LayoutId.kt
/*
* Copyright 2020 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.layout
import androidx.compose.runtime.Stable
import androidx.compose.ui.Modifier
import androidx.compose.ui.node.ModifierNodeElement
import androidx.compose.ui.node.ParentDataModifierNode
import androidx.compose.ui.platform.InspectorInfo
import androidx.compose.ui.unit.Density
/**
* Tag the element with [layoutId] to identify the element within its parent.
*
* Example usage:
* @sample androidx.compose.ui.samples.LayoutTagChildrenUsage
*/
@Stable
fun Modifier.layoutId(layoutId: Any) = this then LayoutIdModifierElement(layoutId = layoutId)
private data class LayoutIdModifierElement(
private val layoutId: Any
) : ModifierNodeElement<LayoutIdModifier>() {
override fun create() = LayoutIdModifier(layoutId)
override fun update(node: LayoutIdModifier): LayoutIdModifier = node.also {
it.layoutId = layoutId
}
override fun InspectorInfo.inspectableProperties() {
name = "layoutId"
value = layoutId
}
}
/**
* A [ParentDataModifierNode] which tags the target with the given [id][layoutId]. The provided tag
* will act as parent data, and can be used for example by parent layouts to associate
* composable children to [Measurable]s when doing layout, as shown below.
*/
private class LayoutIdModifier(
layoutId: Any,
) : ParentDataModifierNode, LayoutIdParentData, Modifier.Node() {
override var layoutId: Any = layoutId
internal set
override fun Density.modifyParentData(parentData: Any?): Any? {
return this@LayoutIdModifier
}
}
/**
* Can be implemented by values used as parent data to make them usable as tags.
* If a parent data value implements this interface, it can then be returned when querying
* [Measurable.layoutId] for the corresponding child.
*/
interface LayoutIdParentData {
val layoutId: Any
}
/**
* Retrieves the tag associated to a composable with the [Modifier.layoutId] modifier.
* For a parent data value to be returned by this property when not using the [Modifier.layoutId]
* modifier, the parent data value should implement the [LayoutIdParentData] interface.
*
* Example usage:
* @sample androidx.compose.ui.samples.LayoutTagChildrenUsage
*/
val Measurable.layoutId: Any?
get() = (parentData as? LayoutIdParentData)?.layoutId