SlotEditor

Kotlin |Java

open class SlotEditor

kotlin.Any
↳	androidx.compose.SlotEditor

Known Direct Subclasses SlotReader, SlotWriter SlotReader SlotWriter

A gap buffer implementation of the composition slot space. A slot space can be thought of as a custom List<Any?> that optimizes around inserts and removes.

Slots stores slots, groups, and nodes.

Slot - A slot is the primitive base type of the slot space. It is of type Any? and can hold any value. Group - A group is a keyed group of slots. The group counts the number of slots and nodes it contains. Node - A node is a special group that is counted by the containing groups.

All groups and nodes are just grouping of slots and use slots to describe the groups. At the root of a slot space is a group. Groups count the number nodes that are in the group. A node only counts as one node in its group regardless of the number of nodes it contains.

ASIDE: The intent is that groups represent memoized function calls and nodes represent views. For example:

Column {
    Contact(contact = jim)
    Contact(contact = bob)
}

the LinearLayout here would be a node (the linear layout view). The node contains the groups for the child views of the linear layout.

If contact's composition looks like:

@Composable
fun Contact(contact: Contact) {
    Text(text = contact.name)
    Text(text = contact.email)
}

then composing contact into the linear layout would add two views to the linear layout's children. The composition of contact creates groups, one for each text view. The groups for each contact would be able to report that it produces two views (that is the group created for Contact has two nodes). Summing the nodes in the group produces the number of views (as each node corresponds to a view).

If the order of jim and bob change:

Column {
    Contact(contact = bob)
    Contact(contact = jim)
}

the previous result can be reused by moving the views generated bob's group before jim's (or visversa). A composition algorithm could use the key information for each group to determine if theycan be switched. For example, since the first contact's group has two nodes the compositionalgorithm can infer that the beginning of jim's views starts at 2 and contains 2 view. To movejim in front of bob, move the 2 views from offset 2 to offset 0. If contact is immutable, forexample, Contact would only need to be recomposed if the value of jim or bob change.

Summary

Public methods
Any?	get(anchor: Anchor) Get the value at an Anchor
Any?	get(index: Int) Get the value at the index'th slot.
Int	groupSize(index: Int) Return the size of the group at index.
Boolean	isGroup(index: Int) Return true if the slot at index starts a gorup

Properties
Int	current
Int	groupSize Return the number of nodes in the group.
Boolean	isGroup Return true if the current slot starts a group
Boolean	isNode Return true if the current slot starts a node.
Int	nodeIndex Get the number of nodes emitted to the group prior to the current slot.
Int	parentIndex
Int	parentNodes Get the total number of nodes emitted in the group containing the current.
SlotTable	table

Public methods

get

fun get(anchor: Anchor): Any?

Get the value at an Anchor

get

fun get(index: Int): Any?

Get the value at the index'th slot.

groupSize

fun groupSize(index: Int): Int

Return the size of the group at index. isGroup(index) must be true of this will throw.

isGroup

fun isGroup(index: Int): Boolean

Return true if the slot at index starts a gorup

Properties

current

var current: Int

groupSize

val groupSize: Int

Return the number of nodes in the group. isGroup must be true or this will throw.

isGroup

val isGroup: Boolean

Return true if the current slot starts a group

isNode

val isNode: Boolean

Return true if the current slot starts a node. A node is a kind of group so this will return true for isGroup as well.

nodeIndex

val nodeIndex: Int

Get the number of nodes emitted to the group prior to the current slot.

parentIndex

val parentIndex: Int

parentNodes

val parentNodes: Int

Get the total number of nodes emitted in the group containing the current.

table

val table: SlotTable