HeightInLinesModifier.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.text
import androidx.compose.foundation.layout.heightIn
import androidx.compose.runtime.getValue
import androidx.compose.runtime.remember
import androidx.compose.ui.Modifier
import androidx.compose.ui.composed
import androidx.compose.ui.platform.LocalDensity
import androidx.compose.ui.platform.LocalFontFamilyResolver
import androidx.compose.ui.platform.LocalLayoutDirection
import androidx.compose.ui.platform.debugInspectorInfo
import androidx.compose.ui.text.TextStyle
import androidx.compose.ui.text.font.FontStyle
import androidx.compose.ui.text.font.FontSynthesis
import androidx.compose.ui.text.font.FontWeight
import androidx.compose.ui.text.resolveDefaults
import androidx.compose.ui.unit.Dp
/**
* The default minimum height in terms of minimum number of visible lines.
*/
internal const val DefaultMinLines: Int = 1
/**
* Constraint the height of the text field so that it vertically occupies at least [minLines]
* number of lines and at most [maxLines] number of lines.
*/
internal fun Modifier.heightInLines(
textStyle: TextStyle,
minLines: Int = DefaultMinLines,
maxLines: Int = Int.MAX_VALUE
) = composed(
inspectorInfo = debugInspectorInfo {
name = "heightInLines"
properties["minLines"] = minLines
properties["maxLines"] = maxLines
properties["textStyle"] = textStyle
}
) {
require(minLines > 0) {
"minLines must be greater than 0"
}
require(maxLines > 0) {
"maxLines must be greater than 0"
}
require(minLines <= maxLines) {
"minLines $minLines must be lower than or equal to maxLines $maxLines"
}
if (minLines == DefaultMinLines && maxLines == Int.MAX_VALUE) return@composed Modifier
val density = LocalDensity.current
val fontFamilyResolver = LocalFontFamilyResolver.current
val layoutDirection = LocalLayoutDirection.current
// Difference between the height of two lines paragraph and one line paragraph gives us
// an approximation of height of one line
val resolvedStyle = remember(textStyle, layoutDirection) {
resolveDefaults(textStyle, layoutDirection)
}
val typeface by remember(fontFamilyResolver, resolvedStyle) {
fontFamilyResolver.resolve(
resolvedStyle.fontFamily,
resolvedStyle.fontWeight ?: FontWeight.Normal,
resolvedStyle.fontStyle ?: FontStyle.Normal,
resolvedStyle.fontSynthesis ?: FontSynthesis.All
)
}
val firstLineHeight = remember(
density,
fontFamilyResolver,
textStyle,
layoutDirection,
typeface
) {
computeSizeForDefaultText(
style = resolvedStyle,
density = density,
fontFamilyResolver = fontFamilyResolver,
text = EmptyTextReplacement,
maxLines = 1
).height
}
val firstTwoLinesHeight = remember(
density,
fontFamilyResolver,
textStyle,
layoutDirection,
typeface
) {
val twoLines = EmptyTextReplacement + "\n" + EmptyTextReplacement
computeSizeForDefaultText(
style = resolvedStyle,
density = density,
fontFamilyResolver = fontFamilyResolver,
text = twoLines,
maxLines = 2
).height
}
val lineHeight = firstTwoLinesHeight - firstLineHeight
val precomputedMinLinesHeight =
if (minLines == DefaultMinLines) null else firstLineHeight + lineHeight * (minLines - 1)
val precomputedMaxLinesHeight =
if (maxLines == Int.MAX_VALUE) null else firstLineHeight + lineHeight * (maxLines - 1)
with(density) {
Modifier.heightIn(
min = precomputedMinLinesHeight?.toDp() ?: Dp.Unspecified,
max = precomputedMaxLinesHeight?.toDp() ?: Dp.Unspecified
)
}
}