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Class jcsp.awt.ActiveChoice

java.lang.Object
   |
   +----java.awt.Component
           |
           +----java.awt.Choice
                   |
                   +----jcsp.awt.ActiveChoice

public class ActiveChoice
extends Choice
implements CSProcess

Process Diagram

External View

             ______________
  configure |              | event
 ----->-----| ActiveChoice |--->---
            |______________|

Internal View

             ________________________________________
            |  ____________      __________________  |
  configure | |            |    |                  | | event
 ----->-------|  Configure |    | ItemEventHandler |----->---
            | |____________|    |__________________| |
            |                                        |
            |                           ActiveChoice |
            |________________________________________|

Description

An ActiveChoice is a sub class of Choice which uses Channels for event notification and configuration.

If the event Channel is not a null reference an new ItemEventHandler is created with the Channel and registered as ItemListener with the ActiveChoice and has its itemStateChanged() method invoked when ItemEvents are generated. Any events generated when the ItemEventHandler is blocked writing to the event Channel are ignored so that the main Java Event Thread is not blocked. The output from the ItemEventHanlder is connected to the event Channel causing an Object to be sent down the Channel when the Choice is selected.

NOTE: As the component generates two Objects for each event the event Channel must be a One2OneChannel.

It is also possible to register Channels to be used to notify the occurrence of other types of Event that the Choice generates. This can be done by calling one of the addXXXXEventChannel() methods.

To configure the Choice messages can be sent down the configure channel. If the configure Channel is not a null reference a new Configure is created. The configure process sits in an infinite loop which reads from the configure Channel and configures the component based on the Object received (see table below for details).

Channel Protocols

Input Channels
configure	String	Sets the selected item in this Choice menu to be the item whose name is equal to the specified string. If more than one item matches (is equal to) the specified string, the one with the smallest index is selected.
	Integer	Sets the selected item in this Choice menu to be the item at the specified position.
	Boolean	If the Boolean Object refers to the Boolean.TRUE instance the button is made active If the Boolean Object refers to the Boolean.FALSE instance the button is made inactive If the Boolean Object refers to any other Boolean instance the message is discarded
Output Channels
event	Boolean followed by Object	This component sends two Objects for each event. The first is a Boolean which will be true if the event was for selection false if it was for deselection. The second is an Object representing the item that changed.

Example

 import java.awt.*;
 import jcsp.lang.*;
 import jcsp.awt.*;
 public class ChoiceExample extends Frame {
   public ChoiceExample() {
     super("Choice Example");
     final Channel close = new One2OneChannel();
     ActiveChoice c = new ActiveChoice(null, close);
     c.add("Ignore Me");
     c.add("Close Window");
     add(c);
     setVisible(true);
     new Parallel(new CSProcess[] {
       c,
       new CSProcess() {
         public void run() {
           close.read();
           Integer i = (Integer)close.read();
           if (i.intValue() == 1) {
             setVisible(false);
             System.exit(0);
           }
         }
       }
     }).run();
   }
   public static void main(String argv[]) {
     new ChoiceExample();
   }
 }

Author:: P.D.Austin
See Also:: ItemEventHandler

ActiveChoice(): Constructs a Choice with no configuration Channel and no event Channel.
ActiveChoice(ChannelInput, ChannelOutput): Constructs a Choice with the configuration Channel configure and the event Channel event.

addComponentEventChannel(ChannelOutput): Add a new Channel to the Component which will be used to notify that a ComponentEvent has occurred on the component.
addFocusEventChannel(ChannelOutput): Add a new Channel to the Component which will be used to notify that a FocusEvent has occurred on the component.
addKeyEventChannel(ChannelOutput): Add a new Channel to the Component which will be used to notify that a KeyEvent has occurred on the component.
addMouseEventChannel(ChannelOutput): Add a new Channel to the Component which will be used to notify that a MouseEvent has occurred on the component.
addMouseMotionEventChannel(ChannelOutput): Add a new Channel to the Component which will be used to notify that a MouseMotionEvent has occurred on the component.
run(): The main body of this process.

ActiveChoice

 public ActiveChoice()

Constructs a Choice with no configuration Channel and no event Channel.

ActiveChoice

 public ActiveChoice(ChannelInput configure,
                     ChannelOutput event)

Constructs a Choice with the configuration Channel configure and the event Channel event.

Parameters:: configure - The Channel configuration events should be sent down. Can be null if no configuration is required.; event - The Channel events will be notified down when the button is pressed. Can be null if events are going to be ignored.

addComponentEventChannel

 public void addComponentEventChannel(ChannelOutput componentEvent)

Add a new Channel to the Component which will be used to notify that a ComponentEvent has occurred on the component. This should be used instead of registering a ComponentListener with the component. It is possible to add more than one Channel by calling this method multiple times If the reference passed is null no action will be taken. Otherwise a new ComponentEventHanlder will be generated for the Channel so that each Channel operates independently of the others.