CaffeinatedSingleChildLayout

public protocol CaffeinatedSingleChildLayout

  • Declaration

    Swift

    typealias Subelement = LayoutSubelement

  • Cached values associated with the layout instance.

    If you create a cache for your custom layout, you can use a type alias to define this type as your data storage type. Alternatively, you can refer to the data storage type directly in all the places where you work with the cache.

    See makeCache(subelement:environment:) for more information.

    Declaration

    Swift

    associatedtype Cache = Void

  • Returns the size of the element, given a proposed size constraint and the container’s subelement.

    Implement this method to tell your custom layout container’s parent how much space the container needs for a subelement, given a size constraint. The parent might call this method more than once during a layout pass with different proposed sizes to test the flexibility of the container.

    In Blueprint, parents ultimately choose the size of their children, so the actual size that this container is laid out in may not be a size that was returned from this method.

    For more information, see sizeThatFits(proposal:subelements:environment:cache:).

    Declaration

    Swift

    func sizeThatFits(
    proposal: SizeConstraint,
    subelement: Subelement,
    environment: Environment,
    cache: inout Cache
) -> CGSize

    Parameters

    proposal

    A size constraint for the container. The container’s parent element that calls this method might call the method more than once with different constraints to learn more about the container’s flexibility before choosing a size for placement.
    subelement

    A proxy that represents the element that the container arranges. You can use the proxy to get information about the subelement as you determine how much space the container needs to display it.
    environment

    The environment of the container. You can use properties from the environment when calculating the size of this container, as long as you adhere to the sizing rules.
    cache

    Optional storage for calculated data that you can share among the methods of your custom layout container. See makeCache(subelement:environment:) for details.

    Return Value

    A size that indicates how much space the container needs to arrange its subelement.

  • Assigns a position to the layout’s subelement.

    Blueprint calls your implementation of this method to tell your custom layout container to place its subelement. From this method, call the place(at:anchor:size:) method on subelement to tell the subelement where to appear in the user interface.

    You can also update the attributes property to set properties like opacity and transforms on the subelement.

    Be sure that you use computations during placement that are consistent with those in your implementation of other protocol methods for a given set of inputs. For example, if you add spacing during placement, make sure your implementation of sizeThatFits(proposal:subelement:environment:cache:) accounts for the extra space.

    Declaration

    Swift

    func placeSubelement(
    in size: CGSize,
    subelement: Subelement,
    environment: Environment,
    cache: inout Cache
)

    Parameters

    size

    The region that the container’s parent allocates to the container. Place the container’s subelement within the region. The size of this region may not match any size that was returned from a call to sizeThatFits(proposal:subelement:environment:cache:).
    subelement

    A proxy that represents the element that the container arranges. Use the proxy to get information about the subelement and to tell the subelement where to appear.
    environment

    The environment of this container. You can use properties from the environment to vary the placement of the subelement.
    cache

    Optional storage for calculated data that you can share among the methods of your custom layout container. See makeCache(subelement:environment:) for details.

  • Creates and initializes a cache for a layout instance.

    You can optionally use a cache to preserve calculated values across calls to a layout container’s methods. Many layout types don’t need a cache, because Blueprint automatically caches the results of calls into layout methods, such as sizeThatFits(_:). Rely on the protocol’s default implementation of this method if you don’t need a cache.

    However you might find a cache useful when the layout container repeats complex intermediate calculations across calls to sizeThatFits(proposal:subelement:environment:cache:) and placeSubelement(in:subelement:environment:cache:). You might be able to improve performance by calculating values once and storing them in a cache.

    Note

    A cache’s lifetime is limited to a single render pass, so you cannot use it to store values across multiple calls to placeSubelement(in:subelement:environment:cache:). A render pass includes zero, one, or many calls to sizeThatFits(proposal:subelement:environment:cache:), followed by a single call to placeSubelement(in:subelement:environment:cache:).

    Only implement a cache if profiling shows that it improves performance.

    For more information, see makeCache(subelements:environment:).

    Declaration

    Swift

    func makeCache(subelement: Subelement, environment: Environment) -> Cache

    Parameters

    subelement

    A proxy that represent the subelement that the container arranges. You can use the proxy to get information about the subelement as you calculate values to store in the cache.
    environment

    The environment of this container.

    Return Value

    Storage for calculated data that you share among the methods of your custom layout container.