TextMeasurer gives different results than the actual Text in Jetpack Compose

Question

I'm trying to measure the number of lines of a Text without rendering it. I thought I could use a TextMeasurer, however the number of "measured" lines is different than the number of lines I get if I render the actual Text.

This is the code I'm using:

Box () {
    val textMeasurer = rememberTextMeasurer()
    val measuredLayoutResult = textMeasurer.measure(
        largeText)
    println("Measured lines: ${measuredLayoutResult.lineCount}, " +
            "Measured height: ${measuredLayoutResult.size.height}, " +
            "Measured width: ${measuredLayoutResult.size.width}")
    Text(
        largeText,
        onTextLayout = { textLayoutResult ->
            println("Actual lines: ${textLayoutResult.lineCount}, " +
                    "Actual height: ${textLayoutResult.size.height}, " +
                    "Actual width: ${textLayoutResult.size.width}")

        },
    )
}

I would expect the numbers to be the same, instead I'm getting the following: Measured lines: 25, Measured height: 1132, Measured width: 30154 Actual lines: 235, Actual height: 2088, Actual width: 1080

Any ideas what I am doing wrong?

Answer 1

When you don't assign constraints param to measure function of TextMeasurer it uses default Constraints with maxWidth and maxHeight with Constraints.Infinity.

@Stable
fun measure(
    text: String,
    style: TextStyle = TextStyle.Default,
    overflow: TextOverflow = TextOverflow.Clip,
    softWrap: Boolean = true,
    maxLines: Int = Int.MAX_VALUE,
    constraints: Constraints = Constraints(),
    layoutDirection: LayoutDirection = this.defaultLayoutDirection,
    density: Density = this.defaultDensity,
    fontFamilyResolver: FontFamily.Resolver = this.defaultFontFamilyResolver,
    skipCache: Boolean = false
)

Use a BoxWithConstraints and pass a Constraints from it to limit total width that text can be measured with

@Preview
@Composable
private fun Test() {

    val largeText =
        "some large tatasda sdasdasdsa dasdasd asda sdasd asdasd asdasdasdasdasdasdasdasdasd"
    BoxWithConstraints {

        val textMeasurer = rememberTextMeasurer()
        val measuredLayoutResult = textMeasurer.measure(
            constraints = constraints,
            text = largeText
        )
        println(
            "Measured lines: ${measuredLayoutResult.lineCount}, " +
                    "Measured height: ${measuredLayoutResult.size.height}, " +
                    "Measured width: ${measuredLayoutResult.size.width}"
        )
        Text(
            largeText,
            onTextLayout = { textLayoutResult ->
                println(
                    "Actual lines: ${textLayoutResult.lineCount}, " +
                            "Actual height: ${textLayoutResult.size.height}, " +
                            "Actual width: ${textLayoutResult.size.width}"
                )

            },
        )
    }
}