/*
* Copyright 2019 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.compose.ui
import androidx.compose.runtime.Stable
import androidx.compose.ui.internal.JvmDefaultWithCompatibility
import androidx.compose.ui.node.DelegatableNode
import androidx.compose.ui.node.NodeCoordinator
import androidx.compose.ui.node.NodeKind
import androidx.compose.ui.node.requireOwner
/**
* An ordered, immutable collection of [modifier elements][Modifier.Element] that decorate or add
* behavior to Compose UI elements. For example, backgrounds, padding and click event listeners
* decorate or add behavior to rows, text or buttons.
*
* @sample androidx.compose.ui.samples.ModifierUsageSample
*
* Modifier implementations should offer a fluent factory extension function on [Modifier] for
* creating combined modifiers by starting from existing modifiers:
*
* @sample androidx.compose.ui.samples.ModifierFactorySample
*
* Modifier elements may be combined using [then]. Order is significant; modifier elements that
* appear first will be applied first.
*
* Composables that accept a [Modifier] as a parameter to be applied to the whole component
* represented by the composable function should name the parameter `modifier` and
* assign the parameter a default value of [Modifier]. It should appear as the first
* optional parameter in the parameter list; after all required parameters (except for trailing
* lambda parameters) but before any other parameters with default values. Any default modifiers
* desired by a composable function should come after the `modifier` parameter's value in the
* composable function's implementation, keeping [Modifier] as the default parameter value.
* For example:
*
* @sample androidx.compose.ui.samples.ModifierParameterSample
*
* The pattern above allows default modifiers to still be applied as part of the chain
* if a caller also supplies unrelated modifiers.
*
* Composables that accept modifiers to be applied to a specific subcomponent `foo`
* should name the parameter `fooModifier` and follow the same guidelines above for default values
* and behavior. Subcomponent modifiers should be grouped together and follow the parent
* composable's modifier. For example:
*
* @sample androidx.compose.ui.samples.SubcomponentModifierSample
*/
@Suppress("ModifierFactoryExtensionFunction")
@Stable
@JvmDefaultWithCompatibility
interface Modifier {
/**
* Accumulates a value starting with [initial] and applying [operation] to the current value
* and each element from outside in.
*
* Elements wrap one another in a chain from left to right; an [Element] that appears to the
* left of another in a `+` expression or in [operation]'s parameter order affects all
* of the elements that appear after it. [foldIn] may be used to accumulate a value starting
* from the parent or head of the modifier chain to the final wrapped child.
*/
fun <R> foldIn(initial: R, operation: (R, Element) -> R): R
/**
* Accumulates a value starting with [initial] and applying [operation] to the current value
* and each element from inside out.
*
* Elements wrap one another in a chain from left to right; an [Element] that appears to the
* left of another in a `+` expression or in [operation]'s parameter order affects all
* of the elements that appear after it. [foldOut] may be used to accumulate a value starting
* from the child or tail of the modifier chain up to the parent or head of the chain.
*/
fun <R> foldOut(initial: R, operation: (Element, R) -> R): R
/**
* Returns `true` if [predicate] returns true for any [Element] in this [Modifier].
*/
fun any(predicate: (Element) -> Boolean): Boolean
/**
* Returns `true` if [predicate] returns true for all [Element]s in this [Modifier] or if
* this [Modifier] contains no [Element]s.
*/
fun all(predicate: (Element) -> Boolean): Boolean
/**
* Concatenates this modifier with another.
*
* Returns a [Modifier] representing this modifier followed by [other] in sequence.
*/
infix fun then(other: Modifier): Modifier =
if (other === Modifier) this else CombinedModifier(this, other)
/**
* A single element contained within a [Modifier] chain.
*/
@JvmDefaultWithCompatibility
interface Element : Modifier {
override fun <R> foldIn(initial: R, operation: (R, Element) -> R): R =
operation(initial, this)
override fun <R> foldOut(initial: R, operation: (Element, R) -> R): R =
operation(this, initial)
override fun any(predicate: (Element) -> Boolean): Boolean = predicate(this)
override fun all(predicate: (Element) -> Boolean): Boolean = predicate(this)
}
/**
* The longer-lived object that is created for each [Modifier.Element] applied to a
* [androidx.compose.ui.layout.Layout]. Most [Modifier.Node] implementations will have a
* corresponding "Modifier Factory" extension method on Modifier that will allow them to be used
* indirectly, without ever implementing a [Modifier.Node] subclass directly. In some cases it
* may be useful to define a custom [Modifier.Node] subclass in order to efficiently implement
* some collection of behaviors that requires maintaining state over time and over many
* recompositions where the various provided Modifier factories are not sufficient.
*
* When a [Modifier] is set on a [androidx.compose.ui.layout.Layout], each [Modifier.Element]
* contained in that linked list will result in a corresponding [Modifier.Node] instance in a
* matching linked list of [Modifier.Node]s that the [androidx.compose.ui.layout.Layout] will
* hold on to. As subsequent [Modifier] chains get set on the
* [androidx.compose.ui.layout.Layout], the linked list of [Modifier.Node]s will be diffed and
* updated as appropriate, even though the [Modifier] instance might be completely new. As a
* result, the lifetime of a [Modifier.Node] is the intersection of the lifetime of the
* [androidx.compose.ui.layout.Layout] that it lives on and a corresponding [Modifier.Element]
* being present in the [androidx.compose.ui.layout.Layout]'s [Modifier].
