fillMaxWidth

Functions summary

Modifier
Modifier.fillMaxWidth(fraction: @FloatRange(from = 0.0, to = 1.0) Float)

Have the content fill (possibly only partially) the Constraints.maxWidth of the incoming measurement constraints, by setting the minimum width and the maximum width to be equal to the maximum width multiplied by fraction.
Cmn

Functions

Modifier.fillMaxWidth

Cmn 
fun Modifier.fillMaxWidth(fraction: @FloatRange(from = 0.0, to = 1.0) Float = 1.0f): Modifier

Have the content fill (possibly only partially) the Constraints.maxWidth of the incoming measurement constraints, by setting the minimum width and the maximum width to be equal to the maximum width multiplied by fraction. Note that, by default, the fraction is 1, so the modifier will make the content fill the whole available width. If the incoming maximum width is Constraints.Infinity this modifier will have no effect.

import androidx.compose.foundation.background
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.size
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.unit.dp

Box(Modifier.fillMaxWidth().background(Color.Red), contentAlignment = Alignment.Center) {
    Box(Modifier.size(100.dp).background(color = Color.Magenta))
}
 
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.requiredHeight
import androidx.compose.foundation.layout.requiredSize
import androidx.compose.ui.Alignment
import androidx.compose.ui.Modifier
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.unit.dp

Box(Modifier.requiredSize(100.dp).background(Color.Red), contentAlignment = Alignment.Center) {
    // The inner Box will be (50.dp x 30.dp).
    Box(
        Modifier.fillMaxWidth(fraction = 0.5f)
            .requiredHeight(30.dp)
            .background(color = Color.Magenta)
    )
}
Parameters
fraction: @FloatRange(from = 0.0, to = 1.0) Float = 1.0f

The fraction of the maximum width to use, between 0 and 1, inclusive.

Example usage: