Struct ItemContainerGenerator 

pub struct ItemContainerGenerator { /* private fields */ }

Generates containers for an ItemsControl.

When creating a container for an item from a VirtualizingPanel, the following process should be followed:

• needs_container should first be called to determine whether the item needs a container. This method will return true if the item should be wrapped in a container control, or false if the item itself can be used as a container.
• If needs_container returns true then the create_container method should be called to create a new container, passing the recycle key returned from needs_container.
• If the panel supports recycling and the recycle key is non-null then the recycle key should be recorded for the container (e.g. in an attached property or the realized container list).
• prepare_item_container method should be called for the container.
• The container should then be added to the panel using VirtualizingPanel::add_internal_child.
• Finally, item_container_prepared should be called.

NOTE: If needs_container in the first step above returns false then the above steps should be carried out a single time: the first time the item is displayed. Otherwise the steps should be carried out each time a new container is realized for an item.

When unrealizing a container, the following process should be followed:

• If needs_container for the item returned false then the item cannot be unrealized or recycled.
• Otherwise, clear_item_container should be called for the container.
• If recycling is supported by the panel and the container then the container should be added to a recycle pool keyed on the recycle key returned from needs_container. It is assumed that recycled containers will not be removed from the panel but instead hidden from view using e.g. container.set_is_visible(false).
• If recycling is not supported then the container should be removed from the panel.

When recycling an unrealized container, the following process should be followed:

• needs_container should be called to determine whether the item needs a container, and if so, the recycle key.
• A container should be taken from the recycle pool keyed on the returned recycle key.
• The container should be made visible.
• prepare_item_container method should be called for the container.
• item_container_prepared should be called.

NOTE: Although this class is similar to that found in other XAML frameworks, here this class only concerns itself with generating and clearing item containers; it does not maintain a record of the currently realized containers, that responsibility is delegated to the items panel.

Implementations

impl ItemContainerGenerator

pub fn needs_container( &self, item: &Option<BoxedValue>, index: i32, ) -> (bool, Option<RecycleKey>)

Determines whether the specified item needs to be wrapped in a container control.

Returns true if the item needs a container; otherwise false if the item can itself be used as a container. The second value is a key that can be used to locate a previously recycled container of the correct type, or None if the item cannot be recycled.

pub fn create_container( &self, item: &Option<BoxedValue>, index: i32, recycle_key: Option<RecycleKey>, ) -> Ref<Control>

Creates a new container control.

Before calling this method, needs_container should be called to determine whether the item itself should be used as a container. After calling this method, prepare_item_container must be called to prepare the container to display the specified item.

If the panel supports recycling then the returned recycle key should be stored alongside the container and when container becomes eligible for recycling the container should be placed in a recycle pool using this key. If the returned recycle key is None then the container cannot be recycled.

pub fn prepare_item_container( &self, container: &Ref<Control>, item: &Option<BoxedValue>, index: i32, )

Prepares the specified element as the container for the corresponding item.

If needs_container is false for an item, then this method must only be called a single time; otherwise this method must be called after the container is created, and each subsequent time the container is recycled to display a new item.

pub fn item_container_prepared( &self, container: &Ref<Control>, item: &Option<BoxedValue>, index: i32, )

Notifies the ItemsControl that a container has been fully prepared to display an item.

This method must be called when a container has been fully prepared and added to the logical and visual trees, but may be called before a layout pass has completed. It must be called regardless of the result of needs_container but if that method returned false then must be called only a single time.

pub fn item_container_index_changed( &self, container: &Ref<Control>, old_index: i32, new_index: i32, )

Called when the index for a container changes due to an insertion or removal in the items collection.

pub fn clear_item_container(&self, container: &Ref<Control>)

Undoes the effects of the prepare_item_container method.

This method must be called when a container is unrealized. The container must have already have been removed from the virtualizing panel’s list of realized containers before this method is called. This method must not be called if needs_container returned false for the item.