*
* If one creates a subclass of [Modifier.Node], it is expected that it will implement one or
* more interfaces that interact with the various Compose UI subsystems. To use the
* [Modifier.Node] subclass, it is expected that it will be instantiated by adding a
* [androidx.compose.ui.node.ModifierNodeElement] to a [Modifier] chain.
*
* @see androidx.compose.ui.node.modifierElementOf
* @see androidx.compose.ui.node.ModifierNodeElement
* @see androidx.compose.ui.node.DelegatableNode
* @see androidx.compose.ui.node.DelegatingNode
* @see androidx.compose.ui.node.LayoutModifierNode
* @see androidx.compose.ui.node.DrawModifierNode
* @see androidx.compose.ui.node.SemanticsModifierNode
* @see androidx.compose.ui.node.PointerInputModifierNode
* @see androidx.compose.ui.modifier.ModifierLocalNode
* @see androidx.compose.ui.node.ParentDataModifierNode
* @see androidx.compose.ui.node.LayoutAwareModifierNode
* @see androidx.compose.ui.node.GlobalPositionAwareModifierNode
* @see androidx.compose.ui.node.IntermediateLayoutModifierNode
*/
@ExperimentalComposeUiApi
abstract class Node : DelegatableNode {
@Suppress("LeakingThis")
final override var node: Node = this
private set
internal var kindSet: Int = 0
// NOTE: We use an aggregate mask that or's all of the type masks of the children of the
// chain so that we can quickly prune a subtree. This INCLUDES the kindSet of this node
// as well
internal var aggregateChildKindSet: Int = 0
internal var parent: Node? = null
internal var child: Node? = null
internal var coordinator: NodeCoordinator? = null
private set
/**
* Indicates that the node is attached and part of the tree. This will get set to true
* right before [onAttach] is called, and set to false right after [onDetach] is called.
*
* A Node will never be attached more than once.
*
* @see onAttach
* @see onDetach
*/
var isAttached: Boolean = false
private set
internal open fun updateCoordinator(coordinator: NodeCoordinator?) {
this.coordinator = coordinator
}
@Suppress("NOTHING_TO_INLINE")
internal inline fun isKind(kind: NodeKind<*>) = kindSet and kind.mask != 0
internal fun attach() {
check(!isAttached)
check(coordinator != null)
isAttached = true
onAttach()
// TODO(lmr): run side effects?
}
internal fun detach() {
check(isAttached)
check(coordinator != null)
onDetach()
isAttached = false
// coordinator = null
// TODO(lmr): cancel jobs / side effects?
}
/**
* When called, `node` is guaranteed to be non-null. You can call sideEffect,
* coroutineScope, etc.
*/
open fun onAttach() {}
/**
* This should be called right before the node gets removed from the list, so you should
* still be able to traverse inside of this method. Ideally we would not allow you to
* trigger side effects here.
*/
open fun onDetach() {}
/**
* This can be called to register [effect] as a function to be executed after all of the
* changes to the tree are applied.
*
* This API can only be called if the node [isAttached].
*/
fun sideEffect(effect: () -> Unit) {
requireOwner().registerOnEndApplyChangesListener(effect)
}
internal fun setAsDelegateTo(owner: Node) {
node = owner
}
}
/**
* The companion object `Modifier` is the empty, default, or starter [Modifier]
* that contains no [elements][Element]. Use it to create a new [Modifier] using
* modifier extension factory functions:
*
* @sample androidx.compose.ui.samples.ModifierUsageSample
*
* or as the default value for [Modifier] parameters:
*
* @sample androidx.compose.ui.samples.ModifierParameterSample
*/
// The companion object implements `Modifier` so that it may be used as the start of a
// modifier extension factory expression.
companion object : Modifier {
override fun <R> foldIn(initial: R, operation: (R, Element) -> R): R = initial
override fun <R> foldOut(initial: R, operation: (Element, R) -> R): R = initial
override fun any(predicate: (Element) -> Boolean): Boolean = false
override fun all(predicate: (Element) -> Boolean): Boolean = true
override infix fun then(other: Modifier): Modifier = other
override fun toString() = "Modifier"
}
}
/**
* A node in a [Modifier] chain. A CombinedModifier always contains at least two elements;
* a Modifier [outer] that wraps around the Modifier [inner].
*/
class CombinedModifier(
internal val outer: Modifier,
internal val inner: Modifier
) : Modifier {
override fun <R> foldIn(initial: R, operation: (R, Modifier.Element) -> R): R =
inner.foldIn(outer.foldIn(initial, operation), operation)
override fun <R> foldOut(initial: R, operation: (Modifier.Element, R) -> R): R =
outer.foldOut(inner.foldOut(initial, operation), operation)
override fun any(predicate: (Modifier.Element) -> Boolean): Boolean =
outer.any(predicate) || inner.any(predicate)
override fun all(predicate: (Modifier.Element) -> Boolean): Boolean =
outer.all(predicate) && inner.all(predicate)
override fun equals(other: Any?): Boolean =
other is CombinedModifier && outer == other.outer && inner == other.inner
override fun hashCode(): Int = outer.hashCode() + 31 * inner.hashCode()
override fun toString() = "[" + foldIn("") { acc, element ->
if (acc.isEmpty()) element.toString() else "$acc, $element"
} + "]"
}