| Andrey Kulikov | 2ca0701 | 2020-07-13 16:14:03 +0100 | [diff] [blame] | 1 | /* |
| 2 | * Copyright 2020 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | package androidx.ui.core |
| 18 | |
| 19 | import androidx.compose.Applier |
| 20 | import androidx.compose.Composable |
| 21 | import androidx.compose.ComposeCompilerApi |
| 22 | import androidx.compose.Composition |
| 23 | import androidx.compose.CompositionLifecycleObserver |
| 24 | import androidx.compose.CompositionReference |
| 25 | import androidx.compose.ExperimentalComposeApi |
| 26 | import androidx.compose.Recomposer |
| 27 | import androidx.compose.compositionReference |
| 28 | import androidx.compose.currentComposer |
| 29 | import androidx.compose.emit |
| 30 | import androidx.compose.remember |
| 31 | import androidx.ui.core.LayoutNode.LayoutState.LayingOut |
| 32 | import androidx.ui.core.LayoutNode.LayoutState.Measuring |
| 33 | import androidx.ui.core.MeasureScope.MeasureResult |
| 34 | import androidx.ui.util.fastForEach |
| 35 | |
| 36 | @RequiresOptIn( |
| 37 | "This is an experimental API for being able to perform subcomposition during the " + |
| 38 | "measuring. API is likely to change before becoming stable." |
| 39 | ) |
| 40 | annotation class ExperimentalSubcomposeLayoutApi |
| 41 | |
| 42 | /** |
| 43 | * Analogue of [Layout] which allows to subcompose the actual content during the measuring stage |
| 44 | * for example to use the values calculated during the measurement as params for the composition |
| 45 | * of the children. |
| 46 | * |
| 47 | * Possible use cases: |
| 48 | * * You need to know the constraints passed by the parent during the composition and can't solve |
| 49 | * your use case with just custom [Layout] or [LayoutModifier]. See [WithConstraints]. |
| 50 | * * You want to use the size of one child during the composition of the second child. Example is |
| 51 | * using the sizes of the tabs in TabRow as a input in tabs indicator composable |
| 52 | * * You want to compose your items lazily based on the available size. For example you have a |
| 53 | * list of 100 items and instead of composing all of them you only compose the ones which are |
| 54 | * currently visible(say 5 of them) and compose next items when the component is scrolled. |
| 55 | * |
| 56 | * @sample androidx.ui.core.samples.SubcomposeLayoutSample |
| 57 | * |
| 58 | * @param modifier [Modifier] to apply for the layout. |
| 59 | * @param measureBlock Measure block which provides ability to subcompose during the measuring. |
| 60 | */ |
| 61 | @Composable |
| 62 | @OptIn(ExperimentalLayoutNodeApi::class, ExperimentalComposeApi::class, ComposeCompilerApi::class) |
| 63 | @ExperimentalSubcomposeLayoutApi |
| 64 | fun <T> SubcomposeLayout( |
| 65 | modifier: Modifier = Modifier, |
| 66 | measureBlock: SubcomposeMeasureScope<T>.(Constraints) -> MeasureResult |
| 67 | ) { |
| 68 | val state = remember { SubcomposeLayoutState<T>() } |
| 69 | // TODO(lelandr): refactor these APIs so that recomposer isn't necessary |
| 70 | state.recomposer = currentComposer.recomposer |
| 71 | state.compositionRef = compositionReference() |
| 72 | |
| 73 | val materialized = currentComposer.materialize(modifier) |
| 74 | emit<LayoutNode, Applier<Any>>( |
| 75 | ctor = LayoutEmitHelper.constructor, |
| 76 | update = { |
| 77 | set(Unit, state.setRoot) |
