Tree and List Widgets

=====================

A :class:`Gtk.TreeView` and its associated widgets are an extremely powerful way

of displaying data. They are used in conjunction with a :class:`Gtk.ListStore`

or :class:`Gtk.TreeStore` and provide a way of displaying and manipulating data

in many ways, including:

* Automatically updates when data added, removed or edited

* Drag and drop support

* Sorting of data

* Support embedding widgets such as check boxes, progress bars, etc.

* Reorderable and resizable columns

* Filtering of data

With the power and flexibility of a :class:`Gtk.TreeView` comes complexity. It

is often difficult for beginner developers to be able to utilize correctly due

to the number of methods which are required.

The Model

---------

Each :class:`Gtk.TreeView` has an associated :class:`Gtk.TreeModel`, which

contains the data displayed by the TreeView. Each :class:`Gtk.TreeModel` can be

used by more than one :class:`Gtk.TreeView`. For instance, this allows the same

underlying data to be displayed and edited in 2 different ways at the same time.

Or the 2 Views might display different columns from the same Model data, in the

same way that 2 SQL queries (or "views") might show different fields from the

same database table.

Although you can theoretically implement your own Model, you will normally use

either the :class:`Gtk.ListStore` or :class:`Gtk.TreeStore` model classes.

:class:`Gtk.ListStore` contains simple rows of data, and each row has no children,

whereas :class:`Gtk.TreeStore` contains rows of data, and each row may have child

rows.

When constructing a model you have to specify the data types for each column the

model holds.

.. code-block:: python

store = Gtk.ListStore(str, str, float)

This creates a list store with three columns, two string columns, and a float

column.

Adding data to the model is done using :meth:`Gtk.ListStore.append` or

:meth:`Gtk.TreeStore.append`, depending upon which sort of model was created.

.. code-block:: python

treeiter = store.append(["The Art of Computer Programming",

"Donald E. Knuth", 25.46])

Both methods return a :class:`Gtk.TreeIter` instance, which points to the location

of the newly inserted row. You can retrieve a :class:`Gtk.TreeIter` by calling

:meth:`Gtk.TreeModel.get_iter`.

Once, data has been inserted you can retrieve or modify data using the tree iter

and column index.

.. code-block:: python

print store[treeiter][2] # Prints value of third column

store[treeiter][2] = 42.15

As with Python's built-in :class:`list` object you can use :func:`len` to get the number

of rows and use slices to retrieve or set values.

.. code-block:: python

# Print number of rows

print len(store)

# Print all but first column

print store[treeiter][1:]

# Print last column

print store[treeiter][-1]

# Set first two columns

store[treeiter][:2] = ["Donald Ervin Knuth", 41.99]

Iterating over all rows of a tree model is very simple as well.

.. code-block:: python

for row in store:

# Print values of all columns

print row[:]

Keep in mind, that if you use :class:`Gtk.TreeStore`, the above code will only

iterate over the rows of the top level, but not the children of the nodes.

To iterate over all rows and its children, use the ``print_tree_store`` function.

.. code-block:: python

def print_tree_store(store):

rootiter = store.get_iter_first()

print_rows(store, rootiter, "")

def print_rows(store, treeiter, indent):

while treeiter != None:

print indent + str(store[treeiter][:])

if store.iter_has_child(treeiter):

childiter = store.iter_children(treeiter)

print_rows(store, childiter, indent + "\t")

treeiter = store.iter_next(treeiter)

Apart from accessing values stored in a :class:`Gtk.TreeModel` with the list-like

method mentioned above, it is also possible to

either use :class:`Gtk.TreeIter` or :class:`Gtk.TreePath` instances. Both reference

a particular row in a tree model.

One can convert a path to an iterator by calling :meth:`Gtk.TreeModel.get_iter`.

As :class:`Gtk.ListStore` contains only one level,

i.e. nodes do not have any child nodes, a path is essentially the index of the row

you want to access.

.. code-block:: python

# Get path pointing to 6th row in list store

path = Gtk.TreePath(5)

treeiter = liststore.get_iter(path)

# Get value at 2nd column

value = liststore.get_value(treeiter, 1)

In the case of :class:`Gtk.TreeStore`, a path is a list of indexes or a string.

The string form is a list of numbers separated by a colon. Each number refers to

the offset at that level. Thus, the path "0" refers to the root node and the

path "2:4" refers to the fifth child of the third node.

.. code-block:: python

# Get path pointing to 5th child of 3rd row in tree store

path = Gtk.TreePath([2, 4])

treeiter = treestore.get_iter(path)

# Get value at 2nd column

value = treestore.get_value(treeiter, 1)

Instances of :class:`Gtk.TreePath` can be accessed like lists, i.e.

