LazyGrid.kt
/*
* 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.layout.PaddingValues
import androidx.compose.foundation.layout.Row
import androidx.compose.foundation.layout.Spacer
import androidx.compose.runtime.Composable
import androidx.compose.ui.layout.Layout
import androidx.compose.ui.Modifier
import androidx.compose.ui.unit.Constraints
import androidx.compose.ui.unit.dp
/**
* The DSL implementation of a lazy grid layout. It composes only visible rows of the grid.
* This API is not stable, please consider using stable components like [LazyColumnFor] and [Row]
* to achieve the same result.
*
* @param columns a fixed number of columns of the grid
* @param modifier the modifier to apply to this layout
* @param contentPadding specify a padding around the whole content
* @param content the [LazyListScope] which describes the content
*/
@Composable
internal fun LazyGrid(
columns: Int,
modifier: Modifier = Modifier,
state: LazyListState = rememberLazyListState(),
contentPadding: PaddingValues = PaddingValues(0.dp),
content: LazyListScope.() -> Unit
) {
val scope = LazyListScopeImpl()
scope.apply(content)
val rows = (scope.totalSize + columns - 1) / columns
LazyList(
itemsCount = rows,
modifier = modifier,
state = state,
contentPadding = contentPadding,
isVertical = true
) { rowIndex ->
{
GridRow {
for (columnIndex in 0 until columns) {
val itemIndex = rowIndex * columns + columnIndex
if (itemIndex < scope.totalSize) {
scope.contentFor(itemIndex, this).invoke()
} else {
Spacer(Modifier)
}
}
}
}
}
}
@Composable
private fun GridRow(
children: @Composable () -> Unit
) {
// TODO: Implement customisable column widths.
Layout(
children = children
) { measurables, constraints ->
// TODO: Avoid int rounding to fill all the width pixels.
val itemConstraint = Constraints.fixedWidth(constraints.maxWidth / measurables.size)
var maxItemHeight = 0
val placeables = measurables.map { measurable ->
measurable.measure(itemConstraint)
.also {
if (it.height > maxItemHeight) {
maxItemHeight = it.height
}
}
}
layout(constraints.maxWidth, maxItemHeight) {
var currentXPosition = 0
placeables.forEach { placeable ->
placeable.placeRelative(x = currentXPosition, y = 0)
currentXPosition += placeable.width
}
}
}
}