| 78 | set(materialized, LayoutEmitHelper.setModifier) |
| 79 | set(measureBlock, state.setMeasureBlock) |
| 80 | } |
| 81 | ) |
| 82 | |
| 83 | state.subcomposeIfRemeasureNotScheduled() |
| 84 | } |
| 85 | |
| 86 | /** |
| 87 | * The receiver scope of a [SubcomposeLayout]'s measure lambda which adds ability to dynamically |
| 88 | * subcompose a content during the measuring on top of the features provided by [MeasureScope]. |
| 89 | */ |
| 90 | @ExperimentalSubcomposeLayoutApi |
| 91 | abstract class SubcomposeMeasureScope<T> : MeasureScope() { |
| 92 | /** |
| 93 | * Performs subcomposition of the provided [content] with given [slotId]. |
| 94 | * |
| 95 | * @param slotId unique id which represents the slot we are composing into. If you have fixed |
| 96 | * amount or slots you can use enums as slot ids, or if you have a list of items maybe an |
| 97 | * index in the list or some other unique key can work. To be able to correctly match the |
| 98 | * content between remeasures you should provide the object which is equals to the one you |
| 99 | * used during the previous measuring. |
| 100 | * @param content the composable content which defines the slot. It could emit multiple |
| 101 | * layouts, in this case the returned list of [Measurable]s will have multiple elements. |
| 102 | */ |
| 103 | abstract fun subcompose(slotId: T, content: @Composable () -> Unit): List<Measurable> |
| 104 | } |
| 105 | |
| 106 | @OptIn(ExperimentalLayoutNodeApi::class, ExperimentalSubcomposeLayoutApi::class) |
| 107 | private class SubcomposeLayoutState<T> : SubcomposeMeasureScope<T>(), |
| 108 | CompositionLifecycleObserver { |
| 109 | // Values set during the composition |
| 110 | var recomposer: Recomposer? = null |
| 111 | var compositionRef: CompositionReference? = null |
| 112 | |
| 113 | // MeasureScope delegation |
| 114 | override var layoutDirection: LayoutDirection = LayoutDirection.Rtl |
| 115 | override var density: Float = 0f |
| 116 | override var fontScale: Float = 0f |
| 117 | |
| 118 | // Pre-allocated lambdas to update LayoutNode |
| 119 | val setRoot: LayoutNode.(Unit) -> Unit = { root = this } |
| 120 | val setMeasureBlock: |
| 121 | LayoutNode.(SubcomposeMeasureScope<T>.(Constraints) -> MeasureResult) -> Unit = |
| 122 | { measureBlocks = createMeasureBlocks(it) } |
| 123 | |
| 124 | // inner state |
| 125 | private var root: LayoutNode? = null |
| 126 | private var currentIndex = 0 |
| 127 | private val nodeToNodeState = mutableMapOf<LayoutNode, NodeState<T>>() |
| 128 | private val slodIdToNode = mutableMapOf<T, LayoutNode>() |
| 129 | |
| 130 | override fun subcompose(slotId: T, content: @Composable () -> Unit): List<Measurable> { |
| 131 | val root = root!! |
| 132 | val layoutState = root.layoutState |
| 133 | check(layoutState == Measuring || layoutState == LayingOut) { |
| 134 | "subcompose can only be used inside the measure or layout blocks" |
| 135 | } |
| 136 | |
| 137 | val node = slodIdToNode.getOrPut(slotId) { |
| 138 | LayoutNode(isVirtual = true).also { |
| 139 | root.insertAt(currentIndex, it) |
| 140 | } |
| 141 | } |
| 142 | |
| 143 | val itemIndex = root.foldedChildren.indexOf(node) |
| 144 | if (itemIndex < currentIndex) { |
| 145 | throw IllegalArgumentException( |
| 146 | "$slotId was already used with subcompose during this measuring pass" |
| 147 | ) |
