Scrolling Composites in SWT

scrolling-swt.rb

#! /usr/bin/env jruby

require 'swt'

# swt gem doesn't appear to import the ScrolledComposite we need
# Looking at docs it's plenty old enough to be in any Java version we support
module Swt
  include_package 'org.eclipse.swt.custom'

  module Custom
    import org.eclipse.swt.custom.ScrolledComposite
  end
end

class SwtExample
  def initialize
    display = Swt::Widgets::Display.new
    red = display.get_system_color ::Swt::SWT::COLOR_RED
    blue = display.get_system_color ::Swt::SWT::COLOR_BLUE

    @shell = Swt::Widgets::Shell.new
    @shell.text = "Example"

    # This puts us in absolute mode, so we need to set everyone's position
    # explicitly. Fortunately, that's what we actually want since as a library
    # with our own positioning rules, we *know* where everything ought to be.
    @shell.layout = nil
    @shell.set_size 200, 200

    # Call our method to set up the necessary scrollable composites
    scroll_composite1, inner_composite1 = create_composite "yo", red

    # As mentioned before, we're responsible for all positioning
    # Outer composite is positioned relative to the main app
    scroll_composite1.set_bounds 0, 0, 100, 200

    # Inner composite positioning relative to the scrolling container
    inner_composite1.set_bounds 0, 0, 100, 1000

    # Repeat same steps to make a second scrollable composite
    scroll_composite2, inner_composite2 = create_composite "dawg", blue
    scroll_composite2.set_bounds 100, 0, 100, 200
    inner_composite2.set_bounds 0, 0, 100, 1000

    @shell.open
  end

  def create_composite(string, color)
    # Outer composite that actually responds to scrolling
    scroll = Swt::Custom::ScrolledComposite.new @shell, ::Swt::SWT::V_SCROLL

    # Inner composite "content" that we'll append our controls into
    composite = Swt::Widgets::Composite.new scroll, ::Swt::SWT::NONE

    # Setting layout to nil puts us in charge of absolute positioning
    # If we *don't* set the bounds with this layout, we get blank screens. Fun.
    composite.layout = nil

    # Set inner composite as the content of the scrolling composite
    scroll.content = composite

    # Adding controls and colors just for display purposes here... reaminder of
    # this method isn't critical to the core functionality.
    composite.background = color

    text = Swt::Widgets::Text.new composite, ::Swt::SWT::MULTI | ::Swt::SWT::WRAP
    text.text = "#{string} " * 10
    text.set_bounds 10, 60, 80, 50

    button = Swt::Widgets::Button.new composite, ::Swt::SWT::NONE
    button.text = string
    button.set_bounds 10, 10, 80, 50
    button.add_listener ::Swt::SWT::Selection do
      # Inch our scrolling along. This will be accessible probably via scroll_top or
      # some related thing...
      point = scroll.get_origin
      point.y += 10
      scroll.set_origin point
    end

    # Return so outer method here can tweak the positioning on both pieces
    [scroll, composite]
  end

  # This is the main gui event loop
  def start
    display = Swt::Widgets::Display.get_current

    # until the window (the Shell) has been closed
    while !@shell.isDisposed

      # check for and dispatch new gui events
      display.sleep unless display.read_and_dispatch
    end

    display.dispose
  end
end

Swt::Widgets::Display.set_app_name "Example"

app = SwtExample.new
app.start