ListModel#
- class ListModel(*args, **kwargs)#
Implementations: ListStore
GListModel
is an interface that represents a mutable list of
Object
. Its main intention is as a model for various widgets
in user interfaces, such as list views, but it can also be used as a
convenient method of returning lists of data, with support for
updates.
Each object in the list may also report changes in itself via some
mechanism (normally the notify
signal). Taken
together with the items_changed
signal, this provides
for a list that can change its membership, and in which the members can
change their individual properties.
A good example would be the list of visible wireless network access points, where each access point can report dynamic properties such as signal strength.
It is important to note that the GListModel
itself does not report
changes to the individual items. It only reports changes to the list
membership. If you want to observe changes to the objects themselves
then you need to connect signals to the objects that you are
interested in.
All items in a GListModel
are of (or derived from) the same type.
get_item_type
returns that type. The type may be an
interface, in which case all objects in the list must implement it.
The semantics are close to that of an array:
get_n_items
returns the number of items in the list
and get_item
returns an item at a (0-based) position.
In order to allow implementations to calculate the list length lazily,
you can also iterate over items: starting from 0, repeatedly call
get_item
until it returns NULL
.
An implementation may create objects lazily, but must take care to return the same object for a given position until all references to it are gone.
On the other side, a consumer is expected only to hold references on objects that are currently ‘user visible’, in order to facilitate the maximum level of laziness in the implementation of the list and to reduce the required number of signal connections at a given time.
This interface is intended only to be used from a single thread. The
thread in which it is appropriate to use it depends on the particular
implementation, but typically it will be from the thread that owns
the thread-default main context (see
push_thread_default
) in effect at the time that the
model was created.
Over time, it has established itself as good practice for list model
implementations to provide properties item-type
and n-items
to
ease working with them. While it is not required, it is recommended
that implementations provide these two properties. They should return
the values of get_item_type
and
get_n_items
respectively and be defined as such:
properties[PROP_ITEM_TYPE] =
g_param_spec_gtype ("item-type", NULL, NULL, G_TYPE_OBJECT,
G_PARAM_CONSTRUCT_ONLY | G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS);
properties[PROP_N_ITEMS] =
g_param_spec_uint ("n-items", NULL, NULL, 0, G_MAXUINT, 0,
G_PARAM_READABLE | G_PARAM_STATIC_STRINGS);
Methods#
- class ListModel
- get_item(position: int) Object | None #
Get the item at
position
.If
position
is greater than the number of items inlist
,None
is returned.None
is never returned for an index that is smaller than the length of the list.See also:
get_n_items()
Added in version 2.44.
- Parameters:
position – the position of the item to fetch
- get_item_type() type #
Gets the type of the items in
list
.All items returned from
get_item()
are of the type returned by this function, or a subtype, or if the type is an interface, they are an implementation of that interface.The item type of a
ListModel
can not change during the life of the model.Added in version 2.44.
- get_n_items() int #
Gets the number of items in
list
.Depending on the model implementation, calling this function may be less efficient than iterating the list with increasing values for
position
untilget_item()
returnsNone
.Added in version 2.44.
- items_changed(position: int, removed: int, added: int) None #
Emits the
ListModel
::items-changed signal onlist
.This function should only be called by classes implementing
ListModel
. It has to be called after the internal representation oflist
has been updated, because handlers connected to this signal might query the new state of the list.Implementations must only make changes to the model (as visible to its consumer) in places that will not cause problems for that consumer. For models that are driven directly by a write API (such as
ListStore
), changes can be reported in response to uses of that API. For models that represent remote data, changes should only be made from a fresh mainloop dispatch. It is particularly not permitted to make changes in response to a call to theListModel
consumer API.Stated another way: in general, it is assumed that code making a series of accesses to the model via the API, without returning to the mainloop, and without calling other code, will continue to view the same contents of the model.
Added in version 2.44.
- Parameters:
position – the position at which
list
changedremoved – the number of items removed
added – the number of items added
Signals#
Virtual Methods#
- class ListModel
- do_get_item(position: int) Object | None #
Get the item at
position
. Ifposition
is greater than the number of items inlist
,None
is returned.None
is never returned for an index that is smaller than the length of the list. Seeget_n_items()
.The same
Object
instance may not appear more than once in aListModel
.Added in version 2.44.
- Parameters:
position – the position of the item to fetch
- do_get_item_type() type #
Gets the type of the items in
list
.All items returned from
get_item()
are of the type returned by this function, or a subtype, or if the type is an interface, they are an implementation of that interface.The item type of a
ListModel
can not change during the life of the model.Added in version 2.44.
- do_get_n_items() int #
Gets the number of items in
list
.Depending on the model implementation, calling this function may be less efficient than iterating the list with increasing values for
position
untilget_item()
returnsNone
.Added in version 2.44.