Gtk.TreeModel

Gtk.TreeModel — The tree interface used by Gtk.TreeView

Object Hierarchy:

    GBoxed
    ├── Gtk.TreeIter
    ╰── Gtk.TreePath
    GInterface
    ╰── Gtk.TreeModel

See also:

Gtk.TreeView, Gtk.TreeStore, Gtk.ListStore, [Gtk.TreeView drag-and-drop][gtk3-Gtk.TreeView-drag-and-drop] Gtk.TreeSortable

Functions:

Signals:

  • “row-changed” (tree_model, path, iter, user_data)
  • “row-deleted” (tree_model, path, user_data)
  • “row-has-child-toggled” (tree_model, path, iter, user_data)
  • “row-inserted” (tree_model, path, iter, user_data)

Description:

The Gtk.TreeModel interface defines a generic tree interface for use by the Gtk.TreeView widget. It is an abstract interface, and is designed to be usable with any appropriate data structure. The programmer just has to implement this interface on their own data type for it to be viewable by a Gtk.TreeView widget.

The model is represented as a hierarchical tree of strongly-typed, columned data. In other words, the model can be seen as a tree where every node has different values depending on which column is being queried. The type of data found in a column is determined by using the GType system (ie. GObject.TYPE_INT, GObject.GType(Gtk.Button), GObject.TYPE_POINTER, etc). The types are homogeneous per column across all nodes. It is important to note that this interface only provides a way of examining a model and observing changes. The implementation of each individual model decides how and if changes are made.

In order to make life simpler for programmers who do not need to write their own specialized model, two generic models are provided — the Gtk.TreeStore and the Gtk.ListStore. To use these, the developer simply pushes data into these models as necessary. These models provide the data structure as well as all appropriate tree interfaces. As a result, implementing drag and drop, sorting, and storing data is trivial. For the vast majority of trees and lists, these two models are sufficient.

Models are accessed on a node/column level of granularity. One can query for the value of a model at a certain node and a certain column on that node. There are two structures used to reference a particular node in a model. They are the Gtk.TreePath-struct and the GtkTreeIter-struct (iter is short for iterator). Most of the interface consists of operations on a Gtk.TreeIter-struct.

A path is essentially a potential node. It is a location on a model that may or may not actually correspond to a node on a specific model. The Gtk.TreePath-struct can be converted into either an array of unsigned integers 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.

By contrast, a Gtk.TreeIter-struct is a reference to a specific node on a specific model. It is a generic struct with an integer and three generic pointers. These are filled in by the model in a model-specific way. One can convert a path to an iterator by calling Gtk.TreeModel::get_iter(). These iterators are the primary way of accessing a model and are similar to the iterators used by Gtk.TextBuffer. They are generally statically allocated on the stack and only used for a short time. The model interface defines a set of operations using them for navigating the model.

It is expected that models fill in the iterator with private data.

For example, the Gtk.ListStore model, which is internally a simple linked list, stores a list node in one of the pointers. The Gtk.TreeModelSort stores an array and an offset in two of the pointers. Additionally, there is an integer field. This field is generally filled with a unique stamp per model. This stamp is for catching errors resulting from using invalid iterators with a model.

The lifecycle of an iterator can be a little confusing at first.

Iterators are expected to always be valid for as long as the model is unchanged (and doesn’t emit a signal). The model is considered to own all outstanding iterators and nothing needs to be done to free them from the user’s point of view. Additionally, some models guarantee that an iterator is valid for as long as the node it refers to is valid (most notably the GtkTreeStore and Gtk.ListStore).

Although generally uninteresting, as one always has to allow for the case where iterators do not persist beyond a signal, some very important performance enhancements were made in the sort model.

As a result, the Gtk.TreeModelFlags.ITERS_PERSIST flag was added to indicate this behavior.

To help show some common operation of a model, some examples are provided. The first example shows three ways of getting the iter at easier, the second is much more common, as you often get paths from callbacks.

Acquiring a Gtk.TreeIter-struct
    # Three ways of getting the iter pointing to the location

    iter = model.get_iter_from_string("3:2:5")

    # get the iterator from a path path = gtk_tree_path_new_from_string ("3:2:5");
    iter = model.get_iter(path)

    # walk the tree to find the iterator
    iter = model.iter_nth_child(None, 3)
    parent_iter = iter
    iter = model.iter_nth_child(parent_iter, 2)
    parent_iter = iter
    iter = model.iter_nth_child(parent_iter, 5)

This second example shows a quick way of iterating through a list and getting a string and an integer from each row. The populate_model() function used below is not shown, as it is specific to the Gtk.ListStore. For information on how to write such a function, see the Gtk.ListStore documentation.

Reading data from a Gtk.TreeModel
    # make a new list_store list_store = Gtk.ListStore(str, int)
    # Fill the list store with data populate_model (list_store);
    # Get the first iter in the list, check it is valid and walk
    # through the list, reading each row.

    list_store = Gtk.ListStore(str, int)
    list_store.append(["Oranges", 5])
    list_store.append(["Apples", 3])
    list_store.append(["Bananas", 2])
    list_store.append(["Tomatoes", 4])
    list_store.append(["Cucumber", 1])

    row_count = 0
    iter = list_store.get_iter_first()        
    while iter != None:            
        print(list_store.get_value(iter, 0), list_store.get_value(iter, 1))             
        iter = list_store.iter_next(iter)
        row_count += 1
    print(row_count)

The Gtk.TreeModel interface contains two methods for reference counting: Gtk.TreeModel::ref_node() and GtkTreeModel::unref_node().

