to a tree iter

gtk_tree_model_get (model, iter,

COL_FIRST_NAME, &first_name,

COL_LAST_NAME, &last_name,

COL_YEAR_BORN, &year_of_birth,

-1);

tree_path_str = gtk_tree_path_to_string(path);

g_print ("Row %s: %s %s, born %u\n", tree_path_str,

first_name, last_name, year_of_birth);

g_free(tree_path_str);

g_free(first_name); /

gtk_tree_model_get made copies of

g_free(last_name); /

the strings for us when retrieving them

return FALSE; /

do not stop walking the store, call us with next row

}

void

create_and_fill_and_dump_store (void)

{

GtkListStore

liststore;

GtkTreeIter iter;

liststore = gtk_list_store_new(NUM_COLS, G_TYPE_STRING, G_TYPE_STRING, G_TYPE_UINT);

Append an empty row to the list store. Iter will point to the new row

Chapter 3. GtkTreeModels for Data Storage: GtkListStore and GtkTreeStore

gtk_list_store_append(liststore, &iter);

Fill fields with some data

gtk_list_store_set (liststore, &iter,

COL_FIRST_NAME, "Joe",

COL_LAST_NAME, "Average",

COL_YEAR_BORN, (guint) 1970,

-1);

Append another row, and fill in some data

gtk_list_store_append(liststore, &iter);

gtk_list_store_set (liststore, &iter,

COL_FIRST_NAME, "Jane",

COL_LAST_NAME, "Common",

COL_YEAR_BORN, (guint) 1967,

-1);

Append yet another row, and fill it

gtk_list_store_append(liststore, &iter);

gtk_list_store_set (liststore, &iter,

COL_FIRST_NAME, "Yo",

COL_LAST_NAME, "Da",

COL_YEAR_BORN, (guint) 1873,

-1);

Now traverse the list

gtk_tree_model_foreach(GTK_TREE_MODEL(liststore), foreach_func, NULL);

}

int

main (int argc, char

argv)

{

gtk_init(&argc, &argv);

create_and_fill_and_dump_store();

return 0;

}

Note that when a new row is created, all ﬁelds of a row are set to a default NIL value appropriate for the data type

in question. A ﬁeld of type G_TYPE_INT will automatically contain the value 0 until it is set to a different value,

and strings and all kind of pointer types will be NULL until set to something else. Those are valid contents for the

model, and if you are not sure that row contents have been set to something, you need to be prepared to handle

NULL pointers and the like in your code.

Run the above program with an additional empty row and look at the output to see this in effect.

3.5.1. Freeing Retrieved Row Data

Unless you are dealing with a model column of type G_TYPE_POINTER, gtk_tree_model_get will always make

copies of the data retrieved.

In the case of strings, this means that you need to g_free the string returned when you don’t need it any longer,

as in the example above.

If you retrieve a GObject such as a GdkPixbuf from the store, gtk_tree_model_get will automatically add a

reference to it, so you need to call g_object_unref on the retrieved object once you are done with it:

...

GdkPixbuf

pixbuf;

gtk_tree_model_get (model, &iter,

COL_PICTURE, &pixbuf,

NULL);

Chapter 3. GtkTreeModels for Data Storage: GtkListStore and GtkTreeStore

if (pixbuf != NULL)

{

do_something_with_pixbuf (pixbuf);

g_object_unref (pixbuf);

}

...

Similarly, GBoxed-derived types retrieved from a model need to be freed with g_boxed_free when done with

them (don’t worry if you have never heard of GBoxed).

If the model column is of type G_TYPE_POINTER, gtk_tree_model_get will simply copy the pointer value, but not

the data (even if if it wanted to, it couldn’t copy the data, because it would not know how to copy it or what to

copy exactly). If you store pointers to objects or strings in a pointer column (which you should not do unless you

really know what you are doing and why you are doing it), you do not need to unref or free the returned values as

described above, because gtk_tree_model_get would not know what kind of data they are and therefore won’t

ref or copy them on retrieval.

3.6. Removing Rows

Rows can easily be removed with gtk_list_store_remove and gtk_tree_store_remove. The removed row

will automatically be removed from the tree view as well, and all data stored will automatically be freed, with the

exception of G_TYPE_POINTER columns (see above).

