| /* |
| * Copyright 2019 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.ui.core |
| |
| import androidx.ui.unit.IntPx |
| |
| /** |
| * The receiver scope of a layout's measure lambda. The return value of the |
| * measure lambda is [LayoutResult], which should be returned by [layout] |
| */ |
| abstract class MeasureScope : ModifierScope { |
| /** |
| * Interface holding the size and alignment lines of the measured layout, as well as the |
| * children positioning logic. |
| * [placeChildren] is the function used for positioning children. [Placeable.place] should |
| * be called on children inside [placeChildren]. |
| * The alignment lines can be used by the parent layouts to decide layout, and can be queried |
| * using the [Placeable.get] operator. Note that alignment lines will be inherited by parent |
| * layouts, such that indirect parents will be able to query them as well. |
| */ |
| interface LayoutResult { |
| val width: IntPx |
| val height: IntPx |
| val alignmentLines: Map<AlignmentLine, IntPx> |
| fun placeChildren(placementScope: Placeable.PlacementScope) |
| } |
| |
| /** |
| * Sets the size and alignment lines of the measured layout, as well as |
| * the positioning block that defines the children positioning logic. |
| * The [placementBlock] is a lambda used for positioning children. [Placeable.place] should |
| * be called on children inside placementBlock. |
| * The [alignmentLines] can be used by the parent layouts to decide layout, and can be queried |
| * using the [Placeable.get] operator. Note that alignment lines will be inherited by parent |
| * layouts, such that indirect parents will be able to query them as well. |
| * |
| * @param width the measured width of the layout |
| * @param height the measured height of the layout |
| * @param alignmentLines the alignment lines defined by the layout |
| * @param placementBlock block defining the children positioning of the current layout |
| */ |
| /*inline*/ fun layout( |
| width: IntPx, |
| height: IntPx, |
| alignmentLines: Map<AlignmentLine, IntPx> = emptyMap(), |
| /*crossinline*/ |
| placementBlock: Placeable.PlacementScope.() -> Unit |
| ) = object : LayoutResult { |
| override val width = width |
| override val height = height |
| override val alignmentLines = alignmentLines |
| override fun placeChildren(placementScope: Placeable.PlacementScope) = |
| placementScope.placementBlock() |
| } |
| |
| // Value comes from the ambient. Needed to provide an API that allows to restore the |
| // modified layout direction to ambient's state. |
| override var ambientLayoutDirection = LayoutDirection.Ltr |
| |
| // Stores the layout direction of the node that can be updated through the layout modifier. |
| override var layoutDirection = LayoutDirection.Ltr |
| } |
| |
| /** |
| * A function for performing layout measurement. |
| */ |
| typealias MeasureBlock = MeasureScope.(List<Measurable>, Constraints) -> MeasureScope.LayoutResult |