PinnableContainer.kt
/*
* Copyright 2022 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.runtime.compositionLocalOf
/**
* Use this composition local to get the [PinnableContainer] handling the current subhierarchy.
*
* It will be not null, for example, when the current content is composed as an item of lazy list.
*/
val LocalPinnableContainer = compositionLocalOf<PinnableContainer?> { null }
/**
* Represents a container which can be pinned when the content of this container is important.
*
* For example, each item of lazy list represents one [PinnableContainer], and if this
* container is pinned, this item will not be disposed when scrolled out of the viewport.
*
* Pinning a currently focused item so the focus is not lost is one of the examples when this
* functionality can be useful.
*
* @see LocalPinnableContainer
*/
@Stable
interface PinnableContainer {
/**
* Allows to pin this container when the associated content is considered important.
*
* For example, if this [PinnableContainer] is an item of lazy list pinning will mean
* this item will not be disposed when scrolled out of the viewport.
*
* Don't forget to call [PinnedHandle.release] when this content is not important anymore.
*/
fun pin(): PinnedHandle
/**
* This is an object returned by [pin] which allows to release the pinning.
*/
@Suppress("NotCloseable")
fun interface PinnedHandle {
/**
* Releases the pin.
*
* For example, if this [PinnableContainer] is an item of lazy list releasing the
* pinning will allow lazy list to stop composing the item when it is not visible.
*/
fun release()
}
}