Removing a single row is fairly straight forward: you need to get the iter that identiﬁes the row you want to

remove, and then use one of the above functions. Here is a simple example that removes a row when you double-

click on it (bad from a user interface point of view, but then it is just an example):

static void

onRowActivated (GtkTreeView

view,

GtkTreePath

path,

GtkTreeViewColumn

col,

gpointer user_data)

{

GtkTreeModel

model;

GtkTreeIter iter;

g_print ("Row has been double-clicked. Removing row.\n");

model = gtk_tree_view_get_model(view);

if (!gtk_tree_model_get_iter(model, &iter, path))

return; /

path describes a non-existing row - should not happen

gtk_list_store_remove(GTK_LIST_STORE(model), &iter);

}

void

create_treeview (void)

{

...

g_signal_connect(treeview, "row-activated", G_CALLBACK(onRowActivated), NULL);

...

}

Note: gtk_list_store_remove and gtk_tree_store_remove both have slightly different semantics in Gtk+-

2.0 and Gtk+-2.2 and later. In Gtk+-2.0, both functions do not return a value, while in later Gtk+ versions those

functions return either TRUE or FALSE to indicate whether the iter given has been set to the next valid row (or

invalidated if there is no next row). This is important to keep in mind when writing code that is supposed to work

with all Gtk+-2.x versions. In that case you should just ignore the value returned (as in the call above) and check

the iter with gtk_list_store_iter_is_valid if you need it.

If you want to remove the n-th row from a list (or the n-th child of a tree node), you have two approaches: either

you ﬁrst create a GtkTreePath that describes that row and then turn it into an iter and remove it; or you take the

Chapter 3. GtkTreeModels for Data Storage: GtkListStore and GtkTreeStore

iter of the parent node and use gtk_tree_model_iter_nth_child (which will also work for list stores if you use

NULL as the parent iter. Of course you could also start with the iter of the ﬁrst top-level row, and then step-by-step

move it to the row you want, although that seems a rather awkward way of doing it.

The following code snippet will remove the n-th row of a list if it exists:

******************************************************************

list_store_remove_nth_row

Removes the nth row of a list store if it exists.

Returns TRUE on success or FALSE if the row does not exist.

******************************************************************

gboolean

list_store_remove_nth_row (GtkListStore

store, gint n)

{

GtkTreeIter iter;

g_return_val_if_fail (GTK_IS_LIST_STORE(store), FALSE);

NULL means the parent is the virtual root node, so the

n-th top-level element is returned in iter, which is

the n-th row in a list store (as a list store only has

top-level elements, and no children)

if (gtk_tree_model_iter_nth_child(GTK_TREE_MODEL(store), &iter, NULL, n))

{

gtk_list_store_remove(store, &iter);

return TRUE;

}

return FALSE;

}

3.7. Removing Multiple Rows

Removing multiple rows at once can be a bit tricky at times, and requires some thought on how to do this best.

For example, it is not possible to traverse a store with gtk_tree_model_foreach, check in the callback function

whether the given row should be removed and then just remove it by calling one of the stores’ remove functions.

This will not work, because the model is changed from within the foreach loop, which might suddenly invalidate

formerly valid tree iters in the foreach function, and thus lead to unpredictable results.

You could traverse the store in a while loop of course, and call gtk_list_store_remove or

gtk_tree_store_remove whenever you want to remove a row, and then just continue if the remove functions

returns TRUE (meaning that the iter is still valid and now points to the row after the row that was removed).

However, this approach will only work with Gtk+-2.2 or later and will not work if you want your programs to

compile and work with Gtk+-2.0 as well, for the reasons outlined above (in Gtk+-2.0 the remove functions did

not set the passed iter to the next valid row). Also, while this approach might be feasable for a list store, it gets a

bit awkward for a tree store.

Here is an example for an alternative approach to removing multiple rows in one go (here we want to remove all

rows from the store that contain persons that have been born after 1980, but it could just as well be all selected

rows or some other criterion):

******************************************************************

Removing multiple rows in one go

******************************************************************

...

gboolean

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