| /* |
| * 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 list of items and their content to the scope. |
| * |
| * @param items the data list |
| * @param itemContent the content displayed by a single item |
| */ |
| fun <T> items( |
| items: List<T>, |
| itemContent: @Composable LazyItemScope.(item: T) -> Unit |
| ) |
| |
| /** |
| * Adds a single item to the scope. |
| * |
| * @param content the content of the item |
| */ |
| fun item(content: @Composable LazyItemScope.() -> Unit) |
| |
| /** |
| * Adds a list of items to the scope 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 |
| */ |
| fun <T> itemsIndexed( |
| items: List<T>, |
| itemContent: @Composable LazyItemScope.(index: Int, item: T) -> 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) |
| } |
| |
| 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 <T> items( |
| items: List<T>, |
| itemContent: @Composable LazyItemScope.(item: T) -> Unit |
| ) { |
| intervals.add(items.size) { index -> |
| val item = items[index] |
| @Composable { itemContent(item) } |
| } |
| } |
| |
| override fun item(content: @Composable LazyItemScope.() -> Unit) { |
| intervals.add(1) { @Composable { content() } } |
| } |
| |
| override fun <T> itemsIndexed( |
| items: List<T>, |
| itemContent: @Composable LazyItemScope.(index: Int, item: T) -> Unit |
| ) { |
| intervals.add(items.size) { index -> |
| val item = items[index] |
| @Composable { itemContent(index, item) } |
| } |
| } |
| |
| @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) |
| } |
| } |