In addition to fundamental GUI component interaction, an application should
dynamically enable and disable GUI components, to give some guidance to the
user, and prohibit (inter)actions which are inappropriate in the current state
of the application.



Task

Similar to the task GUI component interaction, write a program
that presents a form with three components to the user:

   a numeric input field ("Value") 
   a button   ("increment")
   a button   ("decrement")


The field is initialized to zero.
The user may manually enter a new value into the field,
increment its value with the "increment" button,
or decrement the value with the "decrement" button.

The input field should be enabled only when its value is zero.
The "increment" button only as long as the field's value is less then 10:
When the value 10 is reached, the button should go into a disabled state.
Analogously, the "decrement" button should be enabled only as long as
the value is greater than zero.

Effectively, the user can now either increment up to 10, or down to zero.
Manually entering values outside that range is still legal,
but the buttons should reflect that and enable/disable accordingly.




import swing.{ BoxPanel, Button, GridPanel, Orientation, Swing, TextField }
import swing.event.{ ButtonClicked, Key, KeyPressed, KeyTyped }
 
object Enabling extends swing.SimpleSwingApplication {
  def top = new swing.MainFrame {
    title = "Rosetta Code >>> Task: GUI enabling/disabling of controls | Language: Scala"
 
    val numberField = new TextField {
      text = "0" // start at 0
      horizontalAlignment = swing.Alignment.Right
    }
 
    val (incButton, decButton) = (new Button("Increment"), // Two variables initialized
      new Button("Decrement") { enabled = false })
 
    // arrange buttons in a grid with 1 row, 2 columns
    val buttonPanel = new GridPanel(1, 2) { contents ++= List(incButton, decButton) }
 
    // arrange text field and button panel in a grid with 2 row, 1 column
    contents = new BoxPanel(Orientation.Vertical) { contents ++= List(numberField, buttonPanel) }
 
    val specialKeys = List(Key.BackSpace, Key.Delete)
 
    // listen for keys pressed in numberField and button clicks
    listenTo(numberField.keys, incButton, decButton)
    reactions += {
      case kt: KeyTyped =>
        if (kt.char.isDigit) // if the entered char is a digit ...
          Swing.onEDT(switching) // ensure GUI-updating
        else kt.consume // ... eat the event (i.e. stop it from being processed)
      case KeyPressed(_, kp, _, _) if (!specialKeys.contains(kp)) =>
        Swing.onEDT(switching) // ensure GUI-updating
      case ButtonClicked(`incButton`) =>
        numberField.text = (numberField.text.toLong + 1).toString
        switching
      case ButtonClicked(`decButton`) =>
        numberField.text = (numberField.text.toLong - 1).toString
        switching
    }
 
    def switching = {
      val n = (if (numberField.text.isEmpty()) "0" else numberField.text).toLong
      numberField.text = n.toString
      numberField.enabled = n == 0
      incButton.enabled = n < 10
      decButton.enabled = n > 0
    }
    centerOnScreen()
  } // def top(
}