[java-gnome-hackers] Event Handling proposal

[Mark H. <mh...@ti...>]

Hi,
sorry for not suggesting this earlier - I was still learning how
Java-gnome worked back then.=20

I don't like the way event type checking is done:
if (event.getId() =3D=3D KeyEvent.PRESSED){
I think this would be better done something like:
if (event.isOfType(KeyEvent.Type.PRESSED) ){

This:
- ensures a type is used, not any arbitrary integer
- is immediately obvious to the developer
- is readable
- has better toString support (see below)


I have created the following sources to show how I propose it should be
done:

GtkEvent.java:
public class GtkEvent implements Serializable {
  protected GtkEventType type;
  protected Object source;

  public GtkEvent(Object source, GtkEventType type) {
    if (null =3D=3D source)
       throw new IllegalArgumentException("null source");
    this.source =3D source;
    this.type =3D type;
  }
  public Object getSource() {
    return source;
  }
  public int getType() {
    return type;
  }
  public String toString() {
   return getClass().getName() + "[source=3D" + source + ",id=3D" +
type.getName() + "]";
  }
}

GtkEventType.java:
public class GtkEventType{
  private int id;
  private String name;
  protected int getID(){
    return id;
  }
  protected String getName(){
    return name;
  }
  protected GtkEventType(int typeID, String typeName){
    id =3D typeID;
    name =3D typeName;
  }
}

Sample Event (ButtonEvent.java):
public class ButtonEvent extends GtkEvent {=09
  public static class Type extends GtkEventType{
    public static final ButtonEventType ACTIVATE =3D new ButtonEvent(1,
"ACTIVATE");
    public static final ButtonEventType CLICK =3D new ButtonEvent(2,
"CLICK");
    public static final ButtonEventType ENTER =3D new ButtonEvent(3,
"ENTER");
    public static final ButtonEventType LEAVE =3D new ButtonEvent(4,
"Leave");
    public static final ButtonEventType PRESS =3D new ButtonEvent(5,
"PRESS");
    public static final ButtonEventType RELEASE =3D new ButtonEvent(6,
"RELEASE");
   // the strings were defined separately using the old method.
  }
  public interface Listener{
    public void buttonEvent(ButtonEvent event );
  }
  public ButtonEvent(Object source, ButtonEvent.Type type) {
    super(source, type);
  }
  public boolean ofType(ButtonEvent.Type type){
    return ( id =3D=3D type.getID());
  }
}

I have not done extensive testing of this (as it would require changing
all the events and methods which use them), but I see no reason why it
shouldn't work - we are still dealing with exactly the same data.=20

I think this should be done for the simple reason that=20
event.isOfType( ButtonEvent.Type.CLICK )
is far more obvious to the developer (and it is readable)

The question of Type and Listener being done as inner classes is
debatable. Perhaps listener should be separate.

I am prepared to make the necessary changes to all the currently
implemented events and classes which use these.=20

Let me know your thoughts.
--=20

+----------------------------------------------+
| Mark Howard               cam.ac.uk   mh344@ |
| http://www.tildemh.com    tildemh.com    mh@ |
+----------------------------------------------+