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.Immutable
import androidx.compose.runtime.Stable
import androidx.compose.ui.Modifier
import androidx.compose.ui.platform.InspectorInfo
import androidx.compose.ui.platform.InspectorValueInfo
import androidx.compose.ui.platform.debugInspectorInfo
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(
LayoutId(
layoutId = layoutId,
inspectorInfo = debugInspectorInfo {
name = "layoutId"
value = layoutId
}
)
)
/**
* A [ParentDataModifier] 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.
*/
@Immutable
private class LayoutId(
override val layoutId: Any,
inspectorInfo: InspectorInfo.() -> Unit
) : ParentDataModifier, LayoutIdParentData, InspectorValueInfo(inspectorInfo) {
override fun Density.modifyParentData(parentData: Any?): Any? {
return this@LayoutId
}
override fun hashCode(): Int =
layoutId.hashCode()
override fun equals(other: Any?): Boolean {
if (this === other) return true
val otherModifier = other as? LayoutId ?: return false
return layoutId == otherModifier.layoutId
}
override fun toString(): String =
"LayoutId(id=$layoutId)"
}
/**
* 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