These two methods are optional to implement. The reference counting is meant as a way for views to let models know when nodes are being displayed. Gtk.TreeView will take a reference on a node when it is visible, which means the node is either in the toplevel or expanded.

Being displayed does not mean that the node is currently directly visible to the user in the viewport. Based on this reference counting scheme a caching model, for example, can decide whether or not to cache a node based on the reference count. A file-system based model would not want to keep the entire file hierarchy in memory, but just the folders that are currently expanded in every current view.

When working with reference counting, the following rules must be taken into account:

  • Never take a reference on a node without owning a reference on its parent. This means that all parent nodes of a referenced node must be referenced as well.

  • Outstanding references on a deleted node are not released. This is not possible because the node has already been deleted by the time the row-deleted signal is received.

  • Models are not obligated to emit a signal on rows of which none of its siblings are referenced. To phrase this differently, signals are only required for levels in which nodes are referenced. For the root level however, signals must be emitted at all times (however the root level is always referenced when any view is attached).

Function Details:

get_flags()

get_flags (self) -> Gtk.TreeModelFlags

Returns a set of flags supported by this interface. The flags are a bitwise combination of Gtk.TreeModelFlags.The flags supported should not change during the lifetimeof the tree_model.

  • Returns: the flags supported by this interface

get_n_columns()

get_n_columns (self) -> int

Returns the number of columns supported by tree_model.

  • Returns: the number of columns

get_column_type()

get_column_type (self, index_:int) -> GType

Returns the type of the column.

  • Returns: the type of the column

get_iter()

get_iter (self, path:Gtk.TreePath) -> bool, iter:Gtk.TreeIter

Sets iter to a valid iterator pointing to path. If path doesnot exist, iter is set to an invalid iterator and FALSE is returned.

  • Returns: True, if iterwas set

get_path()

get_path (self, iter:Gtk.TreeIter) -> Gtk.TreePath

Returns a newly-created Gtk.TreePath referenced by iter. This path should be freed with `Gtk.TreePath:free()`.

  • Returns: a newly-created Gtk.TreePath

get_value()

get_value (self, iter:Gtk.TreeIter, column:int) -> value:GObject.Value

Initializes and sets value to that at column. When done with value, g_value_unset() needs to be calledto free any allocated memory.

iter_next()

iter_next (self, iter:Gtk.TreeIter) -> bool

Sets iter to point to the node following it at the current level. If there is no next iter, FALSE is returned and iter is setto be invalid.

  • Returns: True if iterhas been changed to the next node

iter_previous()

iter_previous (self, iter:Gtk.TreeIter) -> bool

Sets iter to point to the previous node at the current level. If there is no previous iter, FALSE is returned and iter isset to be invalid.

  • Returns: True if iterhas been changed to the previous node

  • Since: 3.0

iter_has_child()

iter_has_child (self, iter:Gtk.TreeIter) -> bool

Returns True if iter has children, FALSE otherwise.

  • Returns: True if iterhas children

iter_n_children()

iter_n_children (self, iter:Gtk.TreeIter=None) -> int

Returns the number of children that iter has. As a special case, if iter is None, then the numberof toplevel nodes is returned.

  • Returns: the number of children of iter

get_string_from_iter()

get_string_from_iter (self, iter:Gtk.TreeIter) -> str

Generates a string representation of the iter. This string is a “:” separated list of numbers.For example, “4:10:0:3” would be an acceptablereturn value for this string.

  • Returns: a newly-allocated string.Must be freed with g_free().

  • Since: 2.2

ref_node()

ref_node (self, iter:Gtk.TreeIter)

Lets the tree ref the node. This is an optional method for models to implement.To be more specific, models may ignore this call as it existsprimarily for performance reasons. This function is primarily meant as a way for views to letcaching models know when nodes are being displayed (and hence,whether or not to cache that node). Being displayed means a nodeis in an expanded branch, regardless of whether the node is currentlyvisible in the viewport. For example, a file-system based modelwould not want to keep the entire file-hierarchy in memory,just the sections that are currently being displayed byevery current view. A model should be expected to be able to get an iter independentof its reffed state.

unref_node()

unref_node (self, iter:Gtk.TreeIter)

Lets the tree unref the node. This is an optional method for models to implement.To be more specific, models may ignore this call as it existsprimarily for performance reasons. For more information on whatthis means, see Gtk.TreeModel:ref_node(). Please note that nodes that are deleted are not unreffed.

foreach()

foreach (self, func:Gtk.TreeModelForeachFunc, user_data=None)

Calls func on each node in model in a depth-first fashion. If func returns True, then the tree ceases to be walked,and Gtk.TreeModel:foreach() returns.

row_changed()

row_changed (self, path:Gtk.TreePath, iter:Gtk.TreeIter)

Emits the “row-changed” signal on tree_model.

row_inserted()

row_inserted (self, path:Gtk.TreePath, iter:Gtk.TreeIter)

Emits the “row-inserted” signal on tree_model.

row_has_child_toggled()

row_has_child_toggled (self, path:Gtk.TreePath, iter:Gtk.TreeIter)

Emits the “row-has-child-toggled” signal ontree_model. This should be called by models after the childstate of a node changes.

row_deleted()

row_deleted (self, path:Gtk.TreePath)

Emits the “row-deleted” signal on tree_model. This should be called by models after a row has been removed.The location pointed to by path should be the location thatthe row previously was at. It may not be a valid location anymore. Nodes that are deleted are not unreffed, this means that anyoutstanding references on the deleted node should not be released.

rows_reordered()

rows_reordered (self, path:Gtk.TreePath, iter:Gtk.TreeIter=None, new_order:list)

Emits the “rows-reordered” signal on tree_model. This should be called by models when their rows have beenreordered. [skip]

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