fillMaxSize

Functions summary

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

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

Functions

Modifier.fillMaxSize

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

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

import androidx.compose.foundation.background
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.fillMaxSize
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.fillMaxSize().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.fillMaxSize
import androidx.compose.foundation.layout.requiredSize
import androidx.compose.foundation.layout.requiredWidth
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 50.dp).
    Box(Modifier.requiredWidth(30.dp).fillMaxSize(0.5f).background(color = Color.Magenta))
}
Parameters
fraction: @FloatRange(from = 0.0, to = 1.0) Float = 1.0f

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

Example usage: