properties of scala swing elements - swing

Question

In the following scala code I change foreground, horizontalAlignment and background to some values. However in the GUI these properties are not shown.
The horizontalAlignment remains centered.
The backgrould remains gray.
However the foreground (font color) changes according to the values.
How can I obtain the desired effects?
Thanks for any help!
import scala.swing._
object GuiTest extends SimpleSwingApplication {
def top = new MainFrame {
title = "Label Test"
val tempList = List("Celsius", "Fahrenheit", "Kelvin")
contents = bagPnl(tempList)
val fields = contents(0).peer.getComponents
val valuefields
= for (f <- 0 until fields.length / 2)
yield tempList(f) -> fields.apply(2 * f + 1).asInstanceOf[javax.swing.JLabel]
val tfm = valuefields.toMap[String, javax.swing.JLabel]
tfm.apply("Celsius").setText("35°C")
tfm.apply("Kelvin").setText("0 K")
}
def bagPnl(list: List[String]) = new GridBagPanel {
val gbc = new Constraints
gbc.insets = new Insets(3, 3, 3, 3)
var l = 0
for (title <- list) {
gbc.gridy = l
gbc.gridx = 0
/* title label */
add(new Label {
horizontalAlignment = Alignment.Left
foreground = java.awt.Color.RED
background = java.awt.Color.CYAN
text = title
}, gbc)
gbc.gridx = 1
/* value label */
val t = new Label {
horizontalAlignment = Alignment.Right
foreground = java.awt.Color.BLUE
background = java.awt.Color.YELLOW
name = title
}
t.background = java.awt.Color.GREEN
add(t, gbc)
l = l + 1
}
}
}
sorry I am not allowed to post images yet :-(

Answer 1

GridBagLayout is one hell of a layout manager. You'll be probably better of with GroupLayout, but there is no related panel type in Scala-Swing yet. (Here for an example).
The problem with the label positioning is that its alignment only makes sense when it is given more space than its preferred size. By default, the grid bag layout doesn't give it more space, and the centering is a result of its own alignment (not that of the label). The easiest here is to specify that the components can use up the horizontal space if available:
gbc.fill = GridBagPanel.Fill.Horizontal
The second questions concerns the background color of the label. Here is a related question. In short, by default the label is transparent and its background color ignored. You can switch to opaque painting:
new Label {
...
opaque = true
}