``len(treepath)`` returns the depth of the item ``treepath`` is pointing to,

and ``treepath[i]`` returns the child's index on the *i*-th level.

The View

--------

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 :class:`Gtk.TreeView` is not a difficult matter. It needs a

:class:`Gtk.TreeModel` to know where to retrieve its data from, either by

passing it to the :class:`Gtk.TreeView` constructor, or by calling

:meth:`Gtk.TreeView.set_model`.

.. code-block:: python

tree = Gtk.TreeView(store)

Once the :class:`Gtk.TreeView` widget has a model, it will need to know how to

display the model. It does this with columns and cell renderers.

Cell renderers are used to draw the data in the tree model in a way. There are a

number of cell renderers that come with GTK+, for instance

:class:`Gtk.CellRendererText`, :class:`Gtk.CellRendererPixbuf` and

:class:`Gtk.CellRendererToggle`.

In addition, it is relatively easy to write a custom renderer yourself.

A :class:`Gtk.TreeViewColumn` is the object that :class:`Gtk.TreeView` 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.

.. code-block:: python

renderer = Gtk.CellRendererText()

column = Gtk.TreeViewColumn("Title", renderer, text=0)

tree.append_column(column)

To render more than one model column in a view column, you need to create a

:class:`Gtk.TreeViewColumn` instance and use :meth:`Gtk.TreeViewColumn.pack_start`

to add the model columns to it.

.. code-block:: python

column = Gtk.TreeViewColumn("Title and Author")

title = Gtk.CellRendererText()

author = Gtk.CellRendererText()

column.pack_start(title, True)

column.pack_start(author, True)

column.add_attribute(title, "text", 0)

column.add_attribute(author, "text", 1)

tree.append_column(column)

The Selection

-------------

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.

.. code-block:: python

select = tree.get_selection()

select.connect("changed", on_tree_selection_changed)

Then to retrieve data for the row selected:

.. code-block:: python

def on_tree_selection_changed(selection):

model, treeiter = selection.get_selected()

if treeiter != None:

print "You selected", model[treeiter][0]

You can control what selections are allowed by calling

:meth:`Gtk.TreeSelection.set_mode`.

:meth:`Gtk.TreeSelection.get_selected` does not work if the selection mode is

set to :attr:`Gtk.SelectionMode.MULTIPLE`, use

:meth:`Gtk.TreeSelection.get_selected_rows` instead.

Sorting

-------

Sorting is an important feature for tree views and is supported by the standard tree models (:class:`Gtk.TreeStore` and :class:`Gtk.ListStore`), which implement the :class:`Gtk.TreeSortable` interface.

Sorting by clicking on columns

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

A column of a :class:`Gtk.TreeView` can easily made sortable with a call to :meth:`Gtk.TreeViewColumn.set_sort_column_id`.

Afterwards the column can be sorted by clicking on its header.

First we need a simple :class:`Gtk.TreeView` and a :class:`Gtk.ListStore` as a model.

.. code-block:: python

model = Gtk.ListStore(str)

model.append(["Benjamin"])

model.append(["Charles"])

model.append(["alfred"])

model.append(["Alfred"])

model.append(["David"])

model.append(["charles"])

model.append(["david"])

model.append(["benjamin"])

treeView = Gtk.TreeView(model)

cellRenderer = Gtk.CellRendererText()

column = Gtk.TreeViewColumn("Title", renderer, text=0)

The next step is to enable sorting. Note that the *column_id* (``0`` in the example) refers to the column of the model and **not** to the TreeView's column.

.. code-block:: python

column.set_sort_column_id(0)

Setting a custom sort function

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

It is also possible to set a custom comparison function in order to change the sorting behaviour.

As an example we will create a comparison function that sorts case-sensitive.

In the example above the sorted list looked like::

alfred

Alfred

benjamin

Benjamin

charles

Charles

david

David

The case-sensitive sorted list will look like::

Alfred

Benjamin

Charles

David

alfred

benjamin

charles

david

First of all a comparison function is needed.

This function gets two rows and has to return a negative integer if the first one should come before the second one, zero if they are equal and a positive integer if the second one should come before the second one.

.. code-block:: python

def compare(model, row1, row2, user_data):

sort_column, _ = model.get_sort_column_id()

value1 = model.get_value(row1, sort_column)

value2 = model.get_value(row2, sort_column)

if value1 < value2:

return -1

elif value1 == value2:

return 0

else:

return 1

Then the sort function has to be set by :meth:`Gtk.TreeSortable.set_sort_func`.

.. code-block:: python

model.set_sort_func(0, compare, None)