Autosize Text

Author: Brandon McAnsh

A Compose implementation of the autosize functionality in TextView since it's not yet available out-of-the-box. The AutosizeText function takes width/height constraints and chooses the maximum fontSize that can render the text.

import androidx.compose.material.LocalTextStyle
import androidx.compose.material.Text
import androidx.compose.runtime.*
import androidx.compose.ui.Modifier
import androidx.compose.ui.draw.drawWithContent
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.text.AnnotatedString
import androidx.compose.ui.text.TextStyle
import androidx.compose.ui.text.font.FontFamily
import androidx.compose.ui.text.font.FontStyle
import androidx.compose.ui.text.font.FontWeight
import androidx.compose.ui.text.style.TextAlign
import androidx.compose.ui.text.style.TextDecoration
import androidx.compose.ui.text.style.TextOverflow
import androidx.compose.ui.unit.TextUnit

sealed class AutoSizeConstraint(open val min: TextUnit = TextUnit.Unspecified) {
    data class Width(override val min: TextUnit = TextUnit.Unspecified): AutoSizeConstraint(min)
    data class Height(override val min: TextUnit = TextUnit.Unspecified): AutoSizeConstraint(min)
}

@Composable
fun AutoSizeText(
    text: AnnotatedString,
    modifier: Modifier = Modifier,
    color: Color = Color.Unspecified,
    fontSize: TextUnit = TextUnit.Unspecified,
    fontStyle: FontStyle? = null,
    fontWeight: FontWeight? = null,
    fontFamily: FontFamily? = null,
    letterSpacing: TextUnit = TextUnit.Unspecified,
    textDecoration: TextDecoration? = null,
    textAlign: TextAlign? = null,
    lineHeight: TextUnit = TextUnit.Unspecified,
    overflow: TextOverflow = TextOverflow.Clip,
    softWrap: Boolean = true,
    maxLines: Int = Int.MAX_VALUE,
    style: TextStyle = LocalTextStyle.current,
    constraint: AutoSizeConstraint = AutoSizeConstraint.Width(),
) {
    var textStyle by remember { mutableStateOf(style) }
    var readyToDraw by remember { mutableStateOf(false) }

    Text(
        modifier = modifier.drawWithContent {
            if (readyToDraw) drawContent()
        },
        text = text,
        color = color,
        fontSize = fontSize,
        fontStyle = fontStyle,
        fontWeight = fontWeight,
        fontFamily = fontFamily,
        letterSpacing = letterSpacing,
        textDecoration = textDecoration,
        textAlign = textAlign,
        lineHeight = lineHeight,
        overflow = overflow,
        softWrap = softWrap,
        maxLines = maxLines,
        style = style,
        onTextLayout = { result ->
            fun constrain() {
                val reducedSize = textStyle.fontSize * 0.9f
                if (constraint.min != TextUnit.Unspecified && reducedSize <= constraint.min) {
                    textStyle = textStyle.copy(fontSize = constraint.min)
                    readyToDraw = true
                } else {
                    textStyle = textStyle.copy(fontSize = textStyle.fontSize * 0.9f)
                }
            }

            when (constraint) {
                is AutoSizeConstraint.Height -> {
                    if (result.didOverflowHeight) {
                        constrain()
                    } else {
                        readyToDraw = true
                    }
                }
                is AutoSizeConstraint.Width -> {
                    if (result.didOverflowWidth) {
                        constrain()
                    } else {
                        readyToDraw = true
                    }
                }
            }
        }
    )
}

@Composable
fun AutoSizeText(
    text: String,
    modifier: Modifier = Modifier,
    color: Color = Color.Unspecified,
    fontSize: TextUnit = TextUnit.Unspecified,
    fontStyle: FontStyle? = null,
    fontWeight: FontWeight? = null,
    fontFamily: FontFamily? = null,
    letterSpacing: TextUnit = TextUnit.Unspecified,
    textDecoration: TextDecoration? = null,
    textAlign: TextAlign? = null,
    lineHeight: TextUnit = TextUnit.Unspecified,
    overflow: TextOverflow = TextOverflow.Clip,
    softWrap: Boolean = true,
    maxLines: Int = Int.MAX_VALUE,
    style: TextStyle = LocalTextStyle.current,
    constraint: AutoSizeConstraint = AutoSizeConstraint.Width(),
) {
    AutoSizeText(
        modifier = modifier,
        text = AnnotatedString(text),
        color = color,
        fontSize = fontSize,
        fontStyle = fontStyle,
        fontWeight = fontWeight,
        fontFamily = fontFamily,
        letterSpacing = letterSpacing,
        textDecoration = textDecoration,
        textAlign = textAlign,
        lineHeight = lineHeight,
        overflow = overflow,
        softWrap = softWrap,
        maxLines = maxLines,
        style = style,
        constraint = constraint
    )
}