| 148 | } |
| 149 | if (currentIndex != itemIndex) { |
| 150 | root.move(itemIndex, currentIndex, 1) |
| 151 | } |
| 152 | currentIndex++ |
| 153 | |
| 154 | val nodeState = nodeToNodeState.getOrPut(node) { |
| 155 | NodeState(slotId, content) |
| 156 | } |
| 157 | nodeState.content = content |
| 158 | subcompose(node, nodeState) |
| 159 | return node.children |
| 160 | } |
| 161 | |
| 162 | fun subcomposeIfRemeasureNotScheduled() { |
| 163 | val root = root!! |
| 164 | if (root.layoutState != LayoutNode.LayoutState.NeedsRemeasure) { |
| 165 | root.foldedChildren.fastForEach { |
| 166 | subcompose(it, nodeToNodeState.getValue(it)) |
| 167 | } |
| 168 | } |
| 169 | } |
| 170 | |
| 171 | private fun subcompose(node: LayoutNode, nodeState: NodeState<T>) { |
| 172 | node.ignoreModelReads { |
| 173 | val content = nodeState.content |
| 174 | nodeState.composition = subcomposeInto(node, recomposer!!, compositionRef!!) { |
| 175 | content() |
| 176 | } |
| 177 | } |
| 178 | } |
| 179 | |
| 180 | private fun disposeAfterIndex(currentIndex: Int) { |
| 181 | val root = root!! |
| 182 | for (i in currentIndex until root.foldedChildren.size) { |
| 183 | val node = root.foldedChildren[i] |
| 184 | val nodeState = nodeToNodeState.remove(node)!! |
| 185 | nodeState.composition!!.dispose() |
| 186 | slodIdToNode.remove(nodeState.slotId) |
| 187 | } |
| 188 | root.removeAt(currentIndex, root.foldedChildren.size - currentIndex) |
| 189 | } |
| 190 | |
| 191 | private fun createMeasureBlocks( |
| 192 | block: SubcomposeMeasureScope<T>.(Constraints) -> MeasureResult |
| 193 | ): LayoutNode.MeasureBlocks = object : LayoutNode.NoIntrinsicsMeasureBlocks( |
| 194 | error = "Intrinsic measurements are not currently supported by SubcomposeLayout" |
| 195 | ) { |
| 196 | override fun measure( |
| 197 | measureScope: MeasureScope, |
| 198 | measurables: List<Measurable>, |
| 199 | constraints: Constraints, |
| 200 | layoutDirection: LayoutDirection |
| 201 | ): MeasureResult { |
| 202 | this@SubcomposeLayoutState.layoutDirection = measureScope.layoutDirection |
| 203 | this@SubcomposeLayoutState.density = measureScope.density |
| 204 | this@SubcomposeLayoutState.fontScale = measureScope.fontScale |
| 205 | currentIndex = 0 |
| 206 | val result = block(constraints) |
| 207 | val indexAfterMeasure = currentIndex |
| 208 | return object : MeasureResult { |
| 209 | override val width: Int |
| 210 | get() = result.width |
| 211 | override val height: Int |
| 212 | get() = result.height |
| 213 | override val alignmentLines: Map<AlignmentLine, Int> |
| 214 | get() = result.alignmentLines |
| 215 | |
| 216 | override fun placeChildren(layoutDirection: LayoutDirection) { |
| 217 | currentIndex = indexAfterMeasure |
| 218 | result.placeChildren(layoutDirection) |
| 219 | disposeAfterIndex(currentIndex) |
| 220 | } |
| 221 | } |
| 222 | } |
| 223 | } |
| 224 | |
| 225 | override fun onEnter() { |
| 226 | // do nothing |
| 227 | } |
| 228 | |
| 229 | override fun onLeave() { |
| 230 | nodeToNodeState.values.forEach { |
| 231 | it.composition!!.dispose() |
| 232 | } |
| 233 | nodeToNodeState.clear() |
| 234 | slodIdToNode.clear() |
| 235 | } |
| 236 | |
| 237 | private class NodeState<T>( |
| 238 | val slotId: T, |
| 239 | var content: @Composable () -> Unit, |
| 240 | var composition: Composition? = null |
| 241 | ) |
| 242 | } |