LazyLayoutItemProvider.kt
/*
* Copyright 2021 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.foundation.lazy.layout
import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.runtime.Composable
import androidx.compose.runtime.Stable
/**
* Provides all the needed info about the items which could be later composed and displayed as
* children or [LazyLayout].
*/
@Stable
@ExperimentalFoundationApi
interface LazyLayoutItemProvider {
/**
* The total number of items in the lazy layout (visible or not).
*/
val itemCount: Int
/**
* The item for the given [index].
*/
@Composable
fun Item(index: Int)
/**
* Returns the content type for the item on this index. It is used to improve the item
* compositions reusing efficiency. Note that null is a valid type and items of such
* type will be considered compatible.
*/
fun getContentType(index: Int): Any? = null
/**
* Returns the key for the item on this index.
*
* @see getDefaultLazyLayoutKey which you can use if the user didn't provide a key.
*/
fun getKey(index: Int): Any = getDefaultLazyLayoutKey(index)
/**
* Contains the mapping between the key and the index. It could contain not all the items of
* the list as an optimization or be empty if user didn't provide a custom key-index mapping.
*/
val keyToIndexMap: Map<Any, Int> get() = emptyMap()
}
/**
* This creates an object meeting following requirements:
* 1) Objects created for the same index are equals and never equals for different indexes.
* 2) This class is saveable via a default SaveableStateRegistry on the platform.
* 3) This objects can't be equals to any object which could be provided by a user as a custom key.
*/
@ExperimentalFoundationApi
expect fun getDefaultLazyLayoutKey(index: Int): Any