/*
* 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.foundation.lazy
import androidx.compose.foundation.ExperimentalFoundationApi
import androidx.compose.foundation.layout.Arrangement
import androidx.compose.foundation.layout.PaddingValues
import androidx.compose.runtime.Composable
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.dp
/**
* Receiver scope which is used by [LazyColumn] and [LazyRow].
*/
interface LazyListScope {
/**
* Adds a single item.
*
* @param content the content of the item
*/
fun item(content: @Composable LazyItemScope.() -> Unit)
/**
* Adds a [count] of items.
*
* @param count the items count
* @param itemContent the content displayed by a single item
*/
fun items(count: Int, itemContent: @Composable LazyItemScope.(index: Int) -> Unit)
/**
* Adds a sticky header item, which will remain pinned even when scrolling after it.
* The header will remain pinned until the next header will take its place.
*
* @sample androidx.compose.foundation.samples.StickyHeaderSample
*
* @param content the content of the header
*/
@ExperimentalFoundationApi
fun stickyHeader(content: @Composable LazyItemScope.() -> Unit)
}
/**
* Adds a list of items.
*
* @param items the data list
* @param itemContent the content displayed by a single item
*/
inline fun <T> LazyListScope.items(
items: List<T>,
crossinline itemContent: @Composable LazyItemScope.(item: T) -> Unit
) = items(items.size) {
itemContent(items[it])
}
/**
* Adds a list of items where the content of an item is aware of its index.
*
* @param items the data list
* @param itemContent the content displayed by a single item
*/
inline fun <T> LazyListScope.itemsIndexed(
items: List<T>,
crossinline itemContent: @Composable LazyItemScope.(index: Int, item: T) -> Unit
) = items(items.size) {
itemContent(it, items[it])
}
/**
* Adds an array of items.
*
* @param items the data array
* @param itemContent the content displayed by a single item
*/
inline fun <T> LazyListScope.items(
items: Array<T>,
crossinline itemContent: @Composable LazyItemScope.(item: T) -> Unit
) = items(items.size) {
itemContent(items[it])
}
/**
* Adds an array of items where the content of an item is aware of its index.
*
* @param items the data array
* @param itemContent the content displayed by a single item
*/
inline fun <T> LazyListScope.itemsIndexed(
items: Array<T>,
crossinline itemContent: @Composable LazyItemScope.(index: Int, item: T) -> Unit
) = items(items.size) {
itemContent(it, items[it])
}
internal class LazyListScopeImpl : LazyListScope {
private val intervals = IntervalList<LazyItemScope.(Int) -> (@Composable () -> Unit)>()
val totalSize get() = intervals.totalSize
var headersIndexes: MutableList<Int>? = null
private set
fun contentFor(index: Int, scope: LazyItemScope): @Composable () -> Unit {
val interval = intervals.intervalForIndex(index)
val localIntervalIndex = index - interval.startIndex
return interval.content(scope, localIntervalIndex)
}
override fun items(count: Int, itemContent: @Composable LazyItemScope.(index: Int) -> Unit) {
intervals.add(count) { index ->
@Composable { itemContent(index) }
}
}
override fun item(content: @Composable LazyItemScope.() -> Unit) {
intervals.add(1) { @Composable { content() } }
}
@ExperimentalFoundationApi
override fun stickyHeader(content: @Composable LazyItemScope.() -> Unit) {
val headersIndexes = headersIndexes ?: mutableListOf<Int>().also {
headersIndexes = it
}
headersIndexes.add(totalSize)
item(content)
}
}
/**
* The horizontally scrolling list that only composes and lays out the currently visible items.
* The [content] block defines a DSL which allows you to emit items of different types. For
* example you can use [LazyListScope.item] to add a single item and [LazyListScope.items] to add
* a list of items.
