Struct gio::ListModel

source ·
#[repr(transparent)]
pub struct ListModel { /* private fields */ }
Expand description

ListModel is an interface that represents a mutable list of GObjects. 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 signal::glib::Object::notify signal). Taken together with the signal::ListModel::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 ListModel 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 ListModel are of (or derived from) the same type. ListModelExt::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: ListModelExt::n_items() returns the number of items in the list and g_list_model_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 g_list_model_get_item() until it returns None.

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][g-main-context-push-thread-default] in effect at the time that the model was created.

Over time, it has established itself as good practice for listmodel 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 ListModelExt::item_type() and ListModelExt::n_items() respectively and be defined as such:

⚠️ The following code is in C ⚠️

properties[PROP_ITEM_TYPE] =
  g_param_spec_gtype ("item-type", "", "", G_TYPE_OBJECT,
                      G_PARAM_CONSTRUCT_ONLY | G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS);
properties[PROP_N_ITEMS] =
  g_param_spec_uint ("n-items", "", "", 0, G_MAXUINT, 0,
                     G_PARAM_READABLE | G_PARAM_STATIC_STRINGS);

Implements

ListModelExt, ListModelExtManual

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