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Class jcsp.awt.event.FocusEventHandler

java.lang.Object
   |
   +----jcsp.awt.event.FocusEventHandler

public class FocusEventHandler

extends Object

implements CSProcess, FocusListener

Process Diagram

   ___________________
  |                   | event
  | FocusEventHandler |--->---
  |___________________|
 

Description

The FocusEventHandler class implements the FocusListener interface and can be used for any Component which allows the addition of a FocusListener. When the Component is created a new instance of the FocusEventHandler should be created and added as a FocusListener to the Component. The process must be set running (either asynchronously using ProcessNetwork or as part of a Parallel construct).

The main body of this process waits to be notified by a component invoking the focusGained() or focusLost() methods. The process then wakes up and sends the FocusEvent object down the event Channel. Any further calls to the methods while the process is writing will be discarded so as not to block the main Java event Thread. When another process reads from the Channel this process loops round and waits to be notified again.

Channel Protocols

Example

Extending an Existing Component

 import java.awt.*;
 import jcsp.lang.*;
 import jcsp.awt.event.*;
 public class ChannelComponent extends Component implements CSProcess {
   FocusEventHanlder handler;
   public ChannelComponent() {
   }
   public void addFocusEventChannel(ChannelOutput event) {
     if (event !=null) {
       handler = new FocusEventHanlder(event);
       addFocusListener(handler);
     }
   }
   public void run() {
     if (handler != null) {
       handler.run();
     }
   }
 }
 

Listening to a Component

 import java.awt.*;
 import jcsp.awt.event.*;
 import jcsp.lang.*;
        :
        :
   {
     final Channel event = new One2OneChannel();
     Component c = new Button("Active");
     add(c);
     FocusEventHanlder handler = new FocusEventHanlder(event);
     c.addFocusListener(handler);
     new Parallel(new CSProcess[] {
       c,
       handler,
       new CSProcess() {
         public void run() {
           while (true) {
             Object o = event.read();
             System.out.println("FocusEvent '" + o);
           }
         }
       }
     }).run();
   }
 }
 

Author:

P.D.Austin

FocusEventHandler(ChannelOutput)

constructs a new FocusEventHandler with the specified output Channel.

focusGained(FocusEvent)

Invoked when the Component the event handler is listening to Gains the input Focus.

focusLost(FocusEvent)

Invoked when the Component the event handler is listening to Gains the input Focus.

run()

The main body of the process.

 public FocusEventHandler(ChannelOutput event)

constructs a new FocusEventHandler with the specified output Channel.

Parameters:

event - The Channel to send the event notification down

 public void focusGained(FocusEvent e)

Invoked when the Component the event handler is listening to Gains the input Focus. Notifies the event process that a FocusEvent has occurred by sending the FocusEvent Object. Some notifications will be lost so there are no guarantees that all events generated will be processed.

Parameters:

e - The parameters associated with this event

 public void focusLost(FocusEvent e)

Invoked when the Component the event handler is listening to Gains the input Focus. Notifies the event process that a FocusEvent has occurred by sending the FocusEvent Object. Some notifications will be lost so there are no guarantees that all events generated will be processed.

Parameters:

e - The parameters associated with this event

 public void run()

The main body of the process. Executes the functionality described above.

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