*
* @sample androidx.compose.foundation.samples.LazyRowSample
*
* @param modifier the modifier to apply to this layout
* @param state the state object to be used to control or observe the list's state
* @param contentPadding a padding around the whole content. This will add padding for the
* content after it has been clipped, which is not possible via [modifier] param. You can use it
* to add a padding before the first item or after the last one. If you want to add a spacing
* between each item use [horizontalArrangement].
* @param reverseLayout reverse the direction of scrolling and layout, when `true` items will be
* composed from the end to the start and [LazyListState.firstVisibleItemIndex] == 0 will mean
* the first item is located at the end.
* @param horizontalArrangement The horizontal arrangement of the layout's children. This allows
* to add a spacing between items and specify the arrangement of the items when we have not enough
* of them to fill the whole minimum size.
* @param verticalAlignment the vertical alignment applied to the items
* @param content a block which describes the content. Inside this block you can use methods like
* [LazyListScope.item] to add a single item or [LazyListScope.items] to add a list of items.
*/
@Composable
fun LazyRow(
modifier: Modifier = Modifier,
state: LazyListState = rememberLazyListState(),
contentPadding: PaddingValues = PaddingValues(0.dp),
reverseLayout: Boolean = false,
horizontalArrangement: Arrangement.Horizontal =
if (!reverseLayout) Arrangement.Start else Arrangement.End,
verticalAlignment: Alignment.Vertical = Alignment.Top,
content: LazyListScope.() -> Unit
) {
val scope = LazyListScopeImpl()
scope.apply(content)
LazyList(
itemsCount = scope.totalSize,
modifier = modifier,
state = state,
contentPadding = contentPadding,
verticalAlignment = verticalAlignment,
horizontalArrangement = horizontalArrangement,
isVertical = false,
reverseLayout = reverseLayout,
headerIndexes = scope.headersIndexes ?: emptyList()
) { index ->
scope.contentFor(index, this)
}
}
/**
* The vertically scrolling list that only composes and lays out the currently visible items.
* The [content] block defines a DSL which allows you to emit items of different types. For
* example you can use [LazyListScope.item] to add a single item and [LazyListScope.items] to add
* a list of items.
*
* @sample androidx.compose.foundation.samples.LazyColumnSample
*
* @param modifier the modifier to apply to this layout.
* @param state the state object to be used to control or observe the list's state.
* @param contentPadding a padding around the whole content. This will add padding for the.
* content after it has been clipped, which is not possible via [modifier] param. You can use it
* to add a padding before the first item or after the last one. If you want to add a spacing
* between each item use [verticalArrangement].
* @param reverseLayout reverse the direction of scrolling and layout, when `true` items will be
* composed from the bottom to the top and [LazyListState.firstVisibleItemIndex] == 0 will mean
* we scrolled to the bottom.
* @param verticalArrangement The vertical arrangement of the layout's children. This allows
* to add a spacing between items and specify the arrangement of the items when we have not enough
* of them to fill the whole minimum size.
* @param horizontalAlignment the horizontal alignment applied to the items.
* @param content a block which describes the content. Inside this block you can use methods like
* [LazyListScope.item] to add a single item or [LazyListScope.items] to add a list of items.
*/
@Composable
fun LazyColumn(
modifier: Modifier = Modifier,
state: LazyListState = rememberLazyListState(),
contentPadding: PaddingValues = PaddingValues(0.dp),
reverseLayout: Boolean = false,
verticalArrangement: Arrangement.Vertical =
if (!reverseLayout) Arrangement.Top else Arrangement.Bottom,
horizontalAlignment: Alignment.Horizontal = Alignment.Start,
content: LazyListScope.() -> Unit
) {
val scope = LazyListScopeImpl()
scope.apply(content)
LazyList(
itemsCount = scope.totalSize,
modifier = modifier,
state = state,
contentPadding = contentPadding,
horizontalAlignment = horizontalAlignment,
verticalArrangement = verticalArrangement,
isVertical = true,
reverseLayout = reverseLayout,
headerIndexes = scope.headersIndexes ?: emptyList()
) { index ->
scope.contentFor(index, this)
}
}