RE: [java-gnome-hackers] Event Handling proposal

[Jeffrey M. <Jef...@Br...>]

I like this idea. 

-Jeff

> Hi,
> sorry for not suggesting this earlier - I was still learning how
> Java-gnome worked back then. 
> 
> I don't like the way event type checking is done:
> if (event.getId() == 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 == source)
>        throw new IllegalArgumentException("null source");
>     this.source = source;
>     this.type = type;
>   }
>   public Object getSource() {
>     return source;
>   }
>   public int getType() {
>     return type;
>   }
>   public String toString() {
>    return getClass().getName() + "[source=" + source + ",id=" +
> 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 = typeID;
>     name = typeName;
>   }
> }
> 
> Sample Event (ButtonEvent.java):
> public class ButtonEvent extends GtkEvent {	
>   public static class Type extends GtkEventType{
>     public static final ButtonEventType ACTIVATE = new ButtonEvent(1,
> "ACTIVATE");
>     public static final ButtonEventType CLICK = new ButtonEvent(2,
> "CLICK");
>     public static final ButtonEventType ENTER = new ButtonEvent(3,
> "ENTER");
>     public static final ButtonEventType LEAVE = new ButtonEvent(4,
> "Leave");
>     public static final ButtonEventType PRESS = new ButtonEvent(5,
> "PRESS");
>     public static final ButtonEventType RELEASE = 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 == 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. 
> 
> I think this should be done for the simple reason that 
> 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. 
> 
> Let me know your thoughts.
> -- 
> 
> +----------------------------------------------+
> | Mark Howard               cam.ac.uk   mh344@ |
> | http://www.tildemh.com    tildemh.com    mh@ |
> +----------------------------------------------+
>