In scala.swing, how do I remove a component from a Container?

Question

In scala.swing, I can add a component to a container like so:

new Frame {
  contents += label
}

but sometimes I'd like to clear the contents of a container and replace them with new components. Based on the docs, I should be able to do:

frame.contents.remove(0)

or

frame.contents.clear

but neither of those compile ("clear/remove is not a member of Seq[scala.swing.Component]").

How can I resolve this? Also, it seems that I can't call frame.contents += blah after intialization. If this is so, how do I add a new component to a Container?

Answer 1

If you're talking about Frame specifically, you can only add one item, so use the method

def contents_= (c: Component) : Unit

and you should be good. Try this out in the REPL (one line at a time so you can see what's going on):

import scala.swing._
val f = new Frame { contents = new Label("Hi") }
f.visible = true
f.contents = new Label("Hey there")

If you're using something that is intended to have multiple items like a BoxPanel, contents is a Buffer so you can add to it and remove from it:

val bp = new BoxPanel(Orientation.Vertical)
val (label1,label2) = (new Label("Hi"), new Label("there"))
bp.contents += label1
bp.contents += label2
f.contents = bp    // Now you see "Hi" "there" stacked
bp.contents -= label1
f.pack             // "Hi" disappears--need pack not repaint to fix layout
bp.contents += label1
f.pack             // "Hi" is back, but at the end

If you have something else like a Component that you're extending, it is your job to override contents with a buffer or have some other way of modifying it (or inherit from SequentialContainer as J-16 said).

Answer 2

contents in Container was a Seq[]; you need a SequentialContainer for that remove method.