var text by rememberSaveable { mutableStateOf("") }

var isError by rememberSaveable { mutableStateOf(false) }

​

fun validate(text: String) {

    isError = /* .... */

}

​

Column {

    TextField(

        value = text,

        onValueChange = {

            text = it

            isError = false

        },

        trailingIcon = {

            if (isError)

            Icon(Icons.Filled.Error,"error", tint = MaterialTheme.colors.error)

        },

        singleLine = true,

        isError = isError,

        keyboardActions = KeyboardActions { validate(text) },

    )

    if (isError) {

        Text(

            text = "Error message",

            color = MaterialTheme.colors.error,

            style = MaterialTheme.typography.caption,

            modifier = Modifier.padding(start = 16.dp)

